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dissertation entitled

An Epidemiological Study of
Lameness in Michigan Horses

presented by

Whitney Allyson Ross, D.V.M.

has been accepted towards fulfillment
of the requirements for

Ph . D . degree in Epidemi0|ogy

Large Animal Clinical Sciences

W

Major professor

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AN EPIDEMIOLGICAL STUDY OF LAMENESS IN MICHIGAN HORSES
By

Whitney Allyson Ross, D.V.M.

A DISSERTATION

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Large Animal Clinical Sciences

1997

 

 

ABSTRACT

AN EPIDEMIOLGICAL STUDY OF LAMENESS IN MICHIGAN HORSES
By

Whitney Allyson Ross, D.V.M.

This dissertation summarizes the epidemiology of lameness in Michigan
horses, based on the Michigan Equine Monitoring System (MEMS) Phase—ll.
The MEMS Phase-ll, equine health-monitoring study, included a Stratified
random sample of equine operations in Michigan. The study was designed as
a prospective cohort epidemiological study in which data collection continued
for two 1—year periods. The primary objectives addressed focused on
describing the magnitude and severity of lameness in a population of horses
and on identifying risk factors that were associated with the occurrence of,
recovery from and duration of lameness. Multivariable statistical techniques,
including poisson regression, logistic regression with random effects, and Cox’s
proportional hazards regression were used to evaluate the association between
the occurrence of lameness and several risk factors at both the operation— and
individual-animal-levels.

Lameness was found to be an important cause of productivity loss,
especially with respect to the incidence and duration of cases and mortality
rate. Operations that had stalls with gravel or sand flooring and stalls bedded
with straw were 2 times more likely to have a reported lameness case,

compared to operations using other types of flooring or bedding. In contrast,

 

 

there was a 50% reduced risk of lameness on operations that had dirt or clay
flooring in stalls. It was also determined that increasing operation size was
associated with a reduced risk of lameness. This finding may be attributable
to the type of health management or environment available to horses or to the
types of horses that are generally kept in larger operations. It is noteworthy,
that operations perceiving veterinary and farrier services to be important had
relatively high rates of lameness, which may be attributable to improved
reporting or record—keeping systems on those operations.

Operations that had horses participating in exercise-related activities had
an almost 2-fold increase in the risk of having a horse become lame. On an
individual-animal-level, compared to all other horses, race horses and Show
horses were 70% and 40% more likely to experience lameness, respectively.
Furthermore, horses that were reported to have exercised during the study
period had at least a 2-fold increase in the risk of experiencing lameness.
These findings suggest that the risk of lameness is associated with the
occupation of the horse. Using survival analysis, it was also determined that
compared to mares, stallions and geldings had a 90% and 50% increased
chance of experiencing lameness, respectively. This may be attributable to the
types of activities required of males compared to mares. Active horses and
horses treated for lameness were almost twice as likely to recover from a case
of lameness; however, whether or not a horse was treated did not affect
lameness duration. This again may be a reflection of the type of health care

available to horses.

 

To my Mom and Dad, J. Sue and Sydney P. Ross, D.O., who instilled in
me a love for learning and for horses and who taught me the importance
of the pursuit of excellence, to my husband, Michael L. Mauer, D.V.M.,
who gives me the strength and support to meet life’s challenges, and to
my son, Michael R. Mauer, who makes it all worthwhile.

 

ACKNOWLEDGMENTS

I would, first, like to thank Dr. John Kaneene, my major advisor, for his
unending support of and enthusiasm for my program. I will always appreciate
his ability to see the "Big Picture," to consider things to be challenges, rather
than problems, and to always make time for his students ("I’ve been waiting").
I would also like to thank the other members of my committee: Dr. Joseph
Gardiner, Dr. John Caron, Dr. Ken Gallagher, and Dr. Ashley Robinson, whose
input and technical expertise were essential for completion of this project. I
appreciate their willingness to provide thoughtful comments and constructive
criticism and their E—mail accessibility.

Special thanks go to RoseAnn Miller, who "showed me the ropes."
Without her computer expertise, her experience and her creativity, this project
could not have run so smoothly. I would also like to thank my fellow graduate
students for their camaraderie. May "epi" take you where you want to go.

I also wish to acknowledge the Michigan equine industry and the MEMS
participants, the Michigan Horse Council, the Michigan Farm Bureau, Michigan
Agricultural Statistics Services, the Michigan Equine Practitioners Association
and the United States Department of Agriculture (APHlS-VS), without their

support and participation, this project could not have been conducted.

 

TABLE OF CONTENTS

LIST OF TABLES ....................................... ix

LIST OF FIGURES ...................................... xii

INTRODUCTION ........................................ 1
Needs Statement ................................... 1
Problem Statement ................................. 3
Objectives ....................................... 4
Overview ........................................ 4

CHAPTER 1

A REVIEW OF RISK FACTORS ASSOCIATED

WITH LAMENESS IN HORSES .............................. 6
Introduction ...................................... 6
Quantification of Lameness ............................ 8
Studies Evaluating Lameness .......................... 12
Risk Factors Associated with Lameness .................. 15
Summary ....................................... 30
Conclusions ..................................... 31

CHAPTER 2

A DESCRIPTIVE EPIDEMIOLOGICAL STUDY

OF LAMENESS IN MICHIGAN HORSES ....................... 33
Abstract ........................................ 33
Introduction ..................................... 35
Materials and methods .............................. 36
Results ......................................... 44
Discussion ...................................... 52

vi

CHAPTER 3
AN OPERATION-LEVEL PROSPECTIVE STUDY OF
RISK FACTORS ASSOCIATED WITH THE INCIDENCE DENSITY

OF LAMENESS IN MICHIGAN (USA) EQUINE OPERATIONS ......... 67
Abstract ........................................ 67
Introduction ..................................... 70
Materials and methods .............................. 71
Results ......................................... 79
Discussion ...................................... 82

CHAPTER 4

AN INDIVIDUAL—ANIMAL—LEVEL PROSPECTIVE STUDY
OF RISK FACTORS ASSOCIATED WITH THE OCCURRENCE

OF LAMENESS IN THE MICHIGAN (USA) EQUINE POPULATION ...... 96
Abstract ........................................ 96
Introduction ..................................... 99
Materials and methods ............................. 102
Results ........................................ 109
Discussion ..................................... 116

CHAPTER 5

SURVIVAL ANALYSIS OF RISK FACTORS ASSOCIATED WITH
THE OCCURRENCE OF LAMENESS IN MICHIGAN (USA) HORSES . . . . 127

Abstract ....................................... 127
Introduction .................................... 129
Materials and methods ............................. 130
Results ........................................ 137
Discussion ..................................... 148

CHAPTER 6

AN EVALUATION OF RISK FACTORS AFFECTING RECOVER FROM

AND DURATION OF LAMENESS IN MICHIGAN (USA) HORSES ..... 158
Abstract ....................................... 158
Introduction .................................... 160
Materials and methods ............................. 161
Results ........................................ 168
Discussion ..................................... 180

SUMMARY, CONCLUSIONS AND FUTURE RECOMMENDATIONS . . . . 187

Summary ...................................... 187

Conclusions .................................... 188

Recommendations ................................ 189
vii

APPENDIX A ........................................ 190

APPENDIX B ........................................ 221

BIBLIOGRAPHY ...................................... 260

viii

Table 1.1:

Table 2.1:

Table 2.2:

Table 2.3:

Table 3.1:

Table 3.2:

LIST OF TABLES

American Association of Equine
Practitioners definition and classification

of lameness (1991). .........................

Mortality Rate (MR), Case Fatality Rate (CFR), and
Weighted Average Annual Incidence Density (AAID) for
incident lameness cases within the Area Affected
categories (Hoof, Leg, Other) and for all incident
lameness cases combined (Total) for 3,925 horses
monitored on 138 equine operations (1992-1994;

Michigan, USA). ............................

Duration and Performance-Days Lost per case for
incident lameness cases within the Area Affected
categories (Leg, Hoof, Other) and for all incident
lameness cases combined (Total) for 3,925 horses
monitored on 138 equine operations (1992-1994;

Michigan, USA). ............................

Lameness Treatment Expenses per case of lameness
(in dollars) for incident lameness cases within the
Area Affected categories (Leg, Hoof, Other) and for

all incident lameness cases combined (Total) for 3,925
horses monitored on 138 equine operations

(1992-1994; Michigan, USA). ..................

Description and descriptive statistics for operation-
management risk factors evaluated for 86 Michigan

equine operations (1992-1994; Michigan, USA). ......

Description and descriptive statistics for environmental
risk factors evaluated for 86 Michigan equine operations

(1992-1994; Michigan, USA). ..................

..45

..45

..83

Table 3.3:

Table 4.1:

Table 4.2:

Table 4.3:

Table 4.4:

Table 5.1:

Table 5.2:

Table 5.3:

 

Multivariable Poisson regression model of operation-

level risk factors associated with the incidence

density of lameness on 86 Michigan equine operations
(1992-1994; Michigan, USA). .................... 85

Description and descriptive statistics for operation-

level risk factors evaluated for 2,330 horses in 97

Michigan equine operations (1992-1994;

Michigan, USA). ............................. 111

Description and descriptive statistics for individual-

animal-level signalment and housing risk factors

evaluated for 2,330 horses in 97 Michigan equine

operations (1992-1994; Michigan, USA). ............ 112

Description and descriptive Statistics for individual-

animal—level activity risk factors evaluated for 2,330

horses in 97 Michigan equine operations (1992-1994;

Michigan, USA). ............................. 113

Multivariable logistic regression model with random

effects of operation- and individual—animal-level risk

factors associated with the occurrence of lameness

in 2,330 horses in 97 Michigan equine operations

(1992-1994; Michigan, USA). ................... 115

Operation and individual-animaI—level signalment and

housing risk factors evaluated for 550 horses in 106

operations participating in the Michigan Equine

Monitoring System, 1992-1994. .................. 142

Individual-animal-level activity risk factors evaluated
for 550 horses in 106 operations participating in the
Michigan Equine Monitoring System, 1992-1994. ...... 143

Multivariable Cox proportional hazards model of

operation and individual-animal-Ievel risk factors

associated with the time to occurrence of lameness

in 550 horses in 106 Michigan horse operations

participating in the Michigan Equine Monitoring

System, 1992-1994. ......................... 147

 

Table 6.1: Total number of lameness cases reported, percent
of cases recovered, and duration per case, within
the Area Affected categories (Hoof, Leg, Other) and
for all lameness cases combined (Total) for 357
lameness cases reported in 89 equine operations
(1992-1994; Michigan, USA). ................... 169

Table 6.2: Total number and percentage of the 3 most common
treatment types in each of the treatment categories
within the Area Affected categories (Hoof, Leg, Other)
and for all incident cases combined (Total) for 357
lameness cases reported in 89 equine operations
(1992—1994; Michigan, USA). ................... 171

Table 6.3: Signalment and activity risk factors evaluated for all
lameness cases combined (Total) for 357 incident
lameness cases reported in 89 equine operations
(1992-1994; Michigan, USA). ................... 173

Table 6.4: Area affected, veterinary diagnosis and treatments
evaluated for all lameness cases combined (Total)
for 357 cases of lameness reported in 89 equine
operations (1992-1994; Michigan, USA). ............ 174

Table 6.5: Multivariable logistic and Cox proportional hazards
regression final models for all lameness cases
combined (Total) for 357 cases of lameness reported
in 89 equine operations (1992-1994; Michigan, USA). . . . 179

xi

Figure 2.1:

Figure 2.2:

Figure 2.3:

Figure 2.4:

Figure 2.5:

LIST OF FIGURES

Page
The proportion (%) of incident lameness cases within
Breed categories (Quarter Horse type (Quarter), Saddle
horse type (Saddle), Standardbreds (SB), Thoroughbreds
(TB), Mixed breeds (Mixed), and Other breeds (OtherI)
from the population of 3,925 horses monitored
(1992-1994; Michigan, USA). .................... 49

The proportion (%) of incident lameness cases within

Activity categories (Breeding (Breed), No specific

activity (NSA), Activities other than Showing or

Racing (Other), Showing (Show), Racing (Race)) from

the population of 3,925 horses monitored on

138 equine operations (1992-1994; Michigan, USA). . . . . 50

The proportion (%) of incident lameness cases within

Exercise categories (None, Low, and High) from the

population of 3,925 horses monitored on 138 equine
operations (1992-1994; Michigan, USA). ............. 51

The proportion (%) of incident lameness cases within

the Racing (Race), Showing (Showing), and Activities

other than showing or racing (Other) categories within

Age categories (0-2 years old, 3-4 years old, 5-8 years

old, and 9+ years old) from the population of 3,925

horses monitored on 138 equine operations

(1992-1994; Michigan, USA). .................... 64

The proportion (%) of Leg, Hoof, and Other

lamenesses (Hip/Shoulder/Back, Generalized, and

No Specific Area categories combined) cases within

Age categories (0-3 years old, 4-7 years old, 8-12

years old, 13+ years old) for 357 incident lameness

cases reported from the population of 3,925 horses

monitored on 138 equine operations

(1992-1994; Michigan, USA). .................... 66

xii

Figure 5.1 :

Figure 5.2:

Figure 5.3:

Figure 6.1:

Figure 6.2:

Figure 6.3:

Univariable hazard ratios (HR) and 95% Confidence

Intervals (error bars) for Activity categories:

non-exercise related activity (Breed), no specific

activity reported (NSA), activity other than showing

or racing (Other), showing (Show), and racing (Race).

* = significantly different (p<0.05) from the Breed

category. .................................. 144

Univariable hazard ratios (HR) and 95% Confidence

Intervals (error bars) for Breed groups: Quarter

Horse types (OHT), Thoroughbreds (THB), Standardbreds

(STB), Saddle Horse types (SDT), Standardbreds, Mixed

(MIX), and Other (OTH). * = significantly different

(p<0.05) from the OHT category. ................ 145

Univariable hazard ratios (HR) and 95% Confidence

Intervals (error bars) for Exercise Levels: No exercise

reported (None), exercise at or below the median for all

horses having an exercise value greater than zero (Low),
exercise above the median score for all horses having a

value greater than zero (High). * = significantly

different (p<0.05) from the None category. .......... 146

Proportion recovered within lameness duration quartiles

for all incident lameness cases combined (Total) for 357
lameness cases reported in 89 equine operations

(1992-1994; Michigan, USA). ................... 175

Proportion of cases requiring veterinary-assisted

diagnosis (Vet Dx) within lameness duration quartiles

for all incident lameness cases combined (Total) for 357
lameness cases reported in 89 equine operations

(1992-1994; Michigan, USA). ................... 176

Proportion of cases receiving treatment within lameness
duration quartiles for all incident lameness cases combined
(Total) for 357 lameness cases reported in 89 equine
operations (1992-1994; Michigan, USA). ............ 177

xiii

INTRODUCTION

"In estimating the importance of this subject [lameness] we have but to
consider that the value of the horse to his human owner must be
measured wholly by his ability to exercise his powers as an agent of
transportation, in the traction of burdens, and in bearing his master’s
person in travel or for pleasure. It becomes then at once apparent that
his capacity for usefulness consists wholly in the condition, as to
efficiency, of his apparatus of locomotion, and his power and will to use
it. The idea of a good horse with poor legs is a misnomer; the legs are
the essence of the horse, and every other part of the equine machine is
of only subservient and tributary importance."

Lameness of Horses and Diseases of
the Locomotory Apparatus
A.F.A. Liautard, 1888
NEEDS STATEMENT
The Michigan Equine Monitoring System (MEMS) was developed because
information about the size of the horse population and its health and economic
status was lacking. This system was a state-wide monitoring system designed
to systematically track the equine population, providing baseline health and
economic information for the equine industry. The MEMS study had 3 primary
objectives: 1) to establish and maintain a data base on the population of
horses, mules, and donkeys in equine operations in Michigan; 2) to identify
major equine disease and health problems based on frequencies and economic
impact of such conditions; and 3) to determine major management and

environmental risk factors that may affect equine health and performance. The

 

 

2

study was conducted in 2 phases. Phase I, completing the first objective,
consisted of an equine census, a description of the types of horses and equine
activities in the state, and an economic description of Michigan equine
operations (Kaneene et al., 1996a). Phase II, the equine health-monitoring
study, focusing on the second and third objectives, has provided information
about equine health problems and about equine operation husbandry practices
and economics (Kaneene et al., 1996b).

Studies have been conducted to describe the types of health problems
reported in the equine industry (Jeffcott et al., 1982; Traub-Dargatz, 1991).
However, few epidemiological studies have been based on prospectively
collected data, multiple breeds of horses and multiple health problems. The
MEMS Phase—ll study population was based on a stratified random sample of
equine operations throughout Michigan, including a representative sampling of
all equine breeds reported in Michigan. Health problem reports included all
cases that were diagnosed by the operator, and or veterinarian, throughout the
course of the study. Furthermore, data were collected prospectively, which
provided an opportunity to evaluate factors to which a horse was exposed prior
to the occurrence of health problems.

The focus of this dissertation is on the epidemiology of lameness in
Michigan horses, based on data from the MEMS Phase-ll study. Lameness was
found to have the highest incidence density and second highest duration and
mortality rate of all health problems reported during the MEMS Phase-ll study

(Kaneene et al., 1996b). Descriptions of the types of horses and the types of

3

lameness affecting horses have been reported. However, many of these
studies were retrospective hospital—based studies dealing with the treatment of
a Specific type of lameness and treatment efficacy or retrospective studies
based on a Specific target population including a single breed (either
Standardbred or Thoroughbred), a single occupation (racing) or a single
environment (the racetrack). Furthermore, few studies have been conducted
that describe the types of lameness problems and potential causative factors
associated with horses performing activities other than racing. Therefore,
additional information about lameness and its causes could be obtained by
conducting a prospective study of the problem focusing on a population of
horses diverse in breeds and activities and placing particular emphasis on the

period prior to racing or performance.

PROBLEM STATEMENT

Population-based epidemiological studies, using prospective monitoring
of the health Status of horses, need to be developed 1) to determine the
incidence of disease in the equine industry; 2) to describe the types of
diseases affecting horses; and 3) to evaluate risk factors associated with the
occurrence of, recovery from, and duration of disease. This type of information
can then be used in the development of strategies to promote the health status

of horses.

 

 

OBJECTIVES

The overall objective of this dissertation is to describe the epidemiology
of lameness in Michigan horses. The specific objectives are: 1) to describe the
magnitude and severity of the lameness problem, the types of losses
attributable to lameness, the types of lameness reported to be affecting horses,
and the characteristics of horses affected by lameness in the Michigan horse
population; 2) to evaluate the associations of operation and individual—animal-
level risk factors with the occurrence of lameness; and 3) to evaluate risk

factors associated with recovery from and duration of lameness.

OVERVIEW

An overview of the entire work is presented here to facilitate
cohesiveness of the dissertation. Chapter 1, a review of the literature,
describes the epidemiological studies of lameness in horses that have been
reported, focusing on the risk factors associated with the occurrence of,
recovery from and duration of lameness. Areas of lameness research that
require further study and how population—based studies may provide a new
dimension to our lameness knowledge base are discussed. Chapter 2 describes
the magnitude and severity of the lameness problem in the Michigan horse
population. This study is unique in that it describes both operator— and
veterinary- diagnosed lameness and the types of lameness cases occurring in
a population of horses diverse both in breed and activity. Chapters 3 and 4

evaluate operation- and individual-animal-level risk factors, using multivariable

5

statistical techniques, that may be targeted for future research in the prevention
of lameness. Chapter 5 evaluates the impact of time-to-lameness, in addition
to operation and individual-animal—level risk factors, using survival analysis
techniques. Chapter 6 describes the types of treatments administered to
horses for lameness in the Michigan horse population and evaluates whether
or not treatment affects recovery rates or duration of lameness.

This dissertation was designed so that individual chapters could be
submitted for publication. Therefore, chapters 2-6 each have their own
introduction, hypotheses, objectives, materials and methods, results, and

discussion sections.

 

Chapter 1

LITERATURE REVIEW OF RISK FACTORS ASSOCIATED
WITH LAMENESS IN HORSES

INTRODUCTION

Impact of lameness on the equine industry

Estimates of annual losses to the United States Thoroughbred industry
attributable to lameness in excess of $250 million (MacKay-Smith, 1979) and
$500 million (Leach and Crawford, 1983) have been reported. Furthermore,
it was suggested that equal levels of loss would be found in all classes of
racehorses, including the Standardbred and Quarter Horse racing industries
(MacKay-Smith, 1979). In England, losses in one season due to keep and
training fees for Thoroughbred horses that did not run were estimated at £37
million, not including costs such as lost stallion fees or mare care (Jeffcott et
al., 1982). Although they are difficult to quantitate, lameness accounts for
other losses to the equine industry including decreased performance levels,
training time lost, loss of prize earnings, and decreased price at time of sale.

Lameness was reported to be the primary cause of wastage in
Thoroughbred racehorses in Great Britain (Jeffcott et al., 1982; Rossdale et al.,

1985). It has also been reported that veterinarians caring for racehorses in the

7

United States estimated that 60-90% of their patients were significantly lame
(Mackay-Smith, 1978). However, the true impact of lameness is difficult to
assess because few population-based studies have been conducted to evaluate
the actual prevalence or incidence of lameness in horses.1 Ultimately, the
occurrence of lameness in horses translates into decreased productivity for
equine operations and the equine industry because individuals are not available
to participate at all or participate at lower-then-expected levels in the activities
for which they are being maintained.

In the livestock industry, most producers are able to rely on a single
commodity, such as meat or milk, to evaluate the impact of health conditions
on productivity. This is not necessarily the case within the equine industry.
The commodity used to assess productivity on an equine operation is the ability
of horses to participate in the specific activities for which they are being
maintained. These activities are diverse across the industry. And, a wide
variety of activities can be found within equine operations. Furthermore,
individual horses may participate in several types of activities at any given time
or over time. Therefore, many types of commodities may be present on a given
operation at a given time, making the assessment of productivity a relatively

complex issue.

 

The term horse will be used to include any of the family of
Equidae including horses, asses, and zebras.

Objective

Because of the diversity of activities and types of lameness reported,
areas that can be targeted for lameness prevention are also diverse. Therefore,
the objective of this paper is to describe the epidemiology of lameness as
presented in the literature. In particular, it will review the methods used to
quantify lameness and the major risk factors associated with the occurrence of,

recovery from, and duration of lameness.

QUANTIFICATION OF LAMENESS

Lameness (an irregularity or defect in the function of locomotion) has
been described as a symptom and manifestation of an underlying physical
lesion (isolated or complicated) which affects the locomotive apparatus
(Liautard, 1888, pp. 7-14; Stashak, 1987, pg. 100). This abnormality of
locomotion affects the ability of horses to perform. Within the equine industry
this decreased ability to perform translates into decreased productivity. Many
different types of lameness, with respect to cause, anatomical location, and
severity, have been reported to affect horses. However, the perception of the
degree and importance of the lameness to the horse owner varies depending
on the activity required of the horse. Therefore, it has been difficult to
establish consistent methods to quantify lameness.

Evaluation of lameness is usually done at the initial diagnosis or when
evaluating post-surgical success. Most studies of equine lameness have

established a grading system to classify lameness by severity. Studies have

 

9

been based on simply whether or not the horse was considered to be lame
(Rossdale et al., 1985). In other studies the lameness has been evaluated
using specific levels of severity (Turner and Tucker, 1989; Steiss et al., 1989;
Wright, 1993; Gaustad et al., 1995; Lillich et al., 1995; Dolvik and Gaustad,
1996). Methods of lameness classification, either lame or not (Eddy and Scott,
1980; Whitaker, 1983; Rowlands et al., 1983, 1985; Faye and Lescourret,
1989; Groehn, 1992; Philipot, 1994; Alban et al., 1996) or by levels of
severity (Phillips, 1990; Moore, 1992; Wells et al., 1993; Mill and Ward, 1994;
Wells et al., 1995; Clarkson et al., 1996; Murray et al., 1996; Phillips, 1990),
have also been used in cattle lameness assessment.

The criteria used to classify cases has been different in many of the
studies reported. For example, one study evaluated lameness based on 10
levels of severity, 0 being the most severe and 6 being sound (Steiss et al.,
1989). In contrast, Wright (1993) used a 10-level scale with 10 being the
most severe and 1 being the lowest level of lameness observed. Another study
reported using an index of lameness based on a combination of the results of
spontaneous lameness and lameness after flexion testing, classification was
based on 6 levels of lameness (Gaustad et al., 1995). Another lameness
classification scheme, defined by the American Association of Equine
Practitioners (1991), is based on 5 levels, or grades, of lameness (Table 1.1).
Development of consistent methods of lameness evaluation will be necessary
to compare the results of studies assessing the impact of lameness on

performance.

10

The individual establishing the diagnosis also differs amongst lameness
studies. Studies have been based on racetrack records or injury reports (Hill et
al., 1986; Speirs et al., 1986; Robinson et al., 1988; Kobluk et al., 1989;
Mohammed et al., 1991, 1992; Laws et al., 1993; Grondahl et al., 1994;
Peloso et al., 1994; Hogan and Bramlage, 1995; Kane et al., 1996; Estberg et
al., 1995, 1996a,b; Jorgensen et al., 1997; Tetens et al., 1997). Racetrack
records provide information about the lameness status of a relatively large
Table 1.1
American Association of Equine Practitioners definition and classification of

lameness (1991).

Definition: Lameness is a deviation from the normal gait or posture due to
pain or a mechanical dysfunction.

Classification Grades:

1. Difficult to observe; not consistently apparent regardless of
circumstances (i.e. weight-carrying, circling, inclines, hard
surfaces, etc.)

2. Difficult to observe at a walk or in trotting a straight line;
consistently apparent under certain circumstances (i.e. weight
carrying, circling, inclines, hard surfaces, etc.)

3. Consistently observable at a trot under all circumstances.
4. Obvious lameness: marked nodding, hitching or shortened stride.
5. Minimal weight-bearing in motion and/or at rest; inability to move.

population. However, they are generally limited to classification of lame or not
and they tend to be evaluated retrospectively. Lameness as diagnosed by a

veterinarian provides more specific information about lameness, including

11

degree of severity and etiology (Turner and Tucker, 1989; Steiss et al., 1989;
Wright, 1993; Gaustad et al., 1995; Lillich et al., 1995). However, only those
cases actually reported to a veterinarian were available for evaluation.
Therefore, the true impact of lameness was not easily assessed. In contrast,
owner or trainer reported lameness provides information about all horses
perceived to be lame within a population, regardless if the lameness was severe
enough to request veterinary assistance with the diagnosis. However, few
studies have been based on owner or trainer diagnosed cases. In most cases,
owner or trainer participation has been in assessing the recovery status of the
horse after lameness treatment (Rossdale et al., 1985; Mcllwraith et al., 1987;
Caron et al., 1990; Mcllwraith et al., 1991; Schneider et al., 1992; Parente et
al., 1993; Platt and Wright, 1993; Kawcak and Mcllwraith, 1994; Vatistas et
al., 1995). This type of reporting is limited in the degree of Specificity or
consistency of diagnosis obtainable. Because of the variability in the quality of
lameness assessment available, the method chosen should be guided by the
objectives of the study being conducted. The development of consistent
methods of lameness evaluation, that can be used by many types of
individuals, will further improve the comparability of study results.

Once lameness has been observed and assessed, it is of interest to
describe the actual factors that predispose horses to lameness and the most
effective therapies returning them to full function. Using this type of

information, effective prevention and therapeutic strategies can be designed to

12

reduce the occurrence of lameness in horses and to improve rates of return to

full function or performance.

STUDIES EVALUATING LAMENESS

Risk factors and the occurrence of lameness

Few epidemiological studies of risk factors associated with the
occurrence of lameness have been reported. Population-based studies of
lameness have been limited largely to a specified population including a single
breed (either Standardbred or Thoroughbred), a single occupation (racing), and
a single type of environment (the racetrack). These studies often use racetrack
records or injury reports, including both retrospective (Jeffcott et al., 1982; Hill
et al., 1986; Mohammed et al., 1991; Mohammed et al., 1992) and
prospective (Rossdale et al., 1985; Stover et al., 1992; Estberg et al, 1993;
Lindner and Dingerkus, 1993; Wilson et al., 1993; Johnson et al., 1994; Peloso
et al., 1994) methods of data collection. Prospective daily monitoring of horses
was used to evaluate the association between exercise level and problem rate
of Thoroughbred horses (Kobluk et al., 1990). Few studies have described
lameness problems experienced by horses performing activities other than
racing (Bell and Lowe, 1986).

These types of descriptive studies have shown that the occurrence and
type of lameness in individual horses may be affected by both intrinsic and
extrinsic risk factors. Intrinsic risk factors investigated have included those

factors related to the characteristics of the individual horse such as its age, sex,

 

13

breed, conformation, and type of injury, among others. Extrinsic risk factors
investigated have included those risk factors found at the individual-animal level
(such as the intensity of exercise or the amount of weight carried during a race)
and those found at the operation- or racetrack-level (such as racetrack design
and racetrack surface). For the most part, these studies have provided
information essential for use in the determination of the types of risk factors
that may contribute to the occurrence of lameness in horses.

However, the strength of the association between these types of risk
factors and the occurrence of lameness may also be evaluated by conducting
analyses which include the risk factors of interest while controlling for
potentially-confounding factors. Few studies have been conducted to evaluate
the association between risk factors and the occurrence of lameness using
multivariable analytical techniques. Mohammed et al. (1991) conducted a
retrospective case-control study using multivariable logistic regression for the
evaluation of intrinsic and extrinsic risk factors associated with injuries in
Thoroughbred horses. Multivariable logistic regression was also used in a
retrospective study to identify the risk of severe (compared to less-severe)
injuries in Thoroughbreds (Mohammed et al., 1992). These study populations
were each limited to Thoroughbred racehorses racing at a specified group of
racetracks in the state of New York (Mohammed et al., 1991; Mohammed et

al., 1992).

14

Risk factors and recovery from and duration of lameness

Even fewer epidemiological studies of risk factors associated with
recovery from and duration of lameness have been conducted. Most studies
have been based on hospital populations (Little and Hilbert, 1987; Caron et al.,
1990; Mcllwraith et al., 1991; Laws et al. 1993; Parente et al., 1993; Wright,
1993; Kawcak and Mcllwraith, 1994; Hogan and Bramlage, 1995; Vastistas
et al., 1995; Tetens et al., 1997), relying on retrospectively collected data from
hospital (Little and Hilbert, 1987; Caron et al., 1990; Mcllwraith et al., 1991;
Laws et al. 1993; Parente et al., 1993; Wright, 1993; Kawcak and Mcllwraith,
1994; Hogan and Bramlage, 1995; Vastistas et al., 1995; Tetens et al., 1997)
and racetrack records (Mcllwraith et al., 1991; Laws et al. 1993; Kawcak and
Mcllwraith, 1994; Hogan and Bramlage, 1995). Many have been conducted
to compare the outcome of a specific lameness treatment to a control
population or to compare the outcome of different treatment methods (Caron
et al., 1990; Laws et al. 1993; Parente et al., 1993; Wright, 1993; Kawcak
and Mcllwraith, 1994; Vastistas et al., 1995).

Evaluation of recovery has been primarily descriptive or based on
univariable analysis of selected factors (Little and Hilbert, 1987; Caron et al.,
1990; Mcllwraith et al., 1991; Laws et al. 1993; Parente et al., 1993; Wright,
1993; Kawcak and Mcllwraith, 1994; Hogan and Bramlage, 1995; Vastistas
et al., 1995). One study used survival analysis techniques, comparing
performance in Standardbreds with tarsocrural osteochondrosis to a control

group, stratifying the data by sex (Laws et al., 1993). Tetens et al. (1997)

15

evaluated race time and performance index with respect to treatment for
midsagittal fractures of the proximal phalanx in Standardbreds using
multivariable analysis of variance, controlling for several potential confounding

factors.

RISK FACTORS ASSOCIATED WITH LAMENESS

The following is a review of both intrinsic and extrinsic risk factors
reported to be associated with the occurrence of, recovery from, and duration
of lameness. The factors described are those commonly reported to be
investigated as potential causative factors.
Intrinsic risk factors
Age

Horses usually enter training for a specific activity between the ages of
2 and 3 years, so, it would be expected that younger animals may be at more
risk of the occurrence of lameness. Younger racehorses were reported to
experience the highest number of fatal injuries (Johnson et al., 1994). And,
Lindner and Dingerkus (1993) reported that the largest proportion of racehorses
experiencing training failure attributable to lameness, infectious disease, and
other causes were 2-year-olds. In contrast, older animals may be at more risk
of experiencing lameness because of the duration of participation in exercise-
related activities and the potential for repetitive type traumatic injury. Studies
within the racing industry have reported that increasing age was associated

with an increase in racing injuries (Mohammed et al., 1991) and severe or fatal

"- ' ‘M~—u- 'L " '

 

 

16

breakdowns (Robinson et al., 1988; Mohammed et al., 1992; Estberg et al.,
1996a). When age was categorized by 2, 3, and 4 + year old groups, both the
2—year-old and 4+—year-old groups had the highest number of performance-
days lost because of lameness (Rossdale et al., 1985). With respect to
laminitis, increasing age was associated with an increase in the risk of
diagnosis of chronic, but not acute, cases (Slater et al., 1995; Polzer and
Slater, 1996).

In contrast, dairy cattle lameness was reported to increase with
increasing age (Rowlands et al., 1985). However, for specific types of
lameness increased age was associated with both increases (white line
abscess, sole ulcers) and decreases (foul-in—the-foot) in specific types of
lameness reported.

Sex

One study reported that there was no influence of gender on the
prevalence of lameness (Dolvik and Gaustad, 1996). In contrast, Slater et al.
(1995) reported that there was an increase in the risk of chronic Iaminitis in
females compared to males. Estberg et al. (1996a) reported that males were
at 2-times the risk of fatal musculoskeletal racing injury compared to mares.
Previous studies have argued that the decreased occurrence of lameness in
fillies during their racing career was associated with the fact that fillies are
more often retired early for breeding purposes--decreasing their risk of exposure

to lameness associated risk factors (Jeffcott et al., 1982; Physick-Sheard,

17
1986a; Physick-Sheard, 1986b; Lindner and Dingerkus, 1993). This may be

the case within the equine industry overall.
Breed

Studies that evaluate lameness across multiple breeds of horses are
lacking. There was a proportionately smaller number of injuries in Quarter
Horses compared to Thoroughbreds at racetracks in the state of California
(Johnson et al., 1994). Different breeds of horses often participate in many
different types of activities. Therefore, it is difficult to use breed alone when
evaluating the types of factors that may predispose horses to lameness. For
example, in the California study, it was suggested that training practices and
gait, rather than breed, may be related to the differences in injury rates
(Johnson et al., 1994).
Other intrinsic factors

Other studies of the impact of intrinsic risk factors on lameness have
focused on genetics, conformation, and parity. It was reported that increasing
sire index (percentage of horses with carpitis within a sire’s progeny group)
was associated with an increased risk of serous carpitis in Norwegian
coldblooded trotters (Dolvik, 1994). Furthermore, Dolvik and Gaustad (1996)
suggested that, based on the results of heritability analysis, horses could be
selectively bred with lameness status in mind. Most studies of the types of
lameness associated with specific conformation have been primarily descriptive
(Beeman, 1973; Stashak, 1987). However, one study did report a trend of

increasing prevalence of laminitis with increasing weight (Cohen et al., 1994).

18

It has been reported that increasing parity was associated with an
increase in the risk of lameness in dairy cattle (Groehn et al., 1992; Wells et al.,
1993). This trend has not been reported for horses. However, it was reported
that foals born at earlier parities were more successful during their racing
careers than those born at later parities (Barron, 1995). Further studies on the
combined effect of genetics and conformation on lameness should be
conducted to evaluate the impact of these factors on racing career success.
Intrinsic factors and recovery from and duration of lameness

For the most part, signalment factors have not been found to be
associated with recovery from lameness. For example, it was reported that age
was not a significant factor affecting post-surgical performance (Mcllwraith et
al., 1991; Hogan and Bramlage, 1995; Vastistas et al., 1995). In contrast,
Wright (1993) reported that older horses were significantly less likely to recover
after surgery for navicular disease. However, it was also reported that the
period of lameness prior to surgery affected the prognosis. Studies have
reported that sex was not a significant factor affecting post-surgical
performance (Mcllwraith et al., 1991). However, it was reported that post-
surgical racing longevity was longer in males than females (Laws et al., 1993).
This may have been a reflection of management and economic decisions
tending to keep males at the racetrack longer and to retire mares for breeding
earlier, rather than of surgical success itself (Jeffcott et al., 1982). Most of the
studies reported have only one breed in the population being evaluated (e.g.

Thoroughbred racehorses). One study did report that, post-surgery, there was

19

no significant difference in return to previous use between Thoroughbreds and
Quarter Horses (Kawcak and Mcllwraith, 1994).
Extrinsic risk factors
Occupation

ActiviguPrevious studies of equine lameness, both hospital-based
(Mcllwraith et al., 1991; Dyson et al., 1992; Schneider et al., 1992; Laws et
al., 1993; Lillich et al., 1995) and population-based (Jeffcott et al., 1982;
Rossdale et al., 1985; Bell and Lowe, 1986; Hill et al., 1986; Kobluk et al.,
1990; Mohammed et al., 1991; Mohammed et al., 1992; Stover et al., 1992;
Lindner and Dingerkus, 1993; Wilson et al., 1993; Johnson et al., 1994; Peloso
et al., 1994; Estberg et al., 1995; Estberg et al., 1996a,b), have reported that
participation in exercise-related activities was associated with an increase in the
occurrence of trauma or stress-related injury and subsequent lameness. The
specific types of activities of horses--racing or non-racing--may affect the types
of lameness reported (Stashak, 1987; Dyson et al., 1992; Dolvik, 1994).
Occupational hazards were reported within the racing industry and indicated
that there were fewer catastrophic injuries per race week for quarter-mile and
harness racing and training than for Thoroughbred racing and training (Johnson
et al., 1994). Dolvik (1994) reported that 2-year old Norwegian coldblooded
trotters that were fast trained or walked in a jog cart were at increased risk of
serous carpitis compared to 2-year olds kept in a paddock. Within the showing
industry, Dyson et al. (1992) reported that hitting a fence while jumping was

the cause of 87% of horses examined for fracture of the medial aspect of the

20

patella. However, because some horses are engaged in several different types
of activities (either simultaneously or throughout time), it can be difficult to
evaluate the impact of a single activity on the occurrence of lameness.

The specific occupation of the horse has not been reported to affect
recovery from lameness. However, it was reported that horses racing prior to
their lameness achieved a significantly higher lifetime race mark and higher
lifetime earnings post-surgery than those who did not (Hogan and Bramlage,
1995). Although there was a relatively high return to racing (86%), horses
raced both prior to and after surgery had slower post-surgical race times and
a decreased performance index (Tetens et al., 1997). Therefore, it is important
to evaluate the definition of recovery with respect to performance. With
respect to race times, this can be relatively easy because of the availability of
racing records. For non-racing types of activities, this is more of a challenge,
because horses can change activities, (e.g. race, change to hunter-jumper), and
be considered recovered, yet they are not performing their originally anticipated
activity.

Exercise--The amount of exercise also appears to be an indicator of the
occurrence of lameness. An increase in the incidence of lameness was
reported in Thoroughbred racehorses in the month of March--directly correlated
with the beginning of more-intensive race training (Lindner and Dingerkus,
1993). Estberg et al. (1995) reported that excessive rates of accumulation of
racing-speed distances increase the risk for racing and race-training fatal

musculoskeletal injury in Thoroughbred racehorses. In another study, Estberg

21

et al. (1996b) reported that high total and average daily rates of exercise
distance accumulation within a 2—month period were associated with higher
risks for fatal musculoskeletal injury during racing. Dolvik (1994) found that
the risk of serous arthritis in the carpal joint of Norwegian coldblooded trotters
was increased if exposed to walking in a jogcart and fast training versus being
left in a paddock in the 2-year-old year. Physick-Sheard (1986a) reported that
the slower rate of attrition observed for trotters was reflected in their longer
racing life, and may partly be explained by the generally less-intensive career
of trotters compared with pacers.

In contrast, Kobluk et al. (1990) reported a negative linear relationship
between exercise score and problem score of racing Thoroughbreds: horses
with fewer musculoskeletal problems were exercised harder and higher-quality
horses clustered in the high exercise-low problem score areas. Kobluk et al.
(1990) concluded that these types of relationships were consistent with their
observation that trainers used injury levels in making decisions about training
programs for horses. Mohammed et al. (1991) reported a negative association
between the number of seasons racing, the number of starts per year, and the
total number of starts. This again may have indicated that healthier horses
were participating in racing activities at increased levels. The ability of trainers
to utilize preventive tactics against lameness may have affected the amount of
exposure individuals had to exercise-related activities (intensity of exercise) and

their subsequent risk of lameness.

22

Ultimately, what may be most important is the type of activity (e.g.
movement required) and the amount of activity combined to produce a situation
that predisposes horses to injury. For example, it was reported that preexisting
conditions, such as stress fractures, predisposed racehorses to severe
musculoskeletal injuries (Stover et al., 1992). It has been reported that
increased duration of training significantly enlarges the dorsopalmar metacarpal
bone diameter, cortical area and area moment of inertia, but not bone breaking
strength (Sherman et al., 1995). Therefore, the development of specialized
training regimes, such as interval training (Harkins et al., 1990), may reduce the
occurrence of racing injury by reducing preexisting training-related injury. In
one study, swimming was introduced into a conventional training protocol for
young horses (Misumi et al., 1994). These investigators reported that this
training protocol reduced the vulnerability of horses to locomotor diseases while
providing favorable results with respect to training.

Fatigue has also been suggested to be associated with the occurrence
of lameness. However, few studies have evaluated this as a specific risk
factor. Hill et al. (1986) reported that there was no association between length
of race and racing injuries (fractures and soft tissue) to Thoroughbred horses.
Mohammed et al. (1992) reported that horses were more likely to experience
severe injury in the early part of the race ($6 furlongs) than the latter part of
the race (>6 furlongs). In contrast, Rooney (1982) predicted that lameness
could be reduced by about 14% and bone-fracture breakdown by 24% if longer

race distances were eliminated.

23

Environment

Footinq and beddinq--Environmental conditions (such as the stall flooring
and bedding) may be associated with equine lameness as they are associated
with dairy-cattle lameness. For example, in dairy cattle, cement flooring has
been reported to be associated with lameness (Rowlands et al., 1983; Faye and
Lescourret, 1989). It was also reported that decreased thickness of straw
bedding was associated with an increased occurrence of lameness (Faye and
Lescourret, 1989; Philipot et al., 1994). Furthermore, the methods and
frequency of stall sanitation have also been reported to be associated with
increased lameness (Philipot et al., 1994).

Within the equine industry, few studies have evaluated the impact of
environment on the occurrence of lameness. One study reported that there
was no significant difference in behavior of horses bedded on straw, wood
shavings, or shredded plastic (Thompson, 1995); however, no associations
with lameness were investigated. Exposure of horses to black walnut shavings
were implicated in case reports of epizootics of laminitis from several stables
(True et al., 1979).

Exercise surfaces--Exercise surface, in particular racetrack conditions,
have been the major focus of study on how the environment may predispose
horses to lameness. Tests of the mechanical behavior of racetrack surfaces
have been conducted (Cheney et al., 1973; Pratt, 1985; Zebarth and Sheard,
1985; Clanton et al., 1991 ). Studies of the correlation between lameness and

specific racetrack conditions have been reported (Cheney et al., 1973;

24
Fredericson et al., 1982; Clanton et al., 1991). Cheney et al. (1973) concluded

that tracks with a pliant, soft base and a loose cushion could drastically reduce
the dynamic impact on a running Thoroughbred racehorse, thus minimizing the
occurrence of lameness in such horses during races. It was the opinion of
trainers and riders that a hardwood fiber racetrack created improved conditions
for the training and racing of Thoroughbreds (Fredericson et al., 1982). Other
studies have focused on the ergonomics of the design of the racetrack itself.
These researchers used cinematographic recordings of the actions of trotters
moving in curves, and from this have indicated how racetrack design changes
may reduce the incidence of lameness in racehorses (Dalin et al., 1973;
Fredericson et al., 1975a,b).

Studies based on records of race performance and injury reports have
reported conflicting results with respect to the importance of track condition.
No association was reported between racing injuries and the type of track (dirt
or turf) (Hill et al., 1986; Robinson et al., 1988), the track condition and the
location of injury occurrence on the track (Hill et al., 1986). In contrast, other
studies have reported a significant association between the risk of breakdown
and the track involved and its condition (i.e. horses raced at one track when it
was muddy were at increased risk of injury compared to another track in dry
conditions) and the track type (i.e. there was a reduced risk on turf than dirt)

(Mohammed et al., 1991; Mohammed et al., 1992).

25

Management

Operation size--When evaluating risk factors associated with lameness
in the dairy industry, operation size has been used as a factor to control for the
level of management and the operator’s knowledge of disease diagnosis,
treatment, and preventive health care. Rowlands et al. (1983) reported a
negative relationship between herd size and the incidence density of lameness
in dairy cattle. In contrast, Faye and Lescourret (1989) reported a positive
relationship between herd size and the incidence of lameness. And, Groehn et
al. (1992) reported that medium sized herds (between 50—99 cattle) were at
increased risk for lameness. Because few operation—, or herd—, based studies
have been conducted in equine populations, the association between herd size
or management has not been evaluated in detail. In light of the variability of
findings in the dairy industry and the diversity of horses and activities within
equine operations, compared to dairy herds, the use of this factor as an
indicator of management should be examined carefully.

Veterinary services--lt is generally understood that prevention of
lameness is important and that improvement of health management practices
can be a means to reduce the occurrence of lameness. However, use of
veterinary—related services by operators may be influenced by the type and
amount of activity to which their horses are exposed. Operations that have
horses participating in training activities may be more apt to diagnose a
lameness case and to be more knowledgeable of the importance of veterinary

care to their operation. In the dairy industry, it has been reported that the

26

prevalence of lameness was negatively correlated with the knowledge, level of
training and awareness of the farmers (Mill and Ward, 1994).

Few studies have been conducted in the equine industry to evaluate the
association between routine veterinary care and the occurrence of lameness.
For some conditions, however, the association between diagnostic findings and
the occurrence of lameness must be critically evaluated. For example, Grondahl
et al. (1994) reported that there was no difference in earnings after the racing
season as 3- and 4-year olds between horses with radiographic changes in the
proximal sesamoid bones and those without such changes.

Farrier services--Again, it is generally understood that routine farrier care
for horses is a means of reducing the occurrence of lameness. And again, the
use of farrier-related services may be related to the type and amount of activity
to which horses are exposed and the knowledge level of the operator. The
importance of regular hoof trimming at pasture was reported to have a positive
effect on hoof health in dairy cattle (Faye and Lescourret, 1989). In contrast,
a positive association between regular hoof trimming practices and the total
frequency of hoof diseases was also reported (Faye and Lescourret, 1989).
This positive association may actually have been attributable to increased
diagnosis on those farms using farrier services.

Although few studies have been reported that quantitatively evaluate the
association between hoof care and lameness, those that have been reported
suggest that farrier intervention may have an effect on the occurrence of

lameness. Kobluk et al. (1989) reported that a lower hoof angle was correlated

27

with a higher lameness problem score and that horses with >10 lifetime wins
had higher hoof angles than those with <10 lifetime wins. Kane et al. (1996)
indicated that appliances of the horse shoe may be associated with lameness.
In this study, toe grabs were identified as a possible risk factor for fatal
musculoskeletal injury, suspensory apparatus failure and cannon bone condylar
fracture. In contrast, rim shoes were associated with one-third of the risk of
fatal musculoskeletal injury or suspensory apparatus failure.

Nutrition—-Most studies in the field of nutrition are experimentally-based
studies focusing on the influence of a specific nutritional factor. For example,
Josseck et al. (1995) reported improvement of hoof wall quality with biotin
administration using a double blind, placebo controlled clinical trial. Few
epidemiological studies have been conducted to evaluate a link between a
specific nutritional factor or diet type to the occurrence of lameness. An
aggregate-risk study provided support for an association between horses
exposed to endophyte-infected tall fescue and an increase in the risk of
laminitis; however, it was stated that studies at the individual level would have
to be conducted to confirm the hypothesis (Rohrbach et al., 1995). A
population-based cross-sectional study evaluating feeding regimes during the
first, second, and third year of life in Norwegian coldblooded trotters revealed
no association between diet and the occurrence of carpitis (Dolvik, 1994).

Osteochondritis dessicans is a nutritionally-related disease of horses.

However, the exact etiology of the disease and its impact on lameness has not

been determined. It is noteworthy, that one study found that there was no

 

 

 

 

 

 

 

 

 

 

 

 

28

association between the presence or type of radiological abnormalities
associated with osteochondritis dessicans and the subsequent performance and
longevity of racehorses. Horses with multiple lesions, however, had a tendency
to lower earnings and poorer survival than horses with single lesions (Storgaard
Jorgensen et al., 1997). Therefore, assessment of the importance of this
disease with respect to lameness may be overestimated if diagnostic testing
without lameness evaluation is conducted.
Treatment

Most studies of recovery from lameness are based on comparing the
success of different lameness treatment methods using various study designs.
Experimental studies evaluating the effectiveness of medications in reducing
lameness symptoms have been reported (Gausted and Larsen, 1995; Owens
et al., 1995; Owens et al., 1996). Clinical trials to evaluate the degree of
lameness after administration of specific drug, such as isoxsuprine
hydrochloride for the treatment of navicular disease (Rose et al., 1983; Turner
and Tucker, 1989), or therapy, such as electroacupuncture for the treatment
of chronic lameness in horses and ponies (Steiss et al., 1989), have been
reported. One hospital-based study reported that the proportion of horses
developing laminitis among those that received heparin was significantly less
than among those that did not (Cohen et al., 1994).

Clinical studies of the success of surgery, based on post-surgical
performance have been reported. Recovery, usually evaluated as ability to

return to performance, was reported to have occurred in 59% (Parente et al.,

29
1993), 65% (Caron et al., 1990), 76% (Mcllwraith et al., 1991) and 89%

(Tetens et al., 1997) of horses treated. None of the studies reported that
horses returned to performance at higher levels than prior to their surgery. In
fact, most of the studies reported a decrease in performance levels based on
total races and number of wins (Speirs et al., 1986; Laws et al., 1993), and
race time and performance index (Tetens et al., 1997). However, there was
no difference in performance based on earnings (Speirs et al., 1986; Laws et
aL,1993L

Few population-based studies have been conducted in the equine
industry to assess the rate or impact of lameness treatment on recovery from
and duration of lameness. Studies in the dairy industry suggest that the overall
incidence of lameness reported in the industry is affected by whether or not the
farmers records were included in lameness case identification. For example,
Whitaker et al. (1983) reported that the average veterinary treatment rate for
lameness was 6.3% while 18.7% of cases were treated by farmers, indicating
that the true overall incidence of lameness was higher than previously reported.
Murray et al. (1996) also indicated that veterinarians treated 32% of the
lameness cases and farmers and stockmen an additional 46% of the lameness
cases. One study reported evidence that training farmers to recognize early
cases of lameness and to request veterinary treatment resulted in a marked
reduction in the lameness case duration (Clarkson et al., 1996). These
principles may hold within the equine population and should be evaluated in

more detail.

30
SUMMARY

Throughout the equine industry, evaluation of risk factors associated
with the occurrence of lameness in horses can be difficult due to the diversity
in types of horses and equine operations. Differences in operation management
and operation environment vary between operations. Differences in the breeds
of horses and their specific occupations vary not only between operations, but
within operations. Variations in individual occupations will affect the types of
lameness cases, their severity and complexity, being evaluated. This may
account for some disagreement in the results of different studies.

The true impact of lameness on the equine industry is still not well
understood. This is primarily because most studies have focused on hospital
populations or are limited to studies within the racing industry. These studies
often lack the external validity necessary to assess the true magnitude of the
lameness problem in the horse population. Limitations in knowledge about the
factors predisposing horses to lameness exist because most studies are
conducted after the lameness has already occurred. Because any information
about the lameness diagnosis or the management and environment to which
the horse was exposed prior to the lameness must then be collected
retrospectively, accurate or sufficiently detailed information may be lacking.
Assessment of lameness treatment effectiveness is difficult because few true
clinical trials are reported in the literature. Most studies of treatment efficacy
been based on retrospectively collected hospital records or on experiments

having relatively small sample sizes.

31
CONCLUSIONS

Epidemiological studies may be able to address some of limitations in
equine lameness research. Population-based studies, developed using proper
sampling techniques and study design, would help to provide a more accurate
and valid assessment of the impact of lameness on the equine industry.
Furthermore, prospective monitoring of horses would allow for more detailed
evaluation of risk factors that predispose horses to different types of lameness,
especially prior to performance (e.g. during training and conditioning).

Identification of risk factors predisposing to lameness provides a basis
for the development of lameness prevention methods and a mechanism for the
veterinary profession to participate in reducing, rather than just treating,
lameness. As an extension of the experimental studies of lameness treatment
effectiveness, population-based clinical trials would help to improve the
generalizability of the results. Population-based epidemiological studies are not
without their challenges, however. Prospective studies, in particular, are time
and labor intensive. Therefore, study design must be able to accommodate the
objectives desired within a reasonable time frame, sometimes at the expense
of more detailed information.

Future population-based studies should continue to be developed to
provide another base of information on how to reduce the occurrence of
lameness and improve recovery rates in the equine industry. Specifically,
studies should focus on the incidence of different types of lameness occurring

within the industry as a whole and within subpopulations of interest. Further

32

evaluation of the association of occupation, training, veterinary and farrier
methods used, work surface exposure, and nutritional management should
identify, more specifically, risk factors that can be targeted for lameness
prevention. More accurate methods to evaluate the severity and complexity of
lameness cases (e.g. biomechanical techniques) should be developed to
quantify the effectiveness of specific lameness treatments, whether or not the
horse made a full recovery, and whether it was within an adequate amount of
time. Ultimately, any information that can provide the equine industry and the
veterinary profession with a means to reduce the occurrence of lameness and
to improve recovery rates will help to reduce productivity losses associated

with lameness.

Chapter 2

A DESCRIPTIVE EPIDEMIOLOGICAL STUDY OF LAMENESS
IN MICHIGAN HORSES

ABSTRACT
Objectives--To describe the magnitude and severity of the lameness problem,
the types of losses attributable to lameness, the types of lameness reported to
be affecting horses, and the characteristics of horses affected by lameness in
the Michigan horse population.
Design--Prospective cohort study design.
Study population-~The study population included 3,925 horses from 138
randomly selected equine operations throughout Michigan.
Procedure-During two 12-month rounds of data collection, inventory, health,
activity, and economic data were collected prospectively for all horses in each
operation participating in Phase II of the Michigan Equine Monitoring System
study. Data were summarized and descriptive statistics were computed.
Results--The Period Prevalence of lameness was 26.7 lame horses per 100
horses monitored. The Mortality Rate, Case Fatality Rate, and the Average
Annual Incidence Density of lameness were 1.0, 2.9, and 16.0 per 100 horses

monitored, respectively. The average duration of an incident and a prevalent

33

34

case of lameness was 43.1 days and 144.3 days, respectively. It cost
operators an average of $58.00 to treat a case of lameness and the Lameness
Cull Percentage was 29%. Leg-associated lameness, not including the hoof,
accounted for 42% of the incident lameness cases reported, followed by Other
types of lameness (31%), and Hoof-associated lamenesses (27%). Within the
study population, a significant difference (p30.05) in the distribution of
lameness cases between individual horse characteristic categories was found
for Sex (p =0.001), stallions and geldings had a higher proportion of lameness
cases than did mares; Registration (p=0.05), registered horses had a higher
proportion of lameness cases; Activity (p=0.001), more exercise intensive
types of activity had higher proportions of lameness cases; and Exercise
(p = 0.001 ), increasing amounts of exercise had higher proportions of lameness
cases.

Clinical implications--Development of improved methods of lameness prevention
should focus primarily on Leg lameness, not including the hoof, especially in
younger horses. As horses age, the focus should be modified to include Hoof
and Other types of lameness. The impact of lameness on horse populations
should be evaluated with respect to the age, sex, type of activity, and amount

of exercise.

35
INTRODUCTION

Lameness was found to have the highest incidence density of all health
problems reported in horses1 during the MEMS Phase-ll equine health-
monitoring study (Kaneene et al., 1997b). Descriptions of the types of horses
and the types of lameness affecting horses have been reported. However,
many of these studies were retrospective hospital-based studies dealing with
the treatment of a specific type of lameness and treatment efficacy (Mcllwraith
et al., 1991; Laws et al., 1993; Vatistas et al., 1995) or studies based on a
specific target population including a single breed (e.g. Standardbred or
Thoroughbred), a single occupation (racing), or a single type of environment
(the racetrack) (Robinson et al., 1988; Mohammed et al., 1991, 1992; Stover
et al., 1992; Johnson et al., 1994; Peloso et al., 1994; Estberg et al., 1996).
Furthermore, few studies have been conducted that describe the types of
lameness problems and potential causative factors associated with horses
performing activities other than racing (Bell and Lowe, 1986). In contrast, the
MEMS Phase II was designed as a prospective cohort epidemiological study to
evaluate all types of health problems, including lameness, in a diverse
population of horses, activities, and operation environments.

The objective of this study was to describe the magnitude and severity

of the lameness problem, the types of losses attributable to lameness, the

 

1 The term horse will be used to include any of the family of
Equidae including horses, asses, and zebras.

36

types of lameness reported to be affecting horses, and the characteristics of

horses affected by lameness in the Michigan horse population.

MATERIALS AND METHODS

Study Design-Details of the design and implementation of the MEMS
study, Phases 1 and II, have been published (Kaneene et al., 1997a). The
MEMS Phase-ll data base was used for the purposes of this investigation.
Details of data-collection methods used for the MEMS Phase-ll equine health-
monitoring study have been published (Kaneene et al., 1997b). Briefly, the
equine health-monitoring study was designed as a prospective epidemiological
study. Equine operations, whose operators consented to participate, were
enrolled in the study for 12 months.

Participating operators were interviewed on a monthly basis by a state,
federal, or university veterinarian or animal technician (a MEMS data collector).
Data regarding operation management, operation environment, and other
information not expected to change on a monthly basis were collected at the
beginning (initial management surveys) and at the end of the study (close-out
survey) (see Appendices A and B). Equine health status and activities, and
operation economic data were expected to change on a daily basis. These
types of data were recorded by operators throughout each month of data
collection (see Appendices A and B). On a monthly basis, the MEMS data
collector for each operation interpreted, summarized, and recorded these data

on data-collection instruments specifically designed for data entry.

37

Definition of a case-- For the purposes of this study, a horse was
considered to have a case of lameness if it was reported to have a condition
causing abnormal locomotion in one or more gaits or a problem with
locomotion-associated anatomical structures. Determination that a horse was
lame, the description of the specific type of lameness affecting the horse, and
recovery from lameness was made by the operation owner, veterinarian,
trainer, or farrier and reported to the MEMS data collector. Detailed information
about lameness diagnostic techniques used was not available. Confirmation of
diagnoses was not conducted.

Horses that had a lameness problem at the beginning of the study or at
the time of entry into the study population were considered to have a prevalent
case of lameness. Horses that experienced a lameness problem during their
monitoring period were considered to have an incident case of lameness.
Horses may have experienced more than one incident case of lameness during
the study period, either simultaneously or sequentially.

Statistical analysis--Specific information about individual horses was
summarized from the monthly data-collection instruments. The horse-day,
representing each day a horse was monitored during the study period, was the
unit of observation. The total number of horse-days monitored for an individual
horse was the total number of days monitored between the date of entry into
the study population and the date of exit. When a horse left the operation
during the study and then returned, the days off of the operation were not

included in the total horse-days monitored

 

 

38
The Period Prevalence (PP), Mortality Rate (MR), and Case Fatality Rate

(CFR) of lameness were computed as shown in equations 1, 2, and 3,
respectively.
Period Prevalence (PP)
= (Lame Horses / Average Population per Day) x 700 (Eq. 1)
Mortality Rate (MR)
= (Lameness Deaths / Average Population per Day) x 700 (Eq. 2)
Case Fatality Rate (CFR)
= (Lameness Deaths / Lameness Cases) x 700 (Eq. 3)
where
Lame Horses
= total number of horses with at least one case of lameness reported
(prevalent or incident case) during the 2-year study period
Average Population
= average number of horses in the study population per day during the
2-year study period
=(814,753 total horse-days monitored during the study period) l (365
+ 366 study days in rounds I and 2, respectively)
Lameness Deaths
= total number of horses that died because of causes associated with

a lameness case (prevalent or incident) during the 2-year study period

39

Lameness Cases
= total number of lameness cases (prevalent or incident) reported during
the 2-year study period
The force of morbidity of lameness in the study population was described using
the weighted average annual incidence density (AAID) as computed by Kaneene
et al. (1997b).
The duration of lameness and the performance-days lost because of
lameness were evaluated using equations 4 and 5, respectively.
Duration = (Horse-Days Lame / New Lameness Cases) (Eq. 4)
Performance-0a ys Lost
= (Days Lost/ New Lameness Cases) (Eq. 5)
where
Horse-Days Lame
= total number of horse-days affected by lameness during the
study period
New Lameness Cases
= total number of incident lameness cases reported during the
study period
Days Lost = total number of days that the horse could not exercise/perform
because of an incident case of lameness during the study period
Horses could experience more than one case of lameness during the study
period and cases of lameness could occur simultaneously. When this occurred,

one horse-day lame or performance-day lost was assigned for each lameness

 

40

case reported. Therefore, when computing Horse-Days Lame and Days Lost,
if a horse experienced simultaneous cases of lameness, one horse—day or one
performance-day lost was included for each of the lameness problems reported
on that day, respectively. Because information about the duration of the case
and associated days lost prior to entering the study were not available, the
duration and performance-days lost for prevalent cases were considered to be
underestimated, and therefore, were not described in detail.

The treatment expense per incident case of lameness (in dollars) was
computed for the professional fees assigned to the diagnosis and treatment of
lameness by a veterinarian, for professional fees assigned to the diagnosis and
treatment of lameness by a farrier, for the cost of drugs administered by or
purchased from a veterinarian, for the cost of drugs purchased and
administered by the owner or manager, and for all expenses combined. The
labor hours reported to have been devoted to treatment of the lameness case
were also summarized. The expenses for prevalent cases were not described
because information about the duration of the case and associated expenses
prior to entering the study was not available. It is important to note that the
economic data summarized here do not include farrier expenses for prevention
of lameness, expenses for the use of drugs on hand, labor expenses, or
expenses attributable to death of the horse or loss in value at the time of sale.
Although monetary expenses attributable to culling were not reliably available,

culling attributable to lameness was described using equation 6.

41

Lameness Cull Percentage = Lameness Cul/s / Any Disease Cul/s (Eq. 6)

where

Lameness Culls = total number of horses that were sold or that exited the
operation because of a lameness case (prevalent or
incident) during the study period

Any Disease Culls = total number of horses that were sold or that exited the
operation because of a case of any type of disease problem
(prevalent or incident) during the study period

For descriptive purposes, the types of lameness reported by operators

were placed into 3 general Area Affected categories: 1) Hoof, including

lameness reported to be attributable to problems associated with structures of

the hoof, 2) Leg, including lameness reported to be attributable to extremity-

associated problems other than hoof problems and 3) Other, including

lameness reported to be attributable to back and pelvic-associated structures,

lameness with no specific regional association (e.g. exertional myopathy), or

lameness with an undetermined or unspecified etiology. The MR, CFR, AAID,

Duration, Performance-Days Lost, Treatment expenses, Labor hours, and

Lameness Cull Percentage were computed for lameness within each of the Area

Affected categories.

The specific types of lameness were described by computing the
proportion of cases diagnosed with the involvement of a veterinarian, the
proportion of prevalent and incident lameness cases reported during the study

period, and the proportion of horses experiencing multiple cases of lameness.

42

To describe the types of lameness cases in more detail, the proportion of
lameness cases reported to have been affecting a specific body region (Area
Affected categories) were computed.

Differences in the distribution of lameness within the study population
for several individual horse characteristics were evaluated using the Mantel-
Haenszel Chi-square or the Fisher’s 2-tailed exact test where appropriate. The
following is a description of the individual horse characteristics evaluated and
how they were categorized. The season when the lameness was reported to
have occurred was categorized by Winter (December-February), Spring (March-
May), Summer (June-August), and Fall (September—November). The type of
housing while on the operation was categorized by: Inside only, Both
inside/outside, Outside only. Signalment information included the age
(categorized by 0-3 years old, 4-7 years old, 8—12 years old, and 13+ years
old), sex (Mare, Stallion, Gelding), breed (grouped by general phenotype
including Quarter Horse type (including Quarter Horses, Appaloosas, and Paints,
etc.), Saddle type (including Arabians, Morgans, and Saddlebreds, etc.),
Standardbreds, Thoroughbreds, Mixed breeds (including Warmbloods and part-
breds such as Half-Arabians, Thorcherons, etc.), and All other breeds (including
Draft horses, Ponies, and Grade horses, etc.)), and whether or not the
individual was registered with a breed or color association. The occupation of
horses was summarized in two stages because many horses were reported to
have participated in more than one activity during the study period. First,

eleven different activity groups were constructed from the data and horses

43

were assigned to each one in which they were reported to have participated in
or not (breeding, conditioning, draft, dressage, driving, hunter, flat racing,
harness racing, pleasure riding, showing, and western). Finally, these groups
were collapsed into five mutually exclusive activity groups expected to show
exposure to more exercise intensive types of activity: Breeding, Activity not
reported, Activities other than racing or showing, Showing, Racing.

The amount of exercise or performance—related activity to which a horse

was exposed, was described by equation 7.

Exercise = Total Work-Days / (Total Horse-Days - Days Lost) (Eq. 7)
where
Total Work-Days = total number of days the horse was reported to have

been exercised and or to have performed during the study
penod
Total Horse-Days = total number of horse-days that the individual was
monitored during the study period
Days Lost = total number of exercise or performance days the
individual lost because of lameness during the study period
Exercise was then categorized for analysis. Three categories of exercise were
created: None (horses having a value for exercise of zero), Low (a value for
exercise at or below the median score for all horses having a value greater than
zero), and High (a value for exercise above the median score for all horses

having a value greater than zero).

44

Within the lame horse population, the Fisher’s 2-tailed-exact test or the
Mantel-Haenszel Chi-square test was then used, where appropriate, to
determine if there were any significant differences in the distribution between
each of the individual horse characteristics evaluated and the Area Affected

categories.

RESULTS

The study population--A total of 138 Michigan equine operations
participated in the MEMS Phase-ll equine health-monitoring study, 77 in round
I and 62 in round ll of data collection The total number of horses monitored in
these two 12-month rounds of data collection was 3,925 (Per operation:
Minimum (Min) = 1; 2nd Quartile (O) =6; Median (Med) =14; 3rd O=34;
Maximum (Max)=423) with an accumulated total horse-days monitored of
814,753 (Per operation: Min =116; 2nd O=1,417; Med =2,584; 3rd
O=7,899; Max=58,964). The median number of horse-days monitored per
horse was 214 (Min=1; 2nd 0:59; 3rd 0:365; Max:366).

Magnitude and severity of lameness--The PP of lameness was 26.7 lame
horses per 100 horses monitored per day. The area specific and total MR, CFR,
and AAID per 100 horses monitored during the 2-year study period are found
in Table 2.1.

Losses attributable to lameness--The area specific and total duration and
performance-days lost per case of lameness are found in Table 2.2. The

duration per case of a prevalent lameness was 144.3 days (Min =1, 2nd

45

Table 2.1

Mortality Rate (MR), Case Fatality Rate (CFR), and Weighted Average Annual
Incidence Density (AAID) for incident lameness cases within the Area Affected
categories (Hoof, Leg, Other) and for all incident lameness cases combined
(Total) for 3,925 horses monitored on 138 equine operations (1992-1994;
Michigan, USA).

 

 

MR' CFR' AAID'
Hoof 0.1 0.3 4.3
Leg 0.4 1.0 6.5
Other 0.5 1.6 4.9
Total 1.0 2.9 16.0

 

' MR, CFR, and AAID reported per 100 horses monitored.

Table 2.2

Duration and Performance—Days Lost per case for incident lameness cases
within the Area Affected categories (Leg, Hoof, Other) and for all incident
lameness cases combined (Total) for 3,925 horses monitored on 138 equine
operations (1992-1994; Michigan, USA).

 

Per Case n Mean Mina 2nd Qb Median 3rd 0" Maxc

 

 

 

 

Duration

Hoof 96 45.3 1 6 22 44 352

Leg 149 35.6 1 5 15 32 360

Other 112 51.2 1 4 18 51 290
Total 357 43.1 1 5 18 45 360

Performance-De ys Lost

Hoof 96 1 1.4 0 0 0 9 275

Leg 149 6.2 0 0 O 6 61

Other 1 12 8.5 0 0 0 8 101
Total 357 8.3 0 0 0 7 275

 

a Minimum. b Quartile. ° Maximum.

 

46
Q = 26, Med = 46, 3rd Q = 35, Max = 366). The average performance-days lost

per prevalent case of lameness was 7.8 days (Min =0, 2nd Q =0, Med =0, 3rd
Q =10, Max = 43). Table 2.3 shows area specific and total treatment expenses
per incident lameness case. Treatment time per case of lameness was 3.5
labor hours. Per case, Hoof lameness treatment required 6.1 labor hours, Leg
lameness required 3.0 labor hours, and Other types of lameness required 2.0
labor hours. The Lameness Cull Percentage was 29.1% (16/55). Eleven of 16
(68.8%) horses were culled for Other types of lameness, 3 of 16 (18.8%) were
culled for Leg-associated lameness, and 2 of 16 (12.5%) were culled for Hoof-
associated lameness.

Table 2.3

Lameness Treatment Expenses per case of lameness (in dollars) for incident
lameness cases within the Area Affected categories (Leg, Hoof, Other) and for

all incident lameness cases combined (Total) for 3,925 horses monitored on
138 equine operations (1992-1994; Michigan, USA).

 

 

 

Area n Treatment Expenses per Case ($I
Affected Vet Far Vet Own Total
Feesa Feesb Drug° Drugd Expe
Hoof 96 34.43 1.66 5.51 8.37 49.97
Leg 149 39.40 0.17 11.78 5.82 57.17
Other 112 36.45 1.03 20.89 8.34 66.71
Total 357 37.14 0.84 12.95 7.30 58.23

 

a Professional fees assigned to the diagnosis and treatment of lameness by a
veterinarian. b Professional fees assigned to the diagnosis and treatment of
lameness by a farrier. ° The cost of drugs administered by or purchased from
a veterinarian. d The cost of drugs purchased and administered by the owner
or manager. ° All expenses combined.

47

Lameness cases reported--A total of 382 cases of lameness were
reported for 298 horses monitored in 92 operations during the study period.
A veterinarian was associated with the diagnosis in 213 of 382 (55.8%)
lameness cases reported. A prevalent lameness case only was reported for 18
of 298 (6.0%) lame horses. An incident lameness case only was reported for
274 of 298 (91.9%) lame horses. Of the 280 horses reported to have
experienced an incident case of lameness, 225 (80.4%) had a single case, 38
(13.6%) had 2 cases, 14 (5.0%) had 3 cases, 1 (0.4%) had 4 cases, and 2
(0.7%) had 5 cases. Simultaneously occurring lameness cases were reported
for 17 of the 298 (5.7%) lame horses.

Of the 357 incident cases of lameness reported, 96 (26.9%) were
reported to be Hoof-associated lamenesses, 149 (41.7%) were reported to be
attributable to Leg-associated lameness, not including the hoof, and 112
(31.4%) were reported to be a attributable to Other types of lameness. Of the
96 cases within the Hoof category, 30 (31.25%) were reported to be
attributable to punctures or sole bruises, 12 (12.50%) were reported to be
attributable to laminitis, and 7 (7.3%) were reported to be attributable to
navicular syndrome. Of the 149 cases within the Leg category, 31 (20.8%)
were reported to be attributable to the cannon bone region, 20 (13.4%) were
reported to be attributable to the hock, 19 (12.8%) were reported to be
attributable to the fetlock and pastern region, 15 (10.1%) were reported to be

attributable to the carpus, 7 (4.7%) were reported to be attributable to the

48

stifle, and 53 (35.6%) were reported to be attributable to problems of the leg,
yet no specific region was indicated.

The types of lameness reported to be associated with the cannon-bone
region included 20 of 31 (64.5%) lameness cases attributable to problems with
tendinous structures (e.g. bowed tendons) and 4 of 31 (12.9%) lameness
cases attributable to problems with the cannon bone itself (e.g. bucked shins).
Within the Other lameness category, information was lacking that could
categorize the lameness to a specific area affected for 36 of 112 (32.1%)
cases. Lameness affecting the horse in a generalized manner was reported for
27 of 112 (24.1%) cases, these conditions included non-specific arthritis,
stiffness and soreness, and exertional myopathy. Sore backs were implicated
in 8 of 112 (7.1%) of the Other lamenesses.

Horses affected by lameness--Within the study population, a significant
difference (p50.05) in the distribution of lameness cases between individual
horse characteristic categories was found for Sex (p=0.001), stallions and
geldings had a higher proportion of lameness cases than did mares; Registration
(p = 0.05), registered horses had a higher proportion of lameness cases; Activity
(p =0.001), more exercise intensive types of activity had higher proportions of
lameness cases; and Exercise (p =0.001), increasing amounts of exercise had
higher proportions of lameness cases. Figures 2.1—2.3 depict the proportion of
lameness cases within Breed, Activity, and Exercise categories, respectively.

Within the lame horse population, no significant differences (p20.05) were

 

 

49

found between the distribution of the Area Affected categories and each of the

individual horse characteristics evaluated.

16.0 —
14.0 -
12.0 —
10.0 -
8.0 -
6.0 -

4.0 -

Proportion Lame (%)

2.0 J

 

0.0 -

Quarter Saddle SB TB Mixed Other
n=1 133 n=671 n=661 n=445 n=647 n=427

Breed

Figure 2.1

The proportion (%) of incident lameness cases within Breed categories (Quarter
Horse type (Quarter), Saddle horse type (Saddle), Standardbreds (SB),
Thoroughbreds (TB), Mixed breeds (Mixed), and Other breeds (Other)) from the
population of 3,925 horses monitored (1992-1994; Michigan, USA).

49

found between the distribution of the Area Affected categories and each of the

individual horse characteristics evaluated.

16.0 —
14.0 —
12.0 -
1o.o —
8.0 -
6.0 I

4.0 -

Proportion Lame (%)

2.0 -

 

0.0 —

Quarter Saddle SB TB Mixed Other
n=1 133 n=671 n=661 n=445 n=647 n=427

Breed

Figure 2.1

The proportion (%) of incident lameness cases within Breed categories (Quarter
Horse type (Quarter), Saddle horse type (Saddle), Standardbreds (SB),
Thoroughbreds (TB), Mixed breeds (Mixed), and Other breeds (Other)) from the
population of 3,925 horses monitored (1992—1994; Michigan, USA).

50

     

 

20.0 -
18.0 -
16.0 -
g 14.0 -
I; 12.0 -
E 10.0-
_I
c 8.0 -
0
:E 6.0 -
3 4.0 -
O
E 2.0 7
0.0 -
Breed NSA Other Show Race
n=304 n=2541 n=513 n=478 n=148
Activity
Figure 2.2

The proportion (%) of incident lameness cases within Activity categories
(Breeding (Breed), No specific activity (NSA), Activities other than Showing or
Racing (Other), Showing (Show), Racing (Race)) from the population of 3,925
horses monitored on 138 equine operations (1992-1994; Michigan, USA).

 

 

51

20.0 —
18.0 —
16.0 —
14.0 -
12.0 -
10.0 —
8.0 —
6.0 -
4.0 ~
2.0 —
0.0 —

Proportion Lame (%)

 

   

None Low High
n=2917 n=539 n=528

Exercise

Figure 2.3

The proportion (%) of incident lameness cases within Exercise categories
(None, Low, and High) from the population of 3,925 horses monitored on 138
equine operations (1992-1994; Michigan, USA).

 

52
DISCUSSION

The MEMS Phase-ll equine health-monitoring study was unique in that
it was based on a population of horses within horse operations that were
randomly selected, based on region and operation size, to represent the
distribution of horses within Michigan. Data relating to lameness, collected
during the MEMS Phase II, have been summarized here to provide baseline
information about the impact of lameness on the Michigan horse population.
These data have also been used to evaluate the association between operation
management and environmental risk factors on the occurrence of lameness in
Michigan horses (Ross and Kaneene, 1996a,b; Ross et al., 1997).

Unlike other prospective studies of general horse health (Jeffcott et al.,
1983; Rossdale et al., 1985), this study was not limited to a specific breed or
horse activity. And, because this was a general health monitoring study, it was
not specifically focused on lameness. Therefore, there were some limitations
in the evaluation of lameness attributable to the study design. For example,
because the study focused on general health problems, the information
available for individual lameness cases was not as detailed as that found in
clinical trials or in lameness studies within specific breeds or activities.

In this study, the outcome of interest was a reported case of lameness.
It is important that diagnosis of the lameness could have been made by the
operation owner, manager, trainer, veterinarian, or farrier and, that some of the
conditions reported were associated with structures of locomotion, yet it was

not indicated whether or not the horse was lame in every case. Because

 

 

53

confirmation of the diagnosis could not made, diagnostic accuracy and
consistency was difficult to establish in this study. Without diagnostic
confirmation of the types of lameness reported, the actual types of lameness
reported may have been misclassified. However, 56% of the lameness cases
reported had a veterinarian involved with the diagnosis and treatment. This
should have served to minimize the potential bias related to misclassification of
the lameness cases. Also, monitoring and data collection were conducted
prospectively, which should reduce recall bias associated with lameness case
identification. For the purposes of this study, the reported, but not necessarily
confirmed, type of lameness was used to describe the types of lameness
perceived by operators to be affecting their horses.

Magnitude and severity of lameness--The Period Prevalence of lameness,
which identifies the magnitude of lameness in the population during a given
time, indicates that for every 100 horses monitored almost 27 could be
expected to be lame on any given day during the 2-year study period.
Compared to all health problems reported in the MEMS Phase-ll study, when
all types of lameness were combined, Mortality Rate was second only to
systemic problems and the Case Fatality Rate was ranked 4th after systemic
problems, miscellaneous problems, and colic (Kaneene et al., 1997b). In
contrast, the Average Annual Incidence Density was the highest for all types

of lameness combined (Kaneene et al., 1997b).

 

 

54

Previous studies have reported that lameness, followed by respiratory
conditions, were the major reasons for horses being unable to race (Jeffcott et
al., 1982; Rossdale et al., 1985). However, the rates of wastage were not
computed. One study reported that veterinary practitioners ranked colic,
followed by respiratory tract infections as the top 2 disease problems of adult
horses. However, no surgical or lameness problems were included in the
ranking (Traub-Dargatz et al., 1991). Direct comparisons between these types
of studies and the MEMS Phase-ll study are difficult because the ranking of
disease problems have been limited to a specific breed or age population or
because the rates of disease were not computed. Although lameness did not
have the highest MR or CFR compared to other health problems in the MEMS
Phase-ll study, because it was within the top 4 ranking for both, mortality
attributable to lameness may be a mechanism for substantial loss of horses.
The number 1 ranking for incidence density (AAID) amongst all types of health
problems indicates that lameness was the most commonly occurring health
problem affecting horses, which in turn may have affected the productivity and
performance of horses and may indicate an area to target with respect to
animal welfare.

Losses attributable to lameness--The duration per case and the
performance-days lost per case were used as a measure of productivity loss
attributable to lameness. When compared to all other health problems reported,
lameness was 2nd only to neurological problems for both of these measures

(Kaneene et al., 1997b). For an incident case of lameness, the average

55

duration was about 1.5 months and an average of 1 week of performance was
lost. In contrast, prevalent cases tended to include more chronic types of
conditions lasting an average of almost 5 months. Horses having an incident
case of lameness may have left the study population prior to recovery because
the condition became chronic. For these horses, the actual duration of
lameness would be underestimated. Therefore, chronic, long duration types of
lameness may need more specific methods of case evaluation.

The average performance-days lost was lower than the reported duration
of lameness. The values for performance-days lost may be low because
reporting for performance-days lost was not as consistent as anticipated. For
example, in some operations, a horse may have reduced or changed activity to
accommodate recovery but may not have lost the day altogether. Some
operators considered this a day lost, others did not. Also, the days lost
because of mortality, an unquantifiable number, were not included. Rossdale
et al. (1985) reported that 198 cases of lameness accounted for 6,649 of
114,933 (5.8%) days of cantering exercise lost for the Thoroughbred race
horses in their study. From their data, we computed an average performance-
days lost per case of 33.6 days (6,649/198). The duration of lameness in this
study (43.1 days) was comparable to this figure while performance-days lost
(8.3 days) was much lower. Therefore, duration, rather than performance-days
lost may provide a more accurate reflection of productivity lost.

Few studies have been reported dealing with the expenses associated

with the treatment of lameness cases. The expenses incurred to treat

 

56

lameness are another means of decreasing the productivity of the equine
industry (Table 2.3). In this study, it cost operators almost $60.00 on average
to treat a case of lameness. No treatment expenses were reported for 129 of
357 (36.1%) incident lameness cases which may indicate that these lameness
cases were not severe enough to require professional attention, that the
required treatment modality was already available on the operation (e.g.
hydrotherapy or rest), or that the actual expenses were not reported. Almost
40% of the cases had no associated treatment expenses which may explain
why the average treatment expense seems somewhat low.

Expenses were also incurred because of culling horses from the operation
and because of labor hours required for treatment of the case. However,
monetary values were not reliably available. Of the horses culled because of
a disease problem, one-third of the culls were attributable to lameness alone.
Furthermore, these figures may underestimate the impact of lameness culling
because they do not include horses that were culled because of poor
performance, which may have been because of an undiagnosed type of
lameness. When evaluating the impact of culling attributable to lameness, it
should be recognized that expenses attributable to replacement costs,
unrealized earnings from purse or prize money, or future sales of the animal or
its offspring should be included. With respect to expenses attributable to labor,
an average of 3.5 labor hours were required to treat a case of lameness.

Considering that lameness had the highest incidence density of all types of

57

health problems in the MEMS Phase-ll study, this may be another area of
substantial economic loss to operators.

The impact of lameness on loss of productivity in the equine industry is
multifaceted. As mentioned earlier, loss is not only attributable to mortality,
but attributable to morbidity and the decreased ability of horses to perform as
expected. It is important to note that expenses for prevention of lameness
were not included in this study. Therefore, the costs per case for treatment of
lameness underestimate the actual expenses associated with lameness
treatment and prevention on equine operations. Future studies should evaluate
how prevention and appropriate treatment of lameness, and their associated
expenses, affect the productivity levels of horses and of equine operations.

Lameness cases reported--A more detailed description of the types of
lameness affecting horses may provide insights into the impact of lameness on
the equine industry and into the development of methods of lameness
prevention. In this study, the types of lameness cases reported were diverse.
Only 17% of the lameness cases did not have a diagnosis including the area of
the body affected, compared to a previous study having 31% of the lameness
cases not diagnosed (Rossdale et al., 1985). Yet, because of differing methods
of lameness categorization, direct comparisons of our results to other studies
are difficult. However, the trends in the frequency of specific types of
lameness tended to follow results from studies conducted within the racing
industry. In this study, Hoof lameness was the most frequently reported type

of lameness, followed by lameness affecting the cannon bone region, the

 

 

58

fetlock and ankle region, and the carpus. Other studies have reported that the
most common type of leg lameness involved the cannon bone and associated
structures, followed by the fetlock region, and the carpus (Rossdale et al.,
1985; Mohammed et al., 1992). Hoof lameness was the second most common
type of lameness in previous studies (Jeffcott et al., 1982; Rossdale et al.,
1985). However, the specific hoof conditions were not described. It is
interesting that in this study, 6.4% of lamenesses were reported as hock
lameness and 7.0% as lameness associated with the stifle. In the study by
Rossdale et al. (1985) only 2% of the lamenesses were hock lamenesses and
in the study by Mohammed et al. (1992) no hock injuries were reported.
Neither study reported stifle lameness or injury. The higher proportion of hook
and stifle lamenesses in this study may be a reflection of the diversity of
activities of the horses in the study population, particularly the inclusion of
Standardbred-race horses and show horses.

In the MEMS Phase-ll study, because conditions affecting the hoof region
were the most commonly reported types of lameness, hoof-associated
lameness was grouped into one category for comparison. Hoof lameness had
the lowest AAID, MR, CFR, Lameness Cull Percentage, expenses per case, and
total dollars spent for treating lameness of the 3 lameness categories evaluated.
Farrier fees were highest for Hoof lameness as would be expected. Yet, the
overall amount appears low. It is important that only 9 lameness cases had
expenses reported for treatment by a farrier. This is because most farrier work

was reported as a preventive, and was not included as a treatment expense.

59

Hoof lameness also had the highest expense per case reported for owner
purchased drugs. This may indicate that within the Hoof lameness category,
the operator was able to treat with drugs purchased from places other than
from a veterinarian. Hoof lameness required the highest average labor hours
per case for treatment. Relatively large time requirements for treatment may
have occurred because of the relatively long duration of cases and because of
the types of treatments that may have been used, such as soaking hooves.
Overall, although hoof-associated lameness was reported relatively frequently,
when it did occur, it was relatively mild with respect to mortality and treatment
expenses.

Lameness affecting any structure of the leg, not including the hoof, was
the most common type of lameness within the 3 categories evaluated. Leg
lameness had the highest AAID and the shortest average duration reported.
Veterinary fees were the highest and owner purchased drugs the lowest
expenses per case for the Leg lameness category. This may indicate that the
conditions included in this category were relatively severe or complex, requiring
more extensive diagnostics, testing, and trial of different treatment modalities.
Even though Leg lameness occurred more frequently and had the shortest
average duration, the total expenses reported by operators for the treatment of
lameness was the highest for Leg lameness. Therefore, Leg lameness may be
a critical area to target with respect to decreasing productivity losses in the

equine industry and to developing improved methods of lameness prevention.

60

The Other lameness category included all lamenesses other than those
identified to be associated with a specific region of the leg. Lameness in this
category had the highest MR, CFR, Lameness Cull Percentage, Duration, and
expenses per case. Expenses were highest within the veterinary and owner
purchased drugs categories. Lameness in this category included chronic, long
duration, conditions and undiagnosed lamenesses. Therefore, relatively high
medication expenses may have resulted from prolonged treatment duration and
trial of different treatment modalities. Overall, it appears that although Other
types of lameness do not occur as often as Leg lameness, they are important
types of lameness to be able to prevent, because when they do occur, they are
severe with respect to mortality, they last a long time, and they are expensive
on a per case basis.

Horses affected by lameness--When compared to mares (153 lame of
2,126 mares (7.2%)), both stallions and geldings had a higher proportion of
lameness cases, 49 of 447 (11.0%), and 155 of 1,202 (12.9%), respectively.
Estberg et al. (1996) reported that males were at 2-times the risk of fatal
musculoskeletal racing injury compared to mares. In this study, 204 of 1,649
(12.4%) males (stallions and geldings combined) had a reported lameness case,
almost 2 times the proportion of lameness cases within the population of
mares. Previous studies have argued that the decreased occurrence of
lameness in fillies during their racing career is associated with the fact that

fillies are more often retired early for breeding purposes--decreasing their risk

61

of exposure to lameness associated risk factors (Jeffcott et al., 1982; Lindner
and Dingerkus, 1993). This may be the case within the equine industry overall.

Quarter Horses, Thoroughbreds, and Mixed breeds had the highest
proportion of lameness cases (Figure 2.1). Johnson et al. (1994) reported that
racing injuries occurred more frequently than training injuries in Quarter Horses
than in Thoroughbreds. This may have been associated with differences in
distance raced, method of training, or conformation. In our study, within breed
categories, horses participated in many different types of activities. Therefore,
it was difficult to use breed alone when evaluating the types of factors that
may predispose horses to lameness. It is interesting that there was a
significant increase in the proportion of lame horses in the population of horses
registered with a breed or color association. For many activities, registration
is required for participation. Therefore, lameness may occur in registered
horses more often because they tend to be more active horses.

Because horses may have participated in more than one activity during
the study period, a mutually exclusive categorization scheme was developed to
evaluate activities. These categories were developed to depict increasing
exercise intensive types of activity: Breeding, No Specific Activity, Activities
other than racing or showing (Other), Showing, and Racing. In general, the
proportion of lame horses increased across these categories (Figure 2.2).
Therefore, the specific activity in which a horse participates may be associated
with the risk of experiencing lameness. Occupational hazards were also

reported within the racing industry when it was found that there were fewer

62

catastrophic injuries per race week for quarter-mile and harness racing and
training than for Thoroughbred racing and training (Johnson et al., 1994).
Dolvik(1994) also reported that 2—year old Norwegian coldblooded trotters that
were fast trained or walked in a jog cart were at increased risk of serous
carpitis compared to 2-year olds kept in a paddock. Within showing activities,
Dyson et al. (1992) reported that hitting a fence while jumping was the cause
of 87% of horses examined for fracture of the medial aspect of the patella.

The amount of exercise also appears to be an indicator of the occurrence
of lameness. As expected, the proportion of lame horses increased with
increasing amount of exercise (Figure 2.3). An increase in the incidence of
lameness was also reported in Thoroughbred racehorses in the month of
March--directly correlated with the beginning of more-intensive race training
(Lindner and Dingerkus, 1993). Estberg et al. (1996) reported that high total
and average daily rates of exercise distance accumulation within a 2-month
period were associated with higher risks for fatal musculoskeletal injury during
racing.

In this study, no significant difference in the proportion of lameness
cases was found with respect to Age categories. Horses usually enter training
for a specific activity between the ages of 2-3 years old, so, it would be
expected that younger animals may be at more risk of the occurrence of
lameness. Younger racehorses were reported to experience the highest number
of fatal injuries (Johnson et al., 1994). And, Lindner and Dingerkus (1993)

reported that the largest proportion of racehorses experiencing training failure

 

63

attributable to lameness, infectious disease, and other causes were 2-year-olds.
In contrast, older animals may be at more risk of experiencing lameness
because of the duration of participation in exercise-related activities and the
potential for repetitive type traumatic injury.

Studies within the racing industry have reported that increasing age was
associated with an increase in racing injuries (Mohammed et al., 1991) and
severe or fatal breakdowns (Robinson et al., 1988; Estberg et al., 1996).
When age was categorized by 2, 3, and 4+ year old groups, both the 2-year-
old and 4+ year-old groups had the highest number of performance-days lost
because of lameness (Rossdale et al., 1985). In this study, when age was
categorized as 0-2 years old, 3-4 years old, 5-8 years old, and 9+ years old,
it appears that this trend also followed for the active horse categories
(Activities other than Showing or Racing (Other), Showing, or Racing) (Figure
2.4). However, interpretation of this trend for the 0-2 year old race horses is
tenuous because of the small number of horses in this category. It is
interesting that in the racing category, the proportion of lameness cases
increased in the 5-8 and 9+ year age categories, while the proportion lame
actually stayed the same or decreased in the other two activity categories.
Therefore, although there was no significant difference in lameness with
respect to age overall, the importance of age should not be underestimated
especially because of the variety of types of activities that horses were doing

within the study population and the range of ages at which horses were

 

64

    

 

30.0 —
I Racing

25.0 - IjShowing
é I Other
a, 20.0 -
E
3
c 15.0 —
.2
E 10.0 -
a.
O
h
“- 5.0 —

0.0 —

n= 3 32 62 n= 59 93 83 n= 58 133126 n= 27 214 204
- - - 8 9+
Age (years)
Figure 2.4

The proportion (%) of incident lameness cases within the Racing (Race),
Showing (Showing), and Activities other than Showing or racing (Other)
categories within Age categories (0-2 years old, 3-4 years old, 58 years old,
and 9+ years old) from the population of 3,925 horses monitored on 138
equine operations (1992-1994; Michigan, USA).

65

performing these activities. In the future, the impact of lameness on the
productivity of older horses, particularly in the racing industry, should be
investigated.

Within the lame horse population, individual horse characteristics were
evaluated with respect to the specific Area Affected. Although it did not meet
our criteria for statistical significance, the Area Affected by lameness may also
differ with respect to Age (p $0.06). As depicted in Figure 2.5, younger horses
(0-3 years old) had a higher proportion of leg lamenesses, decreasing across
age categories. In contrast, hoof and other types of lamenesses increased with
increasing age. Younger horses that are still growing may be at more risk of
growth-related disorders, such as developmental orthopedic disease and angular
limb deformities. They may also suffer from lameness caused by early training
and higher performance intensity. As horses age, their performance demands
may change and the results of long term exercise and performance may
become manifest in various arthritic conditions, chronic laminitis, or navicular
disease. In the future, the types of lameness that are occurring, with respect
to both age and activity, should be evaluated to assess the impact of lameness

on horse populations.

66

 

 

70.0—
60.0
’3
23 50.0
d)
E 40.0
" l
S 30.0 1
t
3 20.0
o
L
D- 10.0
0.0
0-3 4-7 8-12 13+
n=72 n=112 n=87 n=85
Age (years)
Figure 2.5

The proportion (%) of Leg, Hoof, and Other lamenesses (Hip/Shoulder/Back,
Generalized, and No Specific Area categories combined) cases within Age
categories (0-3 years old, 4—7 years old, 8-12 years old, 13+ years old) for
357 incident lameness cases reported from the population of 3,925 horses
monitored on 138 equine operations (1992-1994; Michigan, USA).

Chapter 3

AN OPERATION-LEVEL PROSPECTIVE STUDY OF RISK FACTORS
ASSOCIATED WITH THE INCIDENCE DENSITY OF LAMENESS IN
MICHIGAN (USA) EQUINE OPERATIONS

ABSTRACT
Objective--To evaluate the association between operation-level risk factors and
the incidence density of lameness on Michigan equine operations.
Hypotheses--An increase in the incidence density of lameness on equine
operations is associated with 1) having horses that participate in exercise-
related activities and 2) the specific types of bedding and flooring available.
Design--Prospective cohort study design.
Study population--The study population included 3,925 horses monitored for
a total of 814,753 horse-days from 138 randomly selected Michigan horse
operations.
Procedure-During two 12-month rounds of data collection, inventory, health,
activity, and economic data were collected prospectively for all horses in each
operation participating in Phase II of the Michigan Equine Monitoring System

study. A multivariable Poisson regression model was developed to evaluate the

67

68

association between equine operation-management and environmental risk
factors and the incidence density of lameness.

Results--The median incidence density of lameness was 2.8 cases per 10,000
horse-days at-risk (Minimum=0; 25th Quartile=0; 75th Quartile: 10.2;
Maximum=48.5). Management risk factors associated with the incidence
density of lameness included the total operation horse-days monitored (3rd
Quartile (Q): Relative Risk (RR) =0.46; 95% Confidence Interval (CI): 0.29-0.71
and 4th Q: RR=0.24; 95% CI: 0.16-0.37), the veterinary-related services
score (3rd Q: RR=0.61; 95% CI: 0.39-0.96 and 4th Q: RR=1.45; 95% CI:
1.01-2.08), the farrier-related services score (4th Q: RR= 1.60; 95% Cl: 1.07-
2.42), and operations having horses participating in exercise-related activities
(RR=1.71; 95% CI: 1.16-2.50). Environmental risk factors associated with
the incidence density of lameness included operations with stalls having
medium flooring (RR =0.48; 95% CI: 0.35-0.65), operations with stalls having
loose flooring (RR =2.78; 95% CI: 1.88-4.10) and operations using straw-like
materials for stall bedding (RR=2.02; 95% CI: 1.53-2.68).
Conclusions--Operations that had stalls with gravel or sand flooring and stalls
bedded with straw were 2 times more likely to have a reported lameness case,
compared to operations using other types of flooring or bedding, while there
was a 50% reduction in the risk of lameness on operations that had dirt or clay
flooring. Increasing operation size was associated with a reduced risk of
lameness, which may be attributable to the type of health management or

environment available to horses or to the types of horses that are generally kept

 

 

69

in larger operations. Operations perceiving veterinary and farrier services to be
important had relatively high rates of lameness, which may be attributable to
improved reporting or record-keeping systems on those operations. Operations
that had horses participating in exercise-related activities had an almost 2-fold
increase in the risk of having a horse become lame, suggesting that activity
may put horses at risk of lameness.

Clinical implications--Further investigation of lameness prevention should be
focused on operations with loose flooring or those using straw for bedding, on

smaller operations, and on operations with active horses.

70
INTRODUCTION

Estimates of annual losses to the United States Thoroughbred industry
due to lameness of $250 million (MacKay-Smith, 1979) and $500 million
(Leach and Crawford, 1983) have been reported. In England, losses in one
season due to keep and training fees for Thoroughbred horses that did not run
were estimated at £3.7 million, not including costs such as lost stallion fees or
mare care (Jeffcott et al., 1982). Although they are difficult to quantitate,
lameness accounts for other losses to the equine industry including decreased
performance levels, training time lost, loss of prize earnings, and decreased
price at time of sale.

Lameness (an irregularity or defect in the function of locomotion) has
been described as a symptom and manifestation of an underlying physical
lesion (isolated or complicated) which affects the locomotive apparatus
(Liautard, 1909, pp. 7-14; Stashak, 1987, pg. 100). This abnormality of
locomotion affects the ability of horses to perform. Within the equine industry
this decreased ability to perform translates into decreased productivity.

Most research on equine lameness has focused on diagnosis and
treatment of specific lameness conditions. Few population-based prospective
studies have been conducted that evaluate the risk factors predisposing horses
to lameness problems. Prospective daily monitoring of racehorses in race
training has been reported (Jeffcott et al., 1982; Rossdale et al., 1985; Kobluk
et al., 1990). Of these studies, only Kobluk et al. (1990) included an

evaluation of risk factors associated with the occurrence of lameness. Even

71

fewer studies have described lameness problems experienced by horses
performing activities other than racing (Bell and Lowe, 1986).

The activities of horses--racing or non-racing--may affect the types of
lameness reported (Stashak, 1987; Dyson et al., 1992; Dolvik, 1994).
Preexisting conditions such as stress fractures predispose racehorses to severe
musculoskeletal injuries (Stover et al., 1992). Also, environmental conditions
(such as the stall flooring and bedding) may be associated with equine
lameness as they are associated with dairy-cattle lameness (Rowlands et al.,
1983; Faye and Lescourret, 1989; Philipot et al., 1994).

The purpose of this study was to evaluate prospectively the associations
of operation-management and environmental risk factors with the incidence
density of lameness in a stratified random sample of Michigan equine
operations. The specific hypotheses tested were that an increase in the
incidence density of lameness on equine operations is associated with 1) having
horses that participate in exercise-related activities and 2) the specific types of

bedding and flooring available.

MATERIALS AND METHODS
Study population-~The Michigan Equine Monitoring System (MEMS)
project was developed jointly between the Michigan State University College
of Veterinary Medicine-Population Medicine Center, the Michigan Agricultural

Statistics Service, the Michigan Department of Agriculture, the Michigan Farm

 

72

Bureau, the Michigan United States Department of Agriculture-Animal and Plant
Health Inspection Service/Veterinary Services, and the Michigan Horse Council.

Details of the design and implementation of the MEMS project have been
published (Kaneene et al., 1995a). Briefly, the project was conducted in two
phases. Phase I, conducted in June 1991, established baseline information on
the Michigan equine population which included an equine census, a description
of the types of horses1 and their types of activities in the state, and an
economic description of Michigan equine operations. Phase II, the equine
health-monitoring study, was conducted in two rounds (Round 1: February
1992-January 1993; Round 2: May 1993-April 1994). Details of the sampling
procedures used in Phase II and the results of state-wide sampling obtained
have been published (Kaneene et al., 1995b). Briefly, each round consisted of
a subsample of operations from the Phase-l data base. Each subsample was
randomly selected using a probability-based sampling procedure which stratified
operations by MEMS region and Michigan Agricultural Statistics Service
operation-Size codes.

Study design-Details of data collection methods used for the MEMS
Phase-ll equine health-monitoring study have been published (Kaneene et al.,

1995b). Briefly, the equine health-monitoring study was designed as a

 

1 The term horse will be used to include any of the family of Equidae

including horses, asses, and zebras.

 

 

73

prospective epidemiological study. Equine operations, whose operators
consented to participate, were enrolled in the study for 12 months.
Participating operators were interviewed on a monthly basis by a state,
federal, or university veterinarian or animal technician (a MEMS data collector).
Data regarding operation management, operation environment, and other
information not expected to change on a monthly basis were collected at the
beginning (initial management surveys) and at the end of the study (close-out
survey). Equine health status and activities, and operation economic data were
expected to change on a daily basis. These types of data were recorded by
operators throughout each month of data collection. On a monthly basis, the
MEMS data collector for each operation interpreted, summarized, and recorded
these data on data-collection instruments specifically designed for data entry.
The MEMS Phase-ll database was used for the purposes of this
investigation. The horse-day, representing each day a horse was monitored
during the study period, was the unit of observation. The total number of
horse-days contributed to the study was computed for each operation.
Operation-level data characterizing potential risk factors associated with
lameness were summarized from the initial and close-out management surveys.
Specific information about the equine inventory and the lameness status of
individual horses was summarized from the monthly data-collection instruments
which included the dates of entry and exit of individual horses and the dates

that lameness cases were noted and recovered.

74

Lameness: Operation level--A horse was considered to be a lameness
case if it was reported to Show signs of abnormal locomotion in one or more
gaits. Diagnosis of the lameness may have been made by the operation owner
or manager, veterinarian, trainer, and/or farrier. Recovery from lameness (the
return of a horse to expected locomotor abilities) was also assessed by the
operation owner or manager, veterinarian, trainer, and/or farrier.

The impact of lameness in operations was measured using the incidence
density of lameness. Incidence density (ID) was computed using the following
equaflon

New Cases

ID = ,
Horse—Days At—R1 sk

 

where New Cases is the number of new cases of lameness on the operation
during the study period and Horse-Days At-Risk is determined by the difference
(Total operation horse-days - Total operation horse—days lame); Total operation
horse-days is the total horse-days monitored in the operation during the study
period and Total operation horse-days lame is the total horse-days with
lameness reported in the operation during the study period.

Horse-days at-risk of lameness were accumulated for each horse. Each
horse entering into the study population accumulated horse-days at-risk of
lameness from the recorded entry date. A horse was removed from the at-risk
population when it exited the operation or when a new, or incident, lameness
case was reported. For an individual experiencing a lameness case, after a

recovery date was recorded, it was again included in the at-risk population. lf

75

a horse experienced multiple simultaneously occurring lameness problems, each
lameness case report was considered to be a new case and added to the
numerator of the ID calculation. When this occurred, the horse-days at-risk
included only those days not reported to be lame for any reason. A horse that
entered the study with a lameness problem (prevalent case) was not considered
to be a new case and was not included in the numerator of the ID computation.
However, the total horse-days that the individual was lame, beginning on the
date of entry into the study, was included in the denominator of the ID
computation.

Risk factors investigated--Operation-management risk factors assessed
focused on the type of operation and its general equine population. The size
of the operation and the turnover of horses was described using the total
number of horses that entered the operation (NHORSES) and the total number
of horse-days contributed to the study by those horses (THDAYS), each
categorized by quartiles. The average age of horses on the operation, weighted
by the number of horse-days contributed by the individuals with an age
reported (weighted average age), was also evaluated using categorization by
quartiles (AVGAGE). The value of veterinary- and farrier-related services to
operators were assessed using a Likert format (Kelsey et al., 1986). The
scoring system ranged from 1 (not important) to 4 (extremely important) and
included 0 (not applicable). The total scores for 1 1 veterinary-related services
(VTSCORE) and for 9 farrier-related services (FTSCORE), categorized by

quartiles, were then assessed (Kelsey et al., 1986). Whether or not the

76

operator reported that at least one type of exercise-related activity was
conducted on the operation (e.g. racing, showing, race or show training,
lessons, and/or draft work) (ACTIVE) was also assessed.

Environmental risk factors assessed included the types of stall flooring
and stall bedding to which horses were exposed on the operation. The stall
flooring found in operations was categorized in relationship to its degree of
concussion or resistance during standing including hard flooring (e.g. cement)
(FHARD), medium flooring (e.g. dirt or clay) (FMED), and loose flooring (e.g.
sand or gravel) (FLOOSE). Bedding categories evaluated included the use of
straw-like materials (e.g. straw or hay) (BSTRAW), other types of bedding
materials used (e.g. sawdust or wood shavings) (BOTHER), and no bedding
used (BNONE).

Statistical analyses-Evaluation of risk factors associated with the ID of
lameness was performed by analyzing the data in a prospective cohort-study
format. The Statistical Analysis System for Personal Computers (PC-SAS) was
used to compute operation-level summary statistics and to conduct Poisson
multivariable regression analysis between the risk factors assessed and the
outcome of interest (SAS Institute Inc., 1985; SAS Institute Inc. (PROC
GENMOD), 1993).

Poisson multivariable regression was used to evaluate the association
between operation-management and environmental risk factors and the ID of
lameness. The Poisson probability distribution is given by the formula

where A is the rate of lameness determined by k/l; k is the number of events

77

Ake"

Probability of 1: events = P(X=k) = k'

 

(New Cases) and | is the accumulated length of disease-free follow-up time
(Horse-Days At-Risk) (Kleinbaum et al., 1978, pp. 497-512; Schukken et al.,
1991; Selvin, 1995, pp. 455-495). The Poisson multivariable regression

model, using the log link function (SAS Institute Inc., 1993), is given by

log(k) = log(l) + bO + b1X1 +. . .+ ann

where k is New Cases, I is Horse-Days At—Risk, logll) is the offset (a regression
variable with a constant coefficient of 1 for each observation (SAS Institute
Inc., 1993)), bO is the intercept parameter to be estimated, n is the number of
risk factors to be evaluated in the model, b1,...bIn are the parameter estimates
for each of the n risk factors, and X1,...Xn are the predictor variables for each
of the n risk factors (SAS Institute Inc., 1993).

Summary statistics were computed for each of the risk factors evaluated.
Spearman correlation coefficients (r) were computed to identify potential areas
of multicollinearity between each of the risk factors. Univariable Poisson
regression was conducted for each of the risk factors of interest to assess their
degree of association with the outcome variable.

The likelihood ratio statistic was used for model development. During
model development, it was important to be able to compare the same data set
with respect to the inclusion or exclusion of risk factors. Assessment of the

differences between operations with complete and incomplete (missing values

 

78

for one or more of the risk factors of interest) data sets was conducted using
the Wilcoxon rank-sum test (continuous) and the Mantel-Haenszel Chi-square
or 2-tailed Fisher’s-exact test (categorical) where appropriate.

Only those operations with complete data sets were used for
multivariable analysis. Rather than using a fully-saturated model containing all
risk factors assessed, a starting model containing a selected subset of risk
factors was used (Hosmer and Lemeshow, 1989). The starting model
contained operation-management and environmental risk factors having a -2
Log-Likelihood p-valueS0.05 on univariable Poisson regression. Two-factor
effect modifiers in the starting model were to include those risk factor
combinations having expected biological meaning. To avoid multicollinearity,
when the correlation between a pair of risk factors was r>0.5, one of the two
variables was selected (using biological criteria) for deletion. A backward
method of variable evaluation using the likelihood ratio statistic was conducted
to assess risk factor inclusion in or exclusion from the final model. Ultimately,
the most parsimonious model was chosen to represent the data collected.
Residual diagnostics were examined to identify potential outliers (SAS Institute
Inc., 1985; SAS Institute Inc., 1993). An assessment of the goodness-of—fit
of the final model was made by examining deviance residuals and testing them

for normality (SAS Institute Inc., 1985; SAS Institute Inc., 1993).

79
RESULTS

Study population--A total of 138 Michigan equine operations participated
in the MEMS Phase-ll equine health-monitoring study, 77 from round 1
(Response percentage: 77% (77 participated/100 contacted) and 61 from
round 2 (Response percentage: 68% (61 participated/90 contacted). The total
number of horses on 138 operations monitored in the two rounds of data
collection was 3,925 (Minimum (Min) =1; 25th Quartile (Q) =6; Median=14;
75th Q = 34; Maximum (Max) = 423) with an accumulated total operation horse-
days monitored of 814,753 (Min =116; 25th Q = 1,417; Median =2,584; 75th
Q = 7,899; Max = 58,964). The median weighted average age of horses in 136
of these operations was 8.4 years (Min=1; 25th Q=6.5; 75th Q=11.4;
Max=25.3).

Lameness: Operation level--A total of 384 cases of lameness were
reported for 298 horses in 92 operations during the study period. A
veterinarian was associated with the diagnosis in 40.4% (155/384) of all
lameness cases reported. There were a total of 365 new cases of lameness
reported for 284 horses and 19 prevalent cases of lameness reported for 18
horses. For horses with a reported new lameness case, 79.9% (227/284) had
a single case, 13.4% (38/284) had 2 cases, 5.6% (16/284) had 3 cases, 0.4%
(1/284) had 4 cases, and 0.7% (2/284) had 5 cases. The median incidence
density of lameness was 2.8 cases per 10,000 horse-days (Min = 0; 25th Q = 0;
75th Q= 10.3; Max=48.5). The median number of new lameness cases per

operation in 138 Operations was 1 case (Min=0; 25th Q=0; 75th Q=3;

80

Max=31). No new lameness cases were reported on 34.1% (47/138)
operations.

The median lameness case duration in 91 operations having at least one
new lameness case reported during the study period was 24.0 horse-days lame
(Min=1; 25th Q=13.5; 75th Q=54.0; Max:215). Sixty-one horses were
reported to have multiple cases of lameness. Simultaneously occurring
lameness cases were reported for 6.8% (26/384) of all lameness cases
reported. Overlapping days lame due to multiple simultaneous lameness case
reports accounted for 7.9% (1,455/18,430) of the total horse-days lame.
Prevalent cases of lameness accounted for 4.9% (19/384) of all lameness
cases and for 21.1% (3,896/18,430) of the total operation horse-days lame
during the study period. Ten of the 19 prevalent cases alone (52.6%)
accounted for 89.9% (3,502/3,896) of the total operation horse-days lame due
to prevalent cases. A total of 65 horses were reported to have exited the
study or were sold due to a disease problem. Thirty-one percent (20/65) of
these horses exited or were sold due to lameness problems, specifically.
Overall, 6.7% (20/298) of horses having a reported lameness case exited the
study or were sold due to lameness.

Statistical analyses: Comparison of complete and incomplete data sets--
A total of 86 out of 138 operations (62.3%) had a complete data set. There
was no significant difference (p>0.05) between those operations having
complete data sets and those having incomplete data sets with respect to the

incidence density of lameness (ID) (p =0.05), duration of lameness (p =0.05),

81

total number of horses monitored (NHORSES) (p =0.20), total horse-days
monitored (p = 0.08), weighted average age (AVGAGE) (p = 0.67), hard flooring
(FHARD) (p =0.24), medium flooring (FMED) (p = 0.56), loose flooring (FLOOSE)
(p=0.19), use of straw-like material for stall bedding (BSTRAW) (p=0.37),
other types of materials used for stall bedding (BOTHER) (p=0.10), and no
bedding used (BNONE) (p=0.99).

There were significant differences (p<0.05) between the complete and
incomplete data sets for veterinary-related services score
(VTSCORE)(p=0.001), farrier-related services score (FTSCORE) (p=0.001),
and operations with horses participating in at least one exercise-related activity
(ACTIVE) (p=0.02). In the complete data set, 45.3% (39/86) and 47.7%
(41/86) of operations had veterinary and farrier-related services scores to be
above the median value, respectively. In the incomplete data set, only 13.5%
(7/52) and 4.4% (6/52) of operations had veterinary- and farrier-related
services scores above the median value, respectively. In the complete data set,
76.7% (66/86) of operators reported having at least one exercise-related
activity conducted compared to only 41.7% (5/12) in the incomplete data set.

Statistical analysis: Model Development--Table 3.1 provides a summary
of operation-management and Table 3.2 a summary of environmental risk-factor
data compiled for the 86 operations with complete data sets. Tables 3.1 and
3.2 indicate all risk factors entering the starting model. A thorough evaluation
of potential effect modifiers was conducted and none were deemed appropriate

for entry into the starting model. The risk factors THDAYS and NHORSES had

82
a Spearman correlation coefficient of 0.89. THDAYS and NHORSES both

reflected operation size, however, THDAYS was considered to be more
representative of the population for the purposes of this study. Therefore, the
risk factor NHORSES was eliminated from the starting model.

Multivariable Poisson regression was conducted at the operation level
(Table 3.3). The goodness-of—fit of the final model was evaluated using the
likelihood ratio statistic which indicated that there was no significant difference
between the fit of the starting and final models. Residual diagnostics did not
detect any of the 86 operations to be outliers. The model deviance residuals
were not found using the Kolmogorov statistic to be distributed significantly

different from normal (p =0.17)

DISCUSSION

Study design and population--The overall response percentage of 73%
and participation rate of 79% of operations completing at least 1 1 months of
data collection in MEMS Phase-II ensured that the sample of operations was
relatively representative of the operations contacted initially (Kaneene et al.,
1995b). Reasons for non-response included not enough time to participate or
that the operation was going out of business (Kaneene et al., 1995b).

MEMS Phase-ll was designed to monitor all types of health problems
affecting horses, including lameness. The individuals monitored represented a
variety of breeds of horses and operation-management schemes and

environments within the Michigan equine industry. The data collected were not

83

Table 3.1
Description and descriptive statistics for operation-management risk factors
evaluated for 86 Michigan equine operations (1992-1994; Michigan, USA)

 

 

Risk Factor Code Description It %
NHORSESa 1 3-7 horses monitored 24 28
2 8-16 horses monitored 20 23
3 17—38 horses monitored 21 25
4 39-423 horses monitored 21 24
THDAYSb 1 486-1,539 horse-days monitored 22 26
2 1,540-3,226 horse-days monitored 21 24
3 3,227-8,387 horse-days monitored 22 26
4 8,388-42,185 horse-days monitored 21 24
AVGAGEb 1 1-6.5 years 22 26
2 6.6-8.5 years 21 24
3 8.6-11.3 years 22 26
4 11.4-25.3 years 21 24
VTSCOREb 1 0-21 total score 23 27
2 22-26 total score 24 28
3 27-31 total score 19 22
4 32-44 total score 20 23
FTSCOREb 1 2-7 total score 22 25
2 8-11 total score 23 27
3 12-15 total score 23 27
4 16-27 total score 18 21
ACTIVEb 1 Exercise-related activity/activities 66 77
0 No exercise-related activity/activities 20 23

 

a Excluded from the starting multivariable model due to the potential for
multicollinearity. b Admitted to the starting multivariable model because it
passed screening (p<0.05). detect any of the 86 operations to be outliers.
The model deviance residuals were not found using the Kolmogorov statistic to
be distributed significantly different from normal (p=0.17).

84

Table 3.2
Description and descriptive statistics for environmental risk factors evaluated
for 86 Michigan equine operations (1992-1994; Michigan, USA)

 

 

Risk Factor8 Code Description It %
FHARD 1 Hard flooring in stalls (e.g. cement) 31 36
0 No hard flooring in stalls 55 64
FMED 1 Medium flooring in stalls (e.g. dirt, clay) 70 81
0 No medium flooring in stalls 16 19
FLOOSE 1 Loose flooring in stalls (e.g. sand, 8 9
gravel)
0 No loose flooring in stalls 78 91
BSTRAW 1 Straw-like materials used for stall 39 45
bedding (e.g. straw, hay)
0 No straw-like materials used for stall 47 55
bedding
BOTHER 1 Other types of materials used for stall
bedding (e.g. sawdust, wood shavings) 53 62
0 No other types of materials used for 33 38
stall bedding
BNONE 1 No bedding used in stalls 13 15
0 No stalls without bedding 73 85

 

a Admitted to the starting multivariable model because it passed screening
(p<0.05).

85

Table 3.3

Multivariable Poisson regression model of operation-level risk factors associated
with the incidence density of lameness on 86 Michigan equine operations
(1992-1994; Michigan, USA)

 

Risk Factor b SE (b) Wald’s p RR (95% Cl)

 

Operation Management
THDAYS: lst Q3 1.00

2nd Q -0.46 0.25 0.0635 0.63 (0.39, 1.03)
3rd Q -0.78 0.23 0.0006 0.46 (0.29, 0.71)
4th Q ~1.42 0.22 0.0001 0.24 (0.16, 0.37)
VTSCOREzlst o61 1.00 -- -- -- f.
2nd Q -0.25 0.18 0.1689 0.78 (0.55, 1.11) l
3rd Q -0.49 0.23 0.0318 0.61 (0.39, 0.96)
4th Q 0.37 0.18 0.0460 1.45 (1.01, 2.08)
FTSCOREz1st Qa 1.00 -- -- --
2nd Q -0.21 0.20 0.2753 0.81 (0.55, 1.19)
3rd Q -0.31 0.22 0.1630 0.74 (0.48, 1.13)
4th Q 0.47 0.21 0.0234 1.60 (1.07, 2.42)
ACTIVE 0.53 0.19 0.0061 1.71 (1.16, 2.50)
Operation Environment
FMED -0.74 0.16 0.0001 0.48 (0.35, 0.65)
FLOOSE 1.02 0.20 0.0001 2.78 (1.89, 4.10)
BSTRAW 0.70 0.14 0.0001 2.02 (1.53, 2.68)
MODEL Deviance df LRSb (S-F) df° pLd
Starting 259.17 19 -- —- --
Final 268.18 13 9.01 6 0.81

 

3 Categories defined by quartiles (Q). b Likelihood Ratio Statistic: Deviance
(Final model) - Deviance (Starting model). ° Degrees of freedom difference
between starting (S) and final (F) models. d p-value for Likelihood ratio Chi-
square statistic.

 

 

 

 

86

limited to a specific type of equine activity (such as racing) or to a specific type
of environment (such as a race track). Because this was a general health
monitoring study, data collection did not focus on lameness only. Therefore,
all potential risk factors for lameness were not available for evaluation. Also,
because the study population was not limited to specific equine breeds,
activities, or environments, variation in the types of risk factors to which horses
were exposed may have been greater than presented in previous studies
(Jeffcott et al., 1982; Rossdale et al., 1985; Kobluk et al., 1990).

Lameness: Operation level-~For the purposes of this study, prospective
identification of lameness cases was important in reducing recall bias that may
occur over a one-year study period. The definition of lameness, its degree of
severity and time to recovery, may have varied between operations depending
on how the lameness affected the expected level of equine productivity.
However, a veterinarian was involved in at least 40% of the lameness cases
diagnosed and reported during the study period minimizing the potential for lack
of consistency in lameness definition and diagnosis.

Because we considered lameness to be a rare event, the Poisson
regression model was chosen for data analysis. It was difficult to assess the
ID of lameness as a general disease category because horses may have been
at risk for several different types of lameness simultaneously. An individual
may have experienced a new case of lameness while still recovering from a
previous lameness. In this case, the total horse-days at-risk of lameness

included only those days with no reported lameness. Therefore, in operations

87

reporting horses with multiple simultaneous cases of lameness, the ID may
have been artificially inflated. However, an overlap of horse-days lame
occurred for only 7% of all reported cases and for only 8% of the total
operation horse-days lame.

Assessment of the ID of lameness was also affected by prevalent
lameness cases. These individuals did not contribute a new case of lameness,
but they contributed to approximately 20% of the total operation horse-days
lame. These individuals would tend to decrease the ID of lameness in
operations. Horses entering the study with chronic lameness conditions
continuing throughout the study period were the primary contributors to this
relatively large number of horse-days lame. Further investigation into the
impact of chronic lamenesses on the ID of lameness in equine operations should
be addressed.

Culling may affect the ID of lameness in operations, especially if horses
leave the operation before recovery or if those experiencing lameness are
predisposed to subsequent lameness problems. Culling on equine operations
is difficult to monitor due to the various types of operation management
employed throughout the industry. For example, individuals may be sold but
not leave the operation. Also, a horse may be removed from the training
population within an operation after becoming lame, yet remain on the
operation. Only 7% of the horses with a reported lameness case were noted
to have been sold or to have exited an operation due to a lameness problem.

Further investigation into the types of management strategies utilized on

 

88

individual operations will have to be addressed to more accurately assess the
impact of culling on the ID of lameness in equine operations.

Statistical analyses--To streamline data collection between rounds 1 and
2, minor changes were made in the data-collection instruments. Because of
this, the availability of some types of operation-level data focusing specifically
on lameness varied between rounds. Because the likelihood ratio statistic was
to be used for statistical analysis, it was important to have a complete data set
for comparison of risk factors. Only 62% of the operations monitored had
complete data sets for the operation-level risk factors of interest in this
investigation. However, comparison of the complete and incomplete data sets
with respect to these risk factors showed that only the veterinary-related
services score (VTSCORE), the farrier-related services score (FTSCORE), and
whether or not operations conducted exercise-related activities (ACTIVE) were
significantly different between the two data sets.

When the comparison of veterinary- and farrier-related services scores
between the complete and incomplete data sets was conducted, a significant
difference was found for each risk factor. Further investigation revealed that
both of these risk factors had a relatively small number of operations with
scores above the median value in the incomplete data set. This may suggest
that operations in the incomplete data set do not value these types of services
as highly as operations having a complete data set. It is interesting that when
comparison of the two data sets was conducted, with veterinary- and farrier-

related services scores coded as continuous variables, no significant difference

 

89

in their distributions was found (p = 0.82 and p = 0.14, respectively). This may
also suggest that sample size, due to categorization of the risk factors by
quartiles, may be affecting the results. Comparison of the complete and
incomplete data sets with respect to whether or not exercise-related activities
were conducted on the operation suffered due to a small sample size availability
in the incomplete data set so interpretation of this difference would be tenuous
at best.

Because there were no differences between the ID of lameness reported,
the duration of lameness, or for most of the risk factors in the complete and
incomplete data sets, minimal bias due to the lack of a complete data set
probably exists. This indicates that the complete data set should still be
relatively representative of the sample population with respect to the operation-
level risk factors of interest.

The operations participating in MEMS Phase-ll conducted a wide variety
of equine activities. Often, within operations, several types of activities were
being conducted. For example, 59% (51/86) of the operations reported having
horses participating in showing-related activities, 17% (15/86) participating in
racing-related activities, 54% (46/86) in breeding-related activities, and 46%
(40/86) participating in other types of activities. Therefore, it was difficult to
categorize operations into mutually exclusive activity groups. Whether or not
an operation reported having horses participating in at least one exercise-related
activity was associated with a 53% (95% CI: 1.16-2.50) increase in the risk

of lameness. Based on previously reported studies of equine lameness, it was

 

90

expected that participation in exercise-related activities would be associated
with an increase in the occurrence of lameness (Jeffcott et al., 1982; Rossdale
et al., 1985; Stover et al., 1992; Dolvik, 1994). Future studies will
investigate the association between specific types of activities and the risk of
specific types of lameness on an individual-animal level.

In general, increasing total horse-days monitored in an operation was
protective. When compared to operations having the total horse-days
monitored in the Ist quartile, Operations having the total horse-days monitored
in the 3rd and 4th quartiles had significant RR’S of 0.46 (95% CI: 0.29-0.71)
and 0.24 (95% CI: 0.16-0.37), respectively. Rowlands et al. (1983) also
reported a negative relationship between herd size and the ID of lameness in
dairy cattle. In contrast, Faye and Lescourret (1989) reported a positive
relationship between herd size and the incidence of lameness in dairy cattle.
Larger equine operations may include a relatively large number of inactive
individuals such as broodmares. Sixty percent (28/47) of operations reporting
breeding activities had a total horse-days monitored greater than the median
total horse-days compared to only 39% (15/39) not reporting breeding
activities (p=0.05). It would be expected that horses involved in breeding
would have a lower number of exercise-related lameness cases and that subtle
lamenesses in non-working horses may not be diagnosed. Also, the decreased
risk of lameness on larger operations may have been associated with the use

of more preventive measures to avoid new cases of lameness. More cases of

91

lameness may have been treated without veterinary assistance, and thus may
not have been reported.

If the importance of veterinary-related services was to suggest a more
intensive level of health care for horses on the operation, it would be expected
that as the veterinary-related services score increased the risk of lameness in
operations would decrease. When compared to operations with a veterinary-
related services score in the 1st quartile, operations having a score in the 2nd
and 3rd quartiles were negatively associated with the risk of lameness,
although only those with a score in the 3rd quartile had a significant RR =0.61
(95% CI: 039-096). In contrast, when the score was in the 4th quartile, the
risk of lameness increased by 45% (95% CI: 1.07-2.42). Overall, as the
veterinary-related services score increased the association with the ID of
lameness tended to be less protective. The type and amount of activity to
which horses are exposed may influence how operators perceive the
importance of veterinary-related services. Therefore, lameness detection and
reporting may affect the association between the risk of lameness and the
veterinary-related services score. Although there was no significant difference
in the distribution between operations reporting training-related activities or not
and the veterinary-related services score (p =0.09), in those operations
reporting training activities, 51 % (26/51) had a veterinary-related services score
above the median value compared to only 37% (13/35) of those that did not
report training activities. Operations that have horses participating in training

activities may be more apt to diagnose a lameness case and to be more

92

knowledgeable of the importance of veterinary care to their operation.
Therefore, the risk of lameness would be increased with increasing veterinary-
related services score.

The farrier-related services score was expected to follow a similar trend
in risk of lameness as the veterinary-related services score; as the score
increased, it was expected that the risk of lameness would be decreased.
However, as with the veterinary-related services score, an increase the farrier-
related services score was associated with an increased risk of lameness.
Operations with a farrier-related services scores in the 4th quartile were
associated with a 60% (95% Cl:1.07-2.42) increase in the risk of lameness.
In dairy cattle, a positive association between regular hoof trimming practices
and the total frequency of hoof diseases was also reported (Faye and
Lescourret, 1989). As with veterinary-related services, the activities of horses
may affect the operator’s perception of the importance of farrier-related
services. When evaluating operations reporting training activities or not, there
was a significant difference in the distribution of the farrier-related services
score (p =0.002). In particular, in operations reporting training activities, 61%
(31/51) had a farrier-related services score above the median value compared
to only 28% (10/35) of those that did not report training activities. Again,
operations that have horses participating in training activities may be more apt
to diagnose a lameness case and to be more knowledgeable of the importance
of veterinary care to their operation. This may contribute to the increased risk

of lameness associated with an increasing farrier-related services score.

93

Lameness was increased with increasing age in dairy cattle (Rowlands
et al., 1985). However, for specific types of lameness increased age was
associated with both increases (white line abscess, sole ulcers) and decreases
(foul-in-the-foot) in specific types of lameness reported. This risk factor did not
enter the final model. Equine age may be more important with respect to the
specific types of lameness occurring in operations and the duration that
lameness cases last. Therefore, analysis at the individual-animal level will
evaluate this risk factor in more detail.

The type of flooring and bedding to which horses are exposed were
associated with the occurrence of lameness on equine operations. It was
difficult, however, to evaluate flooring and bedding effects because some
operations had several types of flooring, several types of bedding used, and
each in differing proportions. The most common type of flooring found in
operations in this study was medium flooring (81% (70/86)), followed by hard
flooring (36% (31/86)), and loose flooring (9% (8/86). The most common type
of bedding used in operations in this study was other types of bedding
materials (62% (53/86)), followed by straw-like bedding materials (45%
(39/86)), and no bedding used (15% (13/86)).

Operations with stalls having medium flooring were associated with a
decreased risk of lameness (RR=0.48; 95% CI: 0.35-0.65). This type of
flooring offers both reduced concussion, compared to hard flooring, while
offering adequate drainage in stalls. In contrast, operations with stalls having

loose flooring were associated with an almost 3-fold increase (95% Cl: 1.89-

94

4.10) in the risk of lameness in operations. Loose flooring was considered to
have reduced concussion or resistance to stabled horses. However, there may
be a tendency for this type of flooring to Shift under pressure causing horses
to slip. This, in turn, may have increased the potential for individuals to take
a misstep and injure themselves. Loose flooring may also be associated with
lameness conditions related to moisture conditions or bruising of the hoof
surfaces. Only 8 operations out of 86 (9%) actually reported having loose
flooring in stalls and 4 of these 8 operations were ranked in the top 15 highest
ID values. These four operations were also reported to be active operations.
Even though cement flooring has been reported to be associated with lameness
in dairy cattle (Rowlands et al., 1983; Faye and Lescourret, 1989), the
existence of stalls with hard flooring on equine operations did not enter the final
model.

The use of straw-like materials for bedding was associated with a 2-fold
increase (95% CI: 1.53-2.68) in the risk of lameness. In dairy cattle, decreased
thickness of straw bedding has been reported to be associated with an
increased occurrence of lameness (Faye and Lescourret, 1989; Philipot et al.,
1994). Therefore, the increase in risk may be associated with the ability to
clean and bed stalls with an adequate amount of Straw.

Thirty-two out of the 40 operations (80%) reporting the use of straw-like
materials and 87% (47/54) of operations reporting the use of other types of
materials for bedding were reported to be active. However, only 50% (7/14)

of the operations having stalls with no bedding were reported to be active.

95

Specifically, 80% (12/15) of operations with horses participating in racing-
related activities used straw-like materials for bedding to some extent, while
only 40% (6/15) used other types of materials for bedding. In contrast, only
37% (19/51) of operations with horses participating in showing-related
activities used straw-like materials for bedding to some extent, while 80%
(41/51) used other bedding materials. Therefore, future studies should
investigate the specific types of management associated with the types of
activities in which horses participate to evaluate how the specific activity,
environment, or both affect the occurrence of lameness.

The type of bedding used in stalls may be selected with consideration to
the type of flooring available, the methods available to remove manure and
soiled bedding, the expense, and the convenience of storage and use. For
example, straw-like materials were used for bedding on 49% (21/43) of
operations with the total horse-days monitored greater than the median value
compared to 70% (30/43) of those operations using other types of materials
for bedding and 8% (7/43) of those using no bedding. In future studies, the
methods and frequency of stall sanitation should also be evaluated as this is

associated with increased lameness in dairy cattle (Philipot et al., 1994).

 

Chapter 4

AN INDIVIDUAL-ANIMAL-LEVEL PROSPECTIVE STUDY OF RISK
FACTORS ASSOCIATED WITH THE OCCURRENCE OF LAMENESS
IN THE MICHIGAN (USA) EQUINE POPULATION

ABSTRACT
Objective--To evaluate the association between individual-animal-level risk
factors and the occurrence of lameness in Michigan horses.
Hypotheses--The occurrence of lameness in horses is associated with 1)
participation in relatively stressful types of activities and 2) increasing amounts
of exercise.
Design-Prospective cohort study design.
Study population-~The study population included 3,925 horses monitored for
a total of 814,753 horse-days from 138 randomly selected Michigan horse
operations.
Procedure-During two 12-month rounds of data collection, inventory, health,
activity, and economic data were collected prospectively for all horses in each
operation participating in Phase II of the Michigan Equine Monitoring System

study. A multivariable logistic-binomial regression model for distinguishable

96

 

97

data was developed to evaluate risk factors associated with the occurrence of
lameness at the individual-animal level.

Results--New cases of lameness were reported in 7.2% (284/3,925) of the
horses monitored during the 2-year study period. Horses on larger operations
were associated with a decreased risk of experiencing lameness (2nd Quartile
(Q): Relative Risk (RR) =0.42; 95% Confidence Interval (CI): 0.25-0.72, 3rd
Q: RR=0.58; 95% CI: 0.35-0.95, and 4th Q: RR=0.44; 95% Cl: 0.19-
1.02). Horses participating in racing were at increased risk of experiencing
lameness (RR= 1.75; 95% CI: 1.03-2.99). Horses participating in showing
also tended to be at increased risk of experiencing lameness (RR = 1.44; 95%
CI: 0.95-2.20). Increasing exercise level, or the number of days exercised per
days available to exercise, was also associated with an increase in the risk of
experiencing lameness (Low: RR=2.32; 95% CI: 1.54-3.51 and High
exercise: RR=2.48; 95% CI: 1.58-3.90).

Conclusions--At the operation-level, increasing operation size was associated
with a reduced risk of lameness. This finding may be attributable to the type
of health management or environment available to horses or to the types of
activities to which horses are exposed. At the individual-animal-level, activity
was associated with an increased risk of lameness. In particular, compared to
all other horses, race horses and show horses were 70% and 40% more likely
to experience lameness, respectively. Furthermore, horses that were reported

to have exercised during the study period had at least a 2-fold increase in the

98

risk of experiencing lameness. These findings suggest that the risk of lameness
is associated with the occupation of the horse.

Clinical implications--Further investigation of lameness prevention strategies
should be focused on horses housed on smaller operations and on active

horses.

99
INTRODUCTION

Lameness had the highest incidence density of all health problems
evaluated during a state-wide study of horses‘ in Michigan (Kaneene et al.,
1995b). Two other studies have reported lameness to be the leading cause of
veterinary wastage in Thoroughbred horses in Great Britain (Jeffcott et al.,
1982; Rossdale et al., 1985). The occurrence of lameness in horses translates
into decreased productivity for equine operations and the equine industry
because individuals are not available to participate at all or participate at lower-
than—expected levels in the activities for which they are being maintained.

Descriptions of the types of horses experiencing specific types of
lameness have been reported. Many studies are retrospective hospital-based
studies dealing with the treatment of lameness and treatment efficacy
(Mcllwraith et al., 1991; Dyson et al., 1992; Schneider et al., 1992; Laws
et al., 1993; Lillich et al., 1995). Population-based studies of lameness have
been limited largely to a specified population including a single breed (either
Standardbred or Thoroughbred), a single occupation (racing), and a single type
of environment (the racetrack). These studies often use racetrack records or
injury reports, including both retrospective (Jeffcott et al., 1982; Hill et al.,
1986) and prospective (Rossdale et al., 1985; Stover et al., 1992; Estberg et
al, 1993; Lindner and Dingerkus et al., 1993; Wilson et al., 1993; Johnson

et al., 1994; Peloso et al., 1994) methods of data collection. Prospective daily

 

1 The term horse will be used to include any of the family of Equidae

including horses, asses, and zebras.

 

100

monitoring of horses was used to evaluate the association between exercise
level and problem rate of Thoroughbred horses (Kobluk et al., 1990). Few
studies have described lameness problems experienced by horses performing
activities other than racing (Bell and Lowe, 1986).

These types of descriptive studies have shown that the occurrence and
type of lameness in individual horses may be affected by both extrinsic and
intrinsic risk factors. Extrinsic risk factors investigated have included those risk
factors found at the operation- or racetrack-level (such as racetrack design and
racetrack surface), and those found at the individual-animal level (such as the
amount of exercise or the amount of weight carried during a race). Intrinsic risk
factors investigated have included those factors related to the characteristics
of the individual horse such as its age, sex, breed, conformation, and type of
injury, among others. For the most part, these studies have provided
information essential for use in the determination of the types of risk factors
that may contribute to the occurrence of lameness in horses.

However, the strength of the association between these types of risk
factors and the occurrence of lameness may also be evaluated by conducting
analyses which include the risk factors of interest while controlling for
potentially—confounding factors. Few studies have been conducted to evaluate
the association between risk factors and the occurrence of lameness using
multivariable analytical techniques. Mohammed et al. (1991) conducted a
retrospective case-control study using multivariable logistic regression for the

evaluation of intrinsic and extrinsic risk factors associated with injuries in

101

Thoroughbred horses. Multivariable logistic regression was also used in a
retrospective study to identify the risk of severe (compared to less-severe)
injuries in Thoroughbreds (Mohammed et al., 1992). These study populations
were each limited to Thoroughbred racehorses racing at a specified group of
racetracks in the state of New York (Mohammed et al., 1991; Mohammed et
aL,1992L

Throughout the equine industry, evaluation of risk factors associated
with the occurrence of lameness in horses can be difficult due to the diversity
in types of horses and equine operations. Differences in operation management
and operation environment vary between operations. Differences in the breeds
of horses and their specific occupations vary not only between operations, but
within operations. To evaluate equine health problems (including lameness) on
an industry-wide basis, prospective daily monitoring of horses was conducted
in a stratified random sample of Michigan equine operations (Kaneene et al.,
1995a). Investigation of the association between risk factors and the
occurrence of lameness at an operation level using multivariable analytical
techniques has been reported previously (Ross and Kaneene, 1995). However,
an analysis limited to the operation level may have minimized the importance
of individual-animal-level risk factors due to the diversity of horses within
operations.

Evaluation of risk factors associated not only with the type of operation,
but with the type of horse, the occupation of the horse, and its exercise or

performance-related activities may provide more specific information about the

102

occurrence of equine lameness and its prevention. The purpose of this study
was to evaluate prospectively the associations of individual-animal-Ievel risk
factors with the occurrence of lameness in a stratified random sample of
Michigan equine operations. The specific hypotheses tested were that the
occurrence of lameness in horses is associated with 1) participation in relatively

stressful types of activities and 2) increasing amounts of exercise.

MATERIALS AND METHODS

Study population--The Michigan Equine Monitoring System (MEMS)
project was developed jointly between the Michigan State University College
of Veterinary Medicine-Population Medicine Center, the Michigan Agricultural
Statistics Service, the Michigan Department of Agriculture, the Michigan Farm
Bureau, the United States Department of Agriculture-Animal and Plant Health
Inspection Service/Veterinary Services, and the Michigan Horse Council.

Details of the design and implementation of the MEMS project have been
published (Kaneene et al., 1995a). Briefly, the project was conducted in two
phases. Phase I, conducted in June 1991, established baseline information on
the Michigan equine population which included an equine census, a description
of the types of horses and equine activities in the state, and an economic
description of Michigan equine operations (Kaneene et al., 1995a). Phase II,
the equine health-monitoringstudy, was conducted in two rounds (Round 1:
February 1992-January 1993; Round 2: May 1993-April 1994). Details of the

sampling procedures used in Phase II and the results of state-wide sampling

103

obtained have been published (Kaneene et al., 1995b). Briefly, each round
consisted of a subsample of operations from the Phase-l data base. Each
subsample was randomly selected using a probability-based sampling procedure
which stratified operations by MEMS region and Michigan Agricultural Statistics
Service operation-size codes.

Study design-Details of data-collection methods used for the MEMS
Phase-ll equine health-monitoring study have been published (Kaneene et al.,
1995b). Briefly, the equine health-monitoring study was designed as a
prospective epidemiological study. Equine operations, whose operators
consented to participate, were enrolled in the study for 12 months.

Participating operators were interviewed on a monthly basis by a state,
federal, or university veterinarian or animal technician (a MEMS data collector).
Data regarding operation management, operation environment, and other
information not expected to change on a monthly basis were collected at the
beginning (initial management surveys) and at the end of the study (close—out
survey). Equine health status and activities, and operation economic data were
expected to change on a daily basis. These types of data were recorded by
operators throughout each month of data collection. On a monthly basis, the
MEMS data collector for each operation interpreted, summarized, and recorded
these data on data-collection instruments specifically designed for data entry.

The MEMS Phase-ll data base was used for the purposes of this
investigation. The horse-day, representing each day an horse was monitored

during the study period, was the unit of observation. The total number of

104

horse-days monitored for an individual horse was the total number of days
monitored between the date of entry into the study and the date of exit. When
a horse left the operation during the study and then returned, the days off of
the operation were not included in the total horse-days monitored. Operation-
level data characterizing potential risk factors associated with lameness were
summarized from the initial and close-out management surveys. Specific
information about the equine inventory and the lameness status of horses was
summarized from the monthly data-collection instruments which included the
dates of entry and exit of individual horses and the dates that lameness cases
were noted and recovered.

Lameness: Individual-animal level--A horse was considered to be a
lameness case if it was reported to show signs of abnormal locomotion in one
or more gaits. Diagnosis of the lameness may have been made by the
operation owner or manager, veterinarian, trainer, or farrier. Recovery from
lameness (the return of an horse to expected locomotor abilities) was also
assessed by the operation owner or manager, veterinarian, trainer, and/or
farrier.

For the purposes of this analysis, any horse with one or more reported
episodes of lameness during the study period was considered to be a case.
Horses that were lame at the beginning of the study or those that entered the
study with a lameness problem were not considered eligible to be a case until

after a recovery date for the initial lameness was reported.

105

Risk factors investigated--Operation and individual-animal-level risk
factors were examined to assess their association with the occurrence of
lameness in Michigan horses. The size of the operation and the turnover of
horses was described using the average daily operation horse-days
(OPERATION SIZE). The operation size, or average number of horses on an

operation per day, was calculated using the following equation

Operation Size = Operation Horse-Days / Study—Days

where

12
Operation Horse-Days = Z Horse—Daysim
1
and

P
Study-Days = E Calendar-Days,"
1

and where n is the number of months the operation participated in monthly
health monitoring, i is the individual operation, m is the month of data
collection, and p is the number of monitoring months in the respective round
of study. Operation size was then categorized by quartiles for analysis.
Whether or not the operator reported that at least one type of exercise-related
activity was conducted on the operation (e.g. racing, showing, race or show
training, lessons, and/or draft work) (ACTIVE) was also assessed.
lndividual-animal-level risk factors focused on the signalment of horses

and the types of activities in which they participated. Signalment information

106

evaluated included the age (categorized by quartiles) (AGE), sex (SEX), and
breed group (BREED) of the individual. The type of housing while on the
operation (HOUSING) was also evaluated. Whether or not an horse was
reported to participate specific types of activities (e.g. racing (RACE), showing
(SHOW), or other (OTHER) activities) was also assessed.

Exercise level (EXERCISE), or amount of exercise or performance to
which an horse was exposed during the study period, was measured using the

following equation

Exercise = Total Work—Days / (Total Horse-Days - Days Lost)

where Total Work—Days is the total number of days the horse was reported to
have been exercised and or to have performed, the Total Horse-Days is the
total horse-days that the individual was monitored during the study period, and
the Days Lost is the total number of exercise or performance days the individual
lost due to lameness during the study period. Evaluation of the number of trips
a horse took off the operation (TRIPS) and the total number of days spent off
the operation (DAYSOFF) during the study period were also evaluated. Each
of these three risk factors were grouped into 3 categories: None (horses having
a value of zero), Low (a value at or below the median score for all horses
having a value greater than zero), and High (a value above the median score for
all horses having a value greater than zero).

Statistical analyses--Evaluation of risk factors was performed by

analyzing the data in a prospective cohort-study format. The Statistical

107

Analysis System for Personal Computers (PC-SAS) was used to compute
operation and individual-animal-level summary statistics (Statistical Analysis
Systems (SAS) Institute Inc., 1985). The Epidemiological GRaphics,
Estimation, and Testing package (EGRET) was used to conduct univariable and
multivariable logistic-binomial regression for distinguishable data (Statistics and
Epidemiology Research Corporation (SERC), 1991).

The risk of lameness was evaluated using logistic-binomial regression for
distinguishable data (SERC, 1991). The dependent variable (lameness) was
coded as a 1 if a horse had one or more reported casels) of lameness during the
study period and a 0 if it had no reported case of lameness. Because sampling
was conducted at the operation level, a random-effects term was included
during modelling to account for extra-binomial variation attributable to lack of
independence between individual horses within operations (SERC, 1991; Curtis
et al., 1993).

Summary statistics were computed for each of the risk factors of interest
(SAS Institute Inc., 1985). Spearman correlation coefficients (r) were
computed to identify potential areas of multicollinearity between each of the
risk factors (SAS Institute Inc., 1985). Univariable logistic-binomial regression
for distinguishable data was conducted for each of the risk factors to assess
their degree of association with the outcome variable (SERC,1991).

The likelihood ratio statistic was used for model development. Therefore,
it was important to compare the same data set with respect to the inclusion or

exclusion of risk factors. Assessment of the differences between individuals

108

with complete and incomplete (missing values for one or more of the risk
factors of interest) data sets was conducted using the Wilcoxon rank-sum test
(continuous risk factors) or the Mantel-Haenszel Chi-square or 2-tailed Fisher’s-
exact test (categorical risk factors) where appropriate. A post-hoc analysis of
the complete and incomplete data sets was conducted by eliminating
operations having between $3 and 2100 average horses monitored per day.
Comparison of these data sets was conducted using the Wilcoxon rank-sum
test (continuous risk factors) or the Mantel-Haenszel Chi-square or 2—tailed
Fisher’s-exact test (categorical risk factors) where appropriate.

Only those individuals having a complete data set were used for
multivariable analysis. Rather than using a fully-saturated model containing all
risk factors assessed, a starting model containing a selected subset of risk
factors was utilized (Hosmer and Lemeshow, 1989). The starting model
contained operation- and individual-animal-level risk factors having risk ratios
(RR) with a p-value $0.50 on univariable logistic-binomial regression. Two-
factor effect modifiers in the starting model were to include those risk factor
combinations having expected biological meaning. A backward method of
variable evaluation using the likelihood ratio statistic was conducted to assess
risk factor inclusion in or exclusion from the final model. The three activity risk
factors (RACE, SHOW, and OTHER) were forced into the final model to provide
an indication of the relative importance of these types of risk factors with
respect to experiencing lameness. Age and sex were also forced into the final

model to account for potential confounding. The goodness-of—fit of the final

109

model was evaluated by calculating the likelihood ratio statistic between the
starting and final models and comparing it to the chi-square distribution (SERC,
1990; Selvin, 1991). Ultimately, the most parsimonious model, maintaining
the three activity risk factors, and age and sex, was chosen to represent the

data collected.

RESULTS

Study population-~A total of 138 Michigan equine operations participated
in the MEMS Phase-ll equine health-monitoring study, 77 from round 1
(Response percentage: 77% (77 participated/100 contacted)) and 61 from
round 2 (Response percentage: 68% (61 participated/90 contacted)). The
total number of horses on 138 operations monitored in the two rounds of data
collection was 3,925 (Minimum (Min) =1; 25th Quartile (Q) =6; Median=14;
75th Q = 34; Maximum (Max) = 423) with an accumulated total operation horse-
days monitored of 814,753 (Min =116; 25th Q = 1,417; Median =2,584; 75th
Q = 7,899; Max = 58,964). The median value for the average number of horses
monitored per operation was 7.04 (Min =0.32; 25th Q =3.87; 75th O: 21.64;
Max=161.10). The median number of horse-days monitored per horse was
214 (Min=1; 25th Q=59; 75th Q=365; Max:366).

Lameness: Individual-animal level--A total of 384 cases of lameness
were reported for 298 horses in 92 operations during the study period. A
veterinarian was associated with the diagnosis in 40.4% (155/384) of all

lameness cases reported. There were a total of 365 new cases of lameness

 

110

reported for 284 horses. For horses with a reported new lameness case,
79.9% (227/284) had a single case, 13.4% (38/284) had 2 cases, 5.6%
(16/284) had 3 cases, 0.4% (1/284) had 4 cases, and 0.7% (2/284) had 5
cases. The median number of new lameness cases per operation in 138
operations was 1 case (Min=0; 25th Q=0; 75th Q=3; Max=31). No new
lameness cases were reported on 34.1% (47/138) operations.

Statistical analyses: Comparison of complete and incomplete data sets--
A total of 2,330 out of 3,925 horses monitored (59.4%) had a complete data
set with respect to the risk factors of interest, representing 97 out of 138
equine operations (70.3%). Significant differences (p<0.05) between those
horses having complete data sets and those having incomplete data sets were
found with respect to the outcome variable, lameness, and all of the risk
factors of interest.

After eliminating small (53 horses monitored) and large (2100 horses
monitored) operations from the complete and incomplete data sets, no
significant differences were found between the two data sets with respect to
the operation size (OPERATION SIZE) (p=0.07), whether or not an horse
participated in showing activities (SHOW) (p=0.08), sex (SEX) lp=0.57),
breed group (BREED) (p=0.16), the number of trips a horse took off of the
operation (TRIPS) (p=0.12), and the number of days a horse was off of the
operation (DAYSOFF) lp=0.51).

Statistical analyses: Model development--Tables 4.1, 4.2, and 4.3

provide summaries of operation- and individual-animaI-level risk factor data

111

compiled for the 2,330 horses with complete data sets. These tables also
indicate which risk factors entered the starting model and which risk factors
were maintained in the final model on a priori grounds. A thorough evaluation
of potential effect modifiers was conducted and none were deemed appropriate
for entry into the starting model. The correlation between the number of trips
off the operation (TRIPS) and the number of days off the operation (DAYSOFF)
during the study period was r=0.99. Therefore, DAYSOFF was eliminated
from consideration for entry into the starting model due to potential redundancy
of information and because exposure to risk factors off the operation were not
monitored.

Table 4.1

Description and descriptive statistics for operation-level risk factors evaluated

for 2,330 horses in 97 Michigan equine operations (1992-1994; Michigan,
USA).

 

 

Risk Factor8 Code Description n %
OPERATION SIZE 1 2.2-16.6 AHPDb 570 24.5
2 16.7-31.8 AHPD 566 24.3
3 31.9-47.9 AHPD 500 21.4
4 480-1156 AHPD 694 29.8
ACTIVE 1 Exercise-related
activities 1954 83.9
0 No exercise-related
activities 376 16.1

 

a Admitted to the starting multivariable model because it passed screening
(p<0.50). b Average number of horses on an operation per day.

112

Table 4.2
Description and descriptive statistics for individual-animal-level signalment and

housing risk factors evaluated for 2,330 horses in 97 Michigan equine
operations (1992-1994; Michigan, USA).

 

 

Risk Factor8 Code Description n %
AGEb 1 0-4 years 745 32.0
2 5-7 years 468 20.1
3 8-12 years 549 23.5
4 13-41 years 568 24.4
SEXb 1 Mare 1239 53.2
2 Stallion 289 12.4
3 Gelding 802 34.4
BREED 1 Quarter Horse typesc 749 32.1
2 Saddle typesd 407 17.5
3 Standardbred 256 11.0
4 Thoroughbred 320 13.7
5 Mixed3 456 19.6
6 Otherf 142 6.1
HOUSING 1 Indoors only 971 41.7
2 Both indoors and outdoors 970 41.6
3 Outdoors only 389 16.7

 

a Admitted to the starting multivariable model because it passed screening
(p<0.50). b Maintained in the final model on a priori grounds. ° e.g. Quarter
Horse, Paint, Appaloosa. d e.g. Arabian, Morgan, Saddlebred. ° Half-arabian,
Thorcheron. f Grade, Draft, Pony.

Table 4.3

113

Description and descriptive statistics for individual-animaI-level activity risk
factors evaluated for 2,330 horses in 97 Michigan equine operations (1992-
1994; Michigan, USA).

 

 

Risk Factor Code Description n %
RACE""ID 1 Flat or harness racing 131 5.6
0 No flat or harness racing 2199 94.4
SHOW‘"b 1 showing-related activities 342 14.7
0 No showing-related activities 1988 85.3
OTHER‘"b 1 Driving or draft-related activities 40 1.7
0 No driving or draft-related activities 2290 98.3
EXERCISE3 1 None: No exercise-daysd 1552 66.6
2 Low: >0 and $0.16 exercise-days 389 16.7
3 High: >0.16 exercise-days 389 16.7
TRIPS‘" 1 None: No trips takene 1923 82.5
2 Low: >0 and $0.01 trips off 211 9.1
3 High: >0.01 trips off 196 8.4
DAYSOFF" 1 None: No horse-days off’ 1928 82.7
2 Low: >0 and $0.03 days off 192 8.2
3 High: >0.03 days off 210 9.0

 

a Admitted to the starting multivariable model because it passed screening
(p<0.50). b Maintained in the final multivariable on a priori grounds.c Excluded
from the starting multivariable model due to the potential for multicollinearity.
d Exercise or performance days per total horse-day available to exercise. 6 Trips
off operation per total horse-days monitored. ‘ Days off operation total horse-
days monitored.

114

Multivariable logistic-binomial regression for distinguishable data was
conducted at the individual-animal level (Table 4.4). The activity risk factors
(RACE, SHOW, and OTHER), age (AGE), and sex (SEX) were each maintained
in the final model on a priori grounds. The goodness-of—fit of the final model
was evaluated using the likelihood ratio statistic which indicated that there was

no significant difference between the fit of the starting and final models.

115

Table 4.4

Multivariable logistic regression model with random effects of operation- and
individual-animal-level risk factors associated with the occurrence of lameness
in 2,330 horses in 97 Michigan equine operations (1992-1994; Michigan,
USA).

 

 

Risk Factor b SElb) Wald's P RR (95% Cl)
RACE 0.56 0.27 0.039 1.75 (1.03, 2.99)
SHOW 0.37 0.21 0.086 1.44 (0.95, 2.20)
OTHER -0.18 0.50 0.716 0.83 (0.31, 2.22)
EXERCISE: 0.00 -— —— --

None
Low 0.84 0.21 <.001 2.32 (1.54, 3.51)
High 0.91 0.23 <.001 2.48 (1.58, 3.90)
OPERATION SIZE: 0.00 -- -- --
lst Qa
2nd Q —0.86 0.27 0.001 0.42 (0.25, 0.72)
3rd Q -0.55 0.25 0.031 0.58 (0.35, 0.95)
4th Q —0.82 0.42 0.054 0.44 (0.19, 1.02)
AGE: lst Q 0.00 —— -— ——
2nd Q 0.16 0.21 0.462 1.17 (0.77, 1.78)
3rd Q 0.11 0.22 0.625 1.12 (0.72, 1.73)
4th Q -0.00 0.23 0.989 1.00 (0.63, 1.57)
SEX: Mare 0.00 —- —— --
Stallion 0.24 0.23 0.295 1.27 (0.81, 1.98)
Gelding 0.04 0.15 0.785 1.04 (0.77, 1.40)
Random Effects 0.61 0.11 —- --
MODEL Deviance df LRSb (F—S) dfc LRS pd
Final 910.29 2315
Starting 896.80 2306 13.49 9 0.14

 

3 Categories defined by quartiles. b Likelihood ratio statistic. ° Degrees of
freedom difference between starting (S) and final (F) models. d p-value for
Likelihood ratio Chi-square statistic.

 

1 16
DISCUSSION

Study population and design--The overall response percentage of 73%
and participation percentage of 79% of operations completing at least 11
months of data collection in MEMS Phase II indicated that the sample of
operations was relatively representative of the operations contacted initially
(Kaneene et al., 1995b; Ross and Kaneene, 1995). Reasons for non-response
included not enough time to participate or that the operation was going out of
business (Kaneene et al., 1995b)

All horses in participating operations were included in the study
population. Overall, the total number of horses (3,925 horses) and the total
number of horse-days monitored (814,753 horse-days) was higher than
reported in previous studies. Jeffcott et al. (1985) conducted a prospective
study of equine health problems on 6 Thoroughbred training stables in England.
Their study was conducted in two rounds of 8-month periods of data collection.
The total number of horses monitored was 581 accounting for 114,933 total
horse-days monitored. Kobluk et al. (1990) reported that during an 81-day
data-collection period 95 Thoroughbred horses from 11 race training stables
were monitored for 5,700 total horse-days. Although the MEMS Phase-ll study
was larger than previously reported studies, it was not limited to racing stables
and Thoroughbred racehorses.

Because of the large number of equine breeds represented in this study,
5 breed categories were developed based on conformation, activity types, and

population size. The types of activities in which horses participated were also

117

diverse. Because some horses engaged in several different types of activities
(either simultaneously or throughout the study period), evaluation of the impact
of activity could not be made using mutually exclusive categorization. Also,
due to modifications in data-collection instruments between the first and
second rounds of the MEMS Phase-ll study, activities were not recorded in a
similar fashion. Therefore, 3 risk-factor groups were created: showing, racing,
and other activities. The types of equine breeds and activities of horses
reported for the study population were similar to those found in the 1991
Michigan equine survey (Michigan Agricultural Statistics Service, 1992)--the
population from which the operations were sampled. However, interpretation
of the analytical results will be limited to the study population.

Limitations in the study design depended largely on the level of
involvement of each operator and their communication with the data collector
throughout the study period. Ultimately, this determined the quality and
amount of data available for each operation. Also, for some of the data
collected it was impossible to discern whether a missing value should have
been interpreted as missing or as a zero value. In these cases, the potential for
misclassification bias existed.

Lameness: Individual-animal level--For the purposes of this study,
prospective identification of lameness cases was important in reducing recall
bias that may occur over a one-year study period. The definition of lameness,
its degree of severity and time to recovery, may have varied between

operations depending on how the lameness affected the expected level of

118

equine productivity. However, a veterinarian was involved in at least 40% of
the lameness cases diagnosed and reported during the study period minimizing
the potential for lack of consistency in lameness definition and diagnosis.
Statistical analyses--To streamline data collection between rounds I and
2, minor changes were made in the data-collection instruments. Because of
this, the availability of some types of data focusing specifically on lameness
varied between rounds. Because the likelihood ratio statistic was to be used
for statistical analysis, it was important to have a complete data set for
comparison of risk factors. Approximately 60% of the horses monitored had
complete data sets for the risk factors of interest in this investigation,
representing 70% of the operations monitored. Comparison of the complete
and incomplete data sets indicated that the population distributions for all of
the risk factors of interest were significantly different. Therefore, interpretation
of the results of the final model may have been biased with respect to the
study population due to the exclusion of those records having missing data.
Further investigation into the composition of the incomplete data set
revealed that 32.9% (525/1,595) of the records were from two operations
alone, each of which had minimal or no health (lameness) data reported. These
operations were relatively large having an average daily operation horse-days
monitored of 116 and 161. Therefore, they were considered to be potential
outliers with respect to population size. To evaluate the effect of relatively
large and small operations on the population distributions of the complete and

incomplete data sets, both large and small operations were excluded in a post-

119

hoc analysis. When this was done the risk factors Operation size, whether or
not a horse participated in showing activities, sex, breed group, the number of
trips a horse took off of the operation, and the number of days a horse was off
the operation were no longer significantly different.

Although the population distributions were not uniform with respect to
all of the risk factors of interest, the deletion of relatively large and small
operations created more-comparable population distributions between the
complete and incomplete data sets. Therefore, when evaluating the results of
the statistical analysis conducted on the complete data set, it must be
recognized that interpretation of the results may have been biased by the
removal of records having incomplete data. Yet, because only two operations
played a primary role in creating these population distribution differences, this
bias may not be excessive.

Considering individuals within the operations monitored to be
independent or to have identical distributions with respect to the probability of
the occurrence of lameness would be expected to violate the assumptions
required by logistic regression techniques. We expected that overdispersion
(extra-binomial variation) would exist in the data (Mauritsen, 1984; SERC,
1990; Curtis et al., 1993). Therefore, logistic-binomial regression for
distinguishable data was utilized for modelling (SERC, 1990). The random-
effects term incorporated into the final model was significant (p< .001)
indicating that overdispersion existed in the data. When the deviance of the

model is greater than the degrees of freedom of the model, overdispersion is

120

indicated (Collett, 1991). However, the deviance of the final model was less
than the number of degrees of freedom--suggesting instead that
underdispersion in the data may actually have existed. Future equine studies
should evaluate this condition further to assess the effects of intraherd
correlation, which may be affected by the degree of individualized care received
by horses. Also, the appropriate categorization of horses, their activities and
intensity of exercise, with respect to the outcome of interest should be
evaluated. This may provide a more efficient representation of the data when
utilizing this modelling technique.

In this sample of Michigan horses, participation in racing was associated
with an almost 2—fold increase in the risk of the occurrence of lameness (95%
Confidence Interval (CI): 1.03-2.99). Based on previous studies of equine
lameness, both hospital-based (Mcllwraith et al., 1991; Dyson et al., 1992;
Schneider et al., 1992; Laws et al., 1993; Lillich et al., 1995) and population-
based (Jeffcott et al., 1982; Rossdale et al., 1985; Bell and Lowe, 1986; Hill
et al., 1986; Kobluk et al., 1990; Mohammed et al., 1991; Mohammed et al.,
1992; Stover et al., 1992; Estberg et al., 1993; Lindner and Dingerkus et al.,
1993; Wilson et al., 1993; Johnson et al., 1994; Peloso et al., 1994),
exposure to the strenuous activities required for race training and performing
was expected to increase the probability for trauma or stress-related injury and
subsequent lameness. In a study of injuries reported at racetracks in the state
of California there were fewer catastrophic injuries per racing week with

quarter-mile and harness racing and training compared with Thoroughbred horse

121

injuries (Johnson et al., 1994). Also, there was a proportionately smaller
number of injuries in Quarter Horses compared to Thoroughbreds (Johnson et
al., 1994). It was suggested that training practices and gait may be related to
these differences (Johnson et al., 1994). In our study, harness and flat-track
racing were combined for analysis. In the future, it may be of interest to
evaluate and compare the level of risk of the occurrence of lameness between
each type of racing.

Participation in showing activities tended to be associated with an
increase in the risk of the occurrence of lameness (Relative Risk (RR) = 1.44;
95% CI: 0.95-2.20). The showing category was composed of a wide variety
of activities including western, dressage, eventing, endurance riding. As with
racing, exposure to showing activities would also be expected to increase the
probability of experiencing trauma or a stress-related injury. Few studies have
evaluated the association between risk factors and lameness in horses used for
showing. Hospital-based case studies (Dyson et al., 1994) and descriptions of
lameness and its treatment (Stashak, 1987) are the primary types of
information sources available that describe the presenting signalment and
potential causes of lameness in horses used for showing. Our study was
probably the first to report that showing activities, as well as racing activities,
were associated with an increased risk of the occurrence of lameness. As was
reported for racing, due to the diversity in types of showing activities, it would
also be expected that the types of injury and severity of the subsequent

lameness would be highly variable. Therefore, investigation into the occurrence

122

of lameness within showing activities may be of interest to determine if there
are differences in the risk of lameness occurring between activity types.

Compared to no activities reported, increasing amount of exercise-related
activities was associated with an approximately 2-fold increase in the risk of
lameness (Low: RR=2.32; 95% CI: 1.54-3.51, High: RR=2.48; 95% CI:
1.58-3.90). Comparison of non-active horses to more-active horses was
expected to be associated with an increased risk of lameness. Lindner and
Dingerkus (1993) reported an increase in the incidence of lameness in
Thoroughbred racehorses in the month of March--directly correlated with the
beginning of more-intensive race training. Dolvik (1994) found that the risk of
serous arthritis in the carpal joint of Norwegian coldblooded trotters was
increased if exposed to walking in a jogcart and fast training versus being left
in a paddock in the 2-year-old year. Physick-Sheard (1986a) reported that the
slower rate of attrition observed for trotters was reflected in their longer racing
life, and may partly be explained by the generally less-intensive career of
trotters compared with pacers.

In contrast, Kobluk et al. (1990) reported a negative linear relationship
between exercise score and problem score of racing Thoroughbreds: horses
with fewer musculoskeletal problems were exercised harder and higher-quality
horses clustered in the high exercise-low problem score areas. Kobluk et al.
(1990) concluded that these types of relationships were consistent with their
observation that trainers used injury levels in making decisions about training

programs for horses. Mohammed et al. (1991) reported a negative association

 

123

between the number of seasons racing, the number of starts per year, and the
total number of starts. This again may have indicated that healthier horses
were participating in racing activities at increased levels. These studies focus
primarily on active horses. The ability of trainers to utilize preventive tactics
against lameness may have affected the amount of exposure individuals had to
exercise-related activities and their subsequent risk of lameness.

When compared to operations with an operation size in the in the Ist
quartile (Q), increasing operation size was generally protective (2nd Q:
RR=0.42; 95% CI: 0.25-0.72, 3rd Q: RR=0.58; 95% CI: 0.35-0.95, 4th
Q: RR=0.44; 95% CI: 0.19-1.02). Operation size was assessed because it
was considered to control for the level of management and the operator’s
knowledge of disease diagnosis, treatment, and preventive health care for all
horses on the operation. Ross and Kaneene (1995) reported that when
evaluating operation-level risk factors for lameness, the total operation horse—
days monitored was also negatively associated with the incidence density of
lameness. On larger equine operations, more preventive measures may have
been used to avoid new cases of lameness. Also, more cases of lameness may
have been treated without veterinary assistance, and thus may not have been
reported. In the equine industry, larger operations often contain a high
proportion of broodmares in the population. Broodmares may be at decreased
risk of experiencing lameness as they are not participating in stressful exercise

or performance-related activities. However, even though operations are larger,

124

particularly-active individuals within these operations may still have been at a
higher risk of experiencing lameness due to their occupation alone.

Horses usually enter training for a specific activity between the ages of
2-3 years old, so, it would be expected that younger animals may be at more
risk of the occurrence of lameness. Younger racehorses were reported to
experience the highest number of fatal injuries (Johnson et al., 1994). And,
Lindner and Dingerkus (1993) reported that the largest proportion of racehorses
experiencing training failure due to lameness, infectious disease, and other
causes were 2-year-olds. In contrast, older animals may be at more risk of
experiencing lameness due to the duration of participation in exercise-related
activities and the potential for repetitive type traumatic injury. Studies have
reported that increasing age was associated with an increase in racing injuries
(Mohammed et al., 1991) and severe breakdowns (Robinson et al., 1988;
Mohammed et al., 1992). When age was categorized by 2, 3, and 4 + year-old
groups, both the 2-year-old and 4+ year-old groups had the highest number of
performance days lost due to lameness (Rossdale et al., 1985). At the
operation-level the weighted average age of horses in the operation was not
significant (Ross and Kaneene, 1995). In our current study, although age was
not found to be significant at the p<0.05 level, it was included in the model
as a biological factor describing individuals in more detail. Also, it was
considered to be a confounder because it was associated not only with the risk

of the occurrence of lameness, but with whether or not an individual

125

participated in showing or racing during the study period and with the intensity
at which the individual was exercised.

The sex of the individual was also expected to affect the risk of the
occurrence of lameness. As expected, geldings and stallions tended to have
a higher risk of experiencing lameness compared to mares. Previous studies
have argued that the decreased occurrence of lameness in fillies during their
racing career is associated with the fact that fillies are more often retired early
for breeding purposes--decreasing their risk of exposure to lameness associated
risk factors (Jeffcott et al., 1982; Physick-Sheard, 1986a; Physick-Sheard,
1986b; Lindner and Dingerkus, 1993). Although sex was not significant, it
was included in the final model as a biological factor describing individuals in
more detail. It, too, was considered to be a confounder because it was
associated not only with the risk of the occurrence of lameness, but also with
whether or not an individual participated in showing or racing during the study
period and with the intensity at which the individual was exercised.

Future studies-Future studies should be designed to account for diversity
within operations more specifically. The use of a random—effects term in an
equine study has not previously been reported. In comparison to other areas
of veterinary research (such as dairy herds or swine operations), equine
operations provide a unique analytical challenge in that horses are often treated
as individuals rather than as groups. Operations may have little homogeneity
between individual animals within an operation--especially with respect to

activity types and exercise intensity. This may affect the intraherd correlation

126

for operations which would require reassessment of random effects at multiple
levels within the operation (McDermott et al., 1994). This type of analysis may
provide more-accurate estimates of the risk of the occurrence of lameness in
horses in randomly-sampled equine operations.

In order to characterize the diverse nature of horses within the equine
industry, optimal categorization schemes for risk factors, such as activity,
should be developed. This would provide more-precise descriptions of all types
of activities in which horses participate, in succession or simultaneously, during
the study period. The inclusion of information about training schedules and
about the types of work surfaces provided for training and performance will
help to identify other areas that can be targeted for the development of
lameness prevention protocols. Also, evaluation of the severity of lameness,
the treatments required, the performance or exercise days lost, and the
recovery level achieved should be evaluated to provide more information about

the impact of lameness on horses, equine operations, and the equine industry.

Chapter 5

SURVIVAL ANALYSIS OF RISK FACTORS ASSOCIATED WITH THE
OCCURRENCE OF LAMENESS IN MICHIGAN (USA) HORSES

ABSTRACT
Objective--To evaluate the associations of operation and individual-animal-level
risk factors with the occurrence of lameness in the Michigan horse population.
Hypotheses--An increase in the hazard of lameness is associated with 1) the
type of activity in which horses participate and 2) increasing amounts of
exercise.
Design--Prospective cohort study design.
Source population--The source population included 3,925 horses monitored for
a total of 814,753 horse-days from 138 randomly selected Michigan horse
operations.
Procedure--All horses monitored <60 days were eliminated from the source
population. From that, a prospective unmatched case-control study population
was generated that included all cases and a random sample of non-cases.
Analysis of risk factors associated with the occurrence of lameness was

conducted using Cox’s proportional hazards regression model.

127

128

Results--Horses in larger operations, compared to horses in the first operation
size quartile, were associated with a decreased risk of lameness (2nd Quartile
(Q): Hazard Ratio (HR) =0.57; 95% Confidence Interval (Cl): 0.36, 0.91, 3rd
Q: HR=0.74; 95% Cl: 0.49, 1.13, 4th Q: HR=0.46; 95% CI: 0.28,
0.76). When compared to mares, stallions (HR=1.90; 95% Cl: 1.17, 3.07)
and geldings (HR=1.46; 95% CI: 1.02, 2.09) were at increased risk of
lameness. Compared to horses used for breeding purposes only, those
participating in exercise or performance-related activities including racing
(HR=4.70; 95% Cl: 1.70, 13.03) and showing (HR=2.80; 95% CI: 1.07,
7.28) were also at increased risk of lameness.

Conclusions--Comparison of the results of this analysis with those conducted
using multivariable logistic regression strengthens the argument that there is a
decreased risk of lameness for horses in larger operations and an increased risk
of lameness for active horses exposed to exercise-related activities.
Additionally, this study has suggested that stallions and geldings are at
increased risk of lameness compared to mares.

Clinical implications--Development of improved lameness prevention methods
in the horse industry should focus primarily on horses participating in exercise
or performance-related activities, including both racing and showing, on male

horses, and on horses stabled in smaller operations.

129
INTRODUCTION

The Michigan Equine Monitoring System (MEMS) Phase-ll equine-health-
monitoring study was implemented to evaluate the health problems of horses1
on an industry-wide basis. The MEMS Phase-ll study was based on prospective
daily monitoring of horses in a stratified random sample of Michigan horse
operations (Kaneene et al., 1997a). From this, investigations of the
associations between management and environmental risk factors and the
occurrence of lameness at both an operation (Ross and Kaneene, 1996a) and
individual-animal (Ross and Kaneene, 1996b) level using multivariable analytical
techniques have been reported. However, the amount of time an individual
horse was exposed to the management and environment of the operation
during the study period was not specifically accounted for in these analyses.
Survival analysis techniques are able to evaluate not only the occurrence of a
disease problem, such as lameness, but the relative timing of the event within
the study period as well. Yet, within the livestock industry, few studies have
been done using this type of analysis to evaluate productivity or the occurrence
of disease (Harman et al., 1996a,b,c; Reid and Mohammed, 1996).

The objective of this study was to conduct survival analysis, using Cox’s
proportional hazards regression model, to evaluate the associations of operation
and individual—animal-level risk factors with the occurrence of lameness in the

Michigan horse population. The specific hypotheses to be tested were that an

 

1 The term horse will be used to include any of the family of Equidae

including horses, asses, and zebras.

130

increase in the hazard of lameness is associated with 1) the type of activity in

which horses participate and 2) increasing amounts of exercise.

MATERIALS AND METHODS

Study Design--Details of the design and implementation of the MEMS
study, Phases l and II, have been published (Kaneene et al., 1997a). The
MEMS Phase-II data base was used for the purposes of this investigation.
Details of data-collection methods used for the MEMS Phase-ll equine-health-
monitoring study have been published (Kaneene et al., 1997b). Briefly, the
equine-health-monitoring study was designed as a prospective epidemiological
study. Horse operations, whose operators consented to participate, were
enrolled in the study for 12 months.

Participating operators were interviewed on a monthly basis by a state,
federal, or university veterinarian or animal technician (a MEMS data collector).
Data regarding operation management, operation environment, and other
information not expected to change on a monthly basis were collected at the
beginning (initial management surveys) and at the end of the study (close-out
survey). Horse health status and activities, and operation economic data were
expected to change on a daily basis. These types of data were recorded by
operators throughout each month of data collection. On a monthly basis, the
MEMS data collector for each operation interpreted, summarized, and recorded

these data on data-collection instruments specifically designed for data entry.

131

Definition of a case--For the purposes of this study, a horse was
considered to have a case of lameness if it was reported to have a condition
causing abnormal locomotion in one or more gaits or a problem with
locomotion-associated anatomical structures. Determination that a horse was
lame, the description of the specific type of lameness affecting the horse, and
recovery from lameness was made by the operation owner, veterinarian,
trainer, or farrier and reported to the MEMS data collector. Detailed information
about lameness diagnostic techniques was not available. Confirmation of
diagnoses was not conducted.

Horses that had a lameness problem at the beginning of the study or at
the time of entry into the study population were considered to have a prevalent
case of lameness. Horses that experienced a lameness problem during their
monitoring period were considered to have an incident case of lameness.
Horses may have experienced more than one case of lameness during the study
period, either simultaneously or sequentially.

Unit of observation--The horse-day, representing each day a horse was
monitored during the study period, was the unit of observation. Total-days was
the number of days in the study accrued by the horse between the first date
of entry into the study and the final date of exit. In contrast, monitor-days was
the number of days in the study accrued by the horse between each date of
entry into the study and each corresponding date of exit. Monitor-days did not

include the days that a horse was off of the operation.

132

Outcome variable--Study-days was used as the outcome variable. Study-
days was defined as the total number of days accrued by the horse between
the first date of entry into the study until either the first reported lameness case
(time to event), or the final date of exit or the end of the study period
(censoring date). It is important that although it was not possible to directly
monitor the status of a horse while it spent time off of the operation, study-
days, included days the horse spent off the operation. This was done because
many horses exited and reentered the study population frequently. The days
a horse spent off of the operation were considered to be a reflection of activity,
operation management, and potential risk, in chronological order, with respect
to the occurrence of the first reported lameness.

Risk factors evaluated--Operation-level data characterizing risk factors
potentially associated with lameness were summarized from the initial and
close-out management surveys. lndividual-animal—level data were summarized
from the monthly data-collection instruments. The following is a description of
the risk factors examined and how they were categorized.

The operation size and the turnover of the horse population was
described by the average number of horses in an operation per day. This was
calculated by first computing the total number of monitor-days accrued by
horses in an operation during each month the operation participated in the
study, and second, dividing the total operation monitor-days by the total

number of calendar-days the operation participated in the study. The average

 

133

operation size for individual horses was then categorized by quartiles for
analysis.

Individual-animal-level risk factors focused on the signalment of horses
and the types of activities in which they participated. Signalment information
evaluated included the age (categorized by quartiles: 0—3 years, 4-7 years, 8-
12 years, and 13 + years), sex (mare, stallion, gelding), and breed (grouped by
general phenotype including Quarter Horse types (including Quarter Horses,
Appaloosas, and Paints, etc.), Saddle types (including Arabians, Morgans, and
Saddlebreds, etc.), Standardbreds, Thoroughbreds, Mixed breeds (including
Warmbloods and part-breds such as Half-Arabians, Thorcherons, etc.), and
Other breeds (including Draft horses, Ponies, and Grade horses, etc.)). These
factors were considered to provide a basic description of the horse. The type
of housing (including Inside only, Both inside/outside, Outside only) while in the
operation was also evaluated to assess the importance of the environment to
the occurrence of lameness. The occupation of horses was summarized in two
stages because many horses were reported to have participated in more than
one activity during the study period. First, eleven different activity groups were
constructed from the data and horses were assigned to each one in which they
were reported to have participated in or not (breeding, conditioning, draft,
dressage, driving, hunter, flat racing, harness racing, pleasure, riding, showing,
and western). Finally, these groups were collapsed into five mutually exclusive

activity groups expected to show exposure to more exercise intensive types of

 

 

134

activity: Breeding, Activity not reported, Activities other than racing or
showing, Showing, Racing.

The amount of exercise or performance to which a horse was exposed
during the time prior to lameness or censoring, was measured by dividing the
total number of times the horse was reported to have been exercised and or to
have performed prior to lameness or censoring (work-days) by the study-days.
Evaluation of the number of trips a horse took off the operation prior to
lameness or censoring (trips) divided by study-days was also evaluated. Each
of these risk factors were grouped into 3 categories: None (horses having a
value of zero), Low (a value at or below the median score for all horses having
a value greater than zero), and High (a value above the median score for all
horses having a value greater than zero).

Study population: Criteria for inclusion--To reduce the effect of a
relatively high proportion of censored individuals in the source population, a
prospective unmatched case-control study population was generated for this
investigation. Only the first reported case of lameness for a horse was included
in this study, subsequent lameness cases were not evaluated. When two
lameness cases were reported to have occurred simultaneously, the lameness
problem that was most likely to have made the horse more severely lame was
chosen to represent the first lameness case reported. Horses entering the
study with a prevalent case of lameness were not included in the study
population because they could not be evaluated using our definition of time to

event

135

Because survival analysis accounts for the effect of risk factors
throughout time and because of the types of data available, the values for
many of the risk factors of interest included data for the months prior to, but
not including the month of the lameness case reported. Therefore, horses were
required to have been monitored for at least 60 days, otherwise they were
eliminated from the study population due to the potential for lack of sufficient
data regarding the risk factors of interest.

The study population included all horses that had at least one reported
incident case of lameness and that met the >60 study-day criteria. Also
included was a random sample of horses having no reported case of lameness
and that met the >60 study-day criteria (controls). Controls were randomly
selected, using a table of random numbers, to provide a 1:3 ratio of lame
(cases) to not-lame (censored control) individuals. The 1:3 ratio was selected
to provide increased efficiency in our analysis (Kleinbaum et al., 1982) while
providing a lower percentage of non-lame censored individuals in the study
population.

Statistical Analyses--Summary statistics were computed for each of the
risk factors of interest (SAS Institute Inc., 1996). The likelihood ratio statistic
(LRS) was used for model development. Therefore, it was important to
compare the same data set with respect to the inclusion or exclusion of risk
factors during modeling. Assessment of the differences between individuals
in the source and study populations and those in the study population having

complete and incomplete (missing values for one or more of the risk factors of

 

136

interest) data sets was conducted using the Wilcoxon rank-sum test
(continuous risk factors) and the Cochran-Mantel-Haenszel Chi-square or 2-
tailed Fisher's exact test (categorical risk factors) where appropriate. For the
study population with a complete data set, Spearman correlation coefficients
(r) were computed to identify potential areas of multicollinearity between each
of the risk factors. Also, univariable Cox proportional hazards regression (SAS
Institute Inc. (Proc PHREG), 1992) was conducted for each of the risk factors
to assess their degree of association with the outcome variable and the hazard
ratios were plotted.

A multivariable Cox proportional hazards regression model was then
developed (SAS Institute Inc., 1992). Only those individuals in the study
population having a complete data set were used for multivariable analysis.
Rather than using a fully-saturated model containing all risk factors assessed,
a starting model containing a selected subset of risk factors was utilized
(Collett, 1994). This model contained all operation and individual-animal-level
risk factors considered to be of biological importance and those that had a
univariable model LRS p-value 50.50. Activity, rather than breed, was selected
to represent the types of exercise or performance-related activities in which
horses participated. The model did not contain both activity and breed due to
the potential for redundancy of information and multicollinearity (e.g. no Grade
horses were in the racing category, the majority of Standardbreds were in the
racing category). Two-factor interaction terms in the starting model were to

include those risk factor combinations having expected biological meaning.

137

From the starting model, a backward method of variable evaluation using the
LRS was conducted to assess risk factor inclusion in or exclusion from the final
model (Collett, 1992). Operation size, age, and sex were forced into the final
model to account for potential confounding. The goodness-of-fit of the final
model was evaluated by calculating the LRS between the starting and final
models and comparing it to the chi-square distribution (Collett, 1992).
Deviance and martingale residuals were plotted to identify potential outlying
observations (SAS Institute Inc., 1992). Outliers were to be removed and the
model refit. Ultimately, the most parsimonious model, maintaining operation

size, age, and sex, was chosen to represent the study population.

RESULTS

Source population--The source population has been described in detail
(Kaneene et al., 1997b; Ross et al., 1997). Briefly, a total of 138 Michigan
horse operations participated in the MEMS Phase-ll equine-health-monitoring
study, 77 in round 1 and 61 in round 2 of data collection. The total number
of horses monitored in these two 12-month rounds of data collection was
3,925 (Per operation: Minimum (Min) =1; 25th Quartile (Q) =6; Median=14;
75th Q = 34; Maximum (Max) =423) with an accumulated total operation horse-
days monitored of 814,753 (Per operation: Min=116; 25th Q=1,417;
Median=2,584; 75th O=7,899; Max=58,964).

A total of 382 cases of lameness (prevalent and incident cases) were

reported for 298 horses monitored in 92 operations during the study period.

 

138

A veterinarian was associated with the diagnosis in 213 of 382 (55.8%) of all
lameness cases reported. Of the 280 horses reported to have experienced an
incident case of lameness, 225 (80.4%) had a single case, 38 (13.6%) had 2
cases, 14 (5.0%) had 3 cases, 1 (0.4%) had 4 cases, and 2 (0.7%) had 5
cases. Simultaneously occurring lameness cases were reported for 17 of the
298 (5.7%) horses with a lameness reported.

Study population--The study population was generated by first
eliminating 24 of 3,925 (0.6%) horses reported to have had a prevalent
lameness case and 1,071 of 3,901 (27.4%) horses that had $60 study-days.
From the remaining 2,830 of 3,925 (72.1%) horses, the case-control study
population was selected. The study population contained a total of 620 horses
including all remaining horses with a reported first case of lameness (n =155)
and 465 randomly selected non-case horses, accounting for 172,708 monitor-
days from 109 operations. A total of 3,627 (92.4%) horses were censored of
the 3,925 horses in the study population compared to 465 of 620 (75.0%) in
the study population.

Comparison of source and study population data sets-~The source and
study populations were compared with respect to several of the risk factors of
interest. There was no significant difference in the distribution of horses in the
study population (n = 620) compared to the remaining non-lame source
population (n = 2,210) with respect to: quartiles of monitor-days (p = 0.24), sex
(p=0.37), activity categories (p=0.22) and housing (p=0.33). Although it

was not significant at p <0.05, the study population had a higher proportion of

139

horses in the 2nd and 3rd age quartiles compared to the remaining non-lame
population (2nd Q: 162 of 559 (29.0%) compared to 478 of 1,898 (25.2%)
and 3rd Q: 136 of 559 (24.3%) compared to 418 of 1,898 (22.0%),
resectively) (p=0.09). When age was evaluated as a continuous risk factor,
there was no significant difference between the 2 populations (p=0.53).

There was a significant difference in the distribution of the populations
with respect to operation size categories (p=0.03). In this case, the study
population had a higher proportion of horses in the lst and 3rd size categories
compared to the remaining source population (lst Q: 169 of 620 (27.3%)
compared to 521 of 2,210 (23.6%) and 3rd Q: 176 of 620 (284.%) compared
to 589 of 2,210 (26.6%), respectively). Exercise categories were also
distributed significantly differently between populations (p =0.03). The study
population had a lower proportion of horses in the None category (411 of 620
(36.4%)) compared to the remaining non-lame population (1,568 of 2,210
(71.0%)). In turn, the study population had a higher proportion of horses in
both the Low and High categories (107 of 620 (17.3%) and 102 of 620
(16.4%), respectively) compared to the remaining non-lame population (362 of
2,210 (16.4%) and 280 of 2,210 (12.7%), respectively). The categories for
number of trips taken off of the operation followed a pattern similar to that of
the exercise categories (p=0.05).

Comparison of complete and incomplete study population data sets--
Within the study population, 550 of 620 (88.7%) horses had complete data

sets for the risk factors of interest (Tables 5.1 and 5.2), representing 106 of

 

 

 

140
109 (97.2%) operations. The complete data set included 153 of 155 (98.7%)

first lameness cases in the study population. There was no significant
difference between the complete and incomplete data sets with respect to
monitor—days (p = 0.29), total-days (p = 0.11), or sex (p = 0.38). Because of the
small number of horses with data available in the incomplete data set, accurate
evaluation of the differences between the complete and incomplete data sets
with respect to several other risk factors, including operation size, breed group,
activity category, exercise, and number of trips off of the operation was not
possible.

Statistical analysis--Tables 5.1 and 5.2 provide summaries of operation
and individual-animal-level risk factor data compiled for the 550 horses with
complete data sets. These tables also indicate which risk factors entered the
starting model and which risk factors were maintained in the final model on a
priori grounds. A thorough evaluation of potential interaction terms was
conducted and none were deemed appropriate for entry into the starting model.
All Spearman correlation coefficients between the risk factors of interest were
r<0.5 between each of the risk factors, except for the correlation between
activity category and exercise (r=0.76). Therefore, none of the risk factors
were eliminated from consideration from entry into the Starting model based on
correlation coefficients. Figures 5.1-5.3 Show the hazard ratios and Wald p-
values for univariable models containing activity, breed, and exercise,

respectively.

 

141

Results of the multivariable Cox proportional hazards regression are
found in Table 5.3. During model building, activity category entered the final
model. Operation size, age, and sex were each maintained in the final model
on a priori grounds. Operation size and sex were strong enough to have been
maintained in the final model on statistical grounds as well. No outliers were
identified based on deviance and martingale residual plots. The goodness-of—fit
of the final model was evaluated using the LRS which indicated that there was

no significant difference between the fit of the starting and final models.

Table 5.1

142

Operation and individual-animal-level signalment and housing risk factors
evaluated for 550 horses in 106 operations participating in the Michigan Equine
Monitoring System, 1992-1994.

 

Risk Factor

Description

Cases (%)

Controls (%)

 

Operation level:

 

 

 

Operation sizea lst Q:b 2.17- 13.02 AHPDc 56 (36.6) 84 (21.2)
2nd Q: 13.03- 29.23 AHPD 28 (18.3) 109 (27.5)
3rd Q: 2924- 44.03 AHPD 41 (26.8) 93 (23.4)
4th Q: 44.04-161.54 AHPD 28 (18.3) 111 (27.9)

Individual-animal level:

Agea lst Oz” 0- 3 years 29 (18.9) 97 (24.4)
2nd Q: 4- 7 years 43 (28.1) 114 (28.7)
3rd Q: 8-12 years 48 (31.4) 88 (22.2)
4th Q: 13-37 years 33 (21.6) 98 (24.7)

Sexd Mare 64 (41.8) 220 (55.5)
Stallion 25 (16.4) 45 (11.3)
Gelding 64 (41.8) 132 (33.2)

Breedd Quarter Horse types6 38 (24.8) 139 (35.0)
Saddle types’ 29 (19.0) 79 (19.9)
Standardbreds 11 (7.2) 42 (10.6)
Thoroughbreds 26 (17.0) 42 (10.6)
Mixedg 44 (28.7) 74 (18.6)
Otherh 5 l 3.3) 21 (5.3)

Housingi Inside only 58 (37.9) 179 (45.1)
Both inside and outside 74 (48.4) 154 (38.8)
Outside only 21 (13.7) 64 (16.1)

 

 

3 Passed initial screening (p < 0.50) and maintained in the final model on a priori
grounds. b Quartile. ° Average horses per day in the operation. d Passed initial
screening (p<0.50) but excluded from the starting model due to the potential
for multicollinearity. " e.g. Quarter Horse, Paint, Appaloosa. ‘ e.g. Arabian,
Morgan, Saddlebred. 9 e.g. Half-arabian, Thorcheron. " e.g. Grade, Draft,
Pony. ‘ Admitted to the starting multivariable model because it passed
screening (p<0.50).

143

Table 5.2:
lndividual-animal-level activity risk factors evaluated for 550 horses in 106
operations participating in the Michigan Equine Monitoring System, 1992-1994.

 

 

Risk Factora Description Cases (%) Controls
(%)
Activity Breed: Breeding purposes only 5 ( 3.3) 34 ( 8.6)
NSA: No specific activity 65 (42.4) 225 (56.6)
Other: Activities not race,
Show, or breedlo 33 (21.6) 61 (15.4)
Show: Showing activities0 33 (21.6) 61 (15.4)
Race: Racing activitiesd 17 (11.1) 16 ( 4.0)
Exercise NonezNo exercisee 76 (49.7) 272 (68.5)
Low: >0—0.13 exercise days 38 (24.8) 63 (15.9)
High: >0.13 exercise days 39 (25.5) 62 (15.6)
Trips None:No trips offf 105 (68.6) 322 (81.1)
Low: >0-0.01 trips off 28 (18.3) 34 ( 8.6)
High: >0.01 trips off 20 (13.1) 41 (10.3)

 

a Admitted to the starting multivariable model because it passed screening
(p<0.50). b e.g. driving, draft, riding, or conditioning activities. ° e.g. western,
dressage, or hunter-jumper activities. d e.g. flat or harness racing. ° Exercise
days per days available to exercise. ’ Trips off operation per horse-days
monitored.

144

16.0 -
14.0 -
12.0 -

Hazard 10-0 '
Ratio 8.0 - .- ..

(HR) 6.0 -
4.0 -

2.0 -
0.0 W "

Breed NSA Other Show Race
Activity

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 5.1:

Univariable hazard ratios (HR) and 95% Confidence Intervals (error bars) for
Activity categories: non-exercise related activity (Breed), no specific activity
reported (NSA), activity other than showing or racing (Other), showing (Show),
and racing (Race). * = significantly different (p<0.05) from the Breed
category.

145

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3.50 - .,*
3.00 -
2.50 - ..*

Hazard 200 _

Ratio --

(HR) -
1.00 -
0.50 -
0.00 I I I I I I

QHT THB STB SDT MIX 0TH
Breed
Figure 5.2:

Univariable hazard ratios (HR) and 95% Confidence Intervals (error bars) for
Breed groups: Quarter Horse types (QHT), Thoroughbreds (THB),
Standardbreds (STB), Saddle Horse types (SDT), Standardbreds, Mixed (MIX),
and Other (OTH). * = significantly different (p<0.05) from the QHT category.

146

3.0 -
2.5 -

2.0 -
Hazard

Ratio 1.5 -
(HR) "

 

 

 

 

 

0.5 -

 

 

 

 

 

 

 

 

0.0 . . .
None Low High

Exercise

Figure 5.3:

Univariable hazard ratios (HR) and 95% Confidence Intervals (error bars) for
Exercise Levels: No exercise reported (None), exercise at or below the median
for all horses having an exercise value greater than zero (Low), exercise above
the median score for all horses having a value greater than zero (High). * =
significantly different (p<0.05) from the None category.

147

Table 5.3:
Multivariable Cox proportional hazards model of operation and individual-animal-
level risk factors associated with the occurrence of lameness in 550 horses in

106 Michigan horse operations participating in the Michigan Equine Monitoring
System, 1992-1994.

 

 

Risk Factor8 Parameter Standard Hazard Ratio
estimate error (95% Confidence
Interval)
Activity: Breed -- -- --
NSA 0.81 0.47 2.26 (0.89, 5.69)
Other 0.91 0.49 2.48 (0.95, 6.48)
Show 1.03b 0.49 2.79 (1.07, 7.28)
Race 1.55b 0.52 4.70 (1.70, 13.04)
Operation Size: 1st 0° -- -- --
2nd 0 -0.56b 0.24 0.57 (0.36, 0.91)
3rd 0 —0.30 0.22 0.74 (0.49, 1.13)
4th 0 -0.77b 0.25 0.46 (0.28, 0.76)
Age: lst O° -- -- --
2nd O 0.33 0.26 1.39 (0.83, 2.31)
3rd O 0.58b 0.25 1.78 (1.09, 2.91)
4th O 0.25 0.27 1.28 (0.75, 2.19)
Sex: Mares -— -- --
Stallions 0.64b 0.24 1.90 (1.17, 3.07)
Geldings 0.38b 0.18 1.46 (1.02, 2.09)

 

Final model: -2(log(|ikelihood)) =42.9; Degrees of freedom =12; p=0.0001
Likelihood Ratio Statistic = 6.82; Degrees of freedom = 6; p>0.05

a Description of risk factors in Tables 5.1 and 5.2. b p<0.05. ° Ouartile.

148
DISCUSSION

Few epidemiological studies of the risk factors associated with the
occurrence of lameness in horses have been conducted (Kobluk et al., 19903,b;
Mohammed et al., 1991; Mohammed et al., 1992; Estberg et al., 1995;
Estberg et al., 1996; Kane et al., 1996; Ross and Kaneene, 1996a,b). These
studies have relied on data collected retrospectively (Mohammed et al., 1991;
Mohammed et al., 1992; Estberg et al., 1995; Estberg et al., 1996a,b; Kane
et al., 1996) and prospectively (Kobluk et al., 1990a,b; Ross and Kaneene,
1996a,b). Individuals were classified as lame or not lame and the strength of
association between the occurrence of lameness and several risk factors of
interest was evaluated. However, the actual time that horses were exposed to
the risk factors of interest was not addressed. Therefore, in the study reported
here, survival analysis was used to include information about the actual amount
of time a horse spent in an operation (exposure time). This method was able
to include all data pertaining to horses that experienced lameness during the
study period and to individuals that exited the study (or died) before the
occurrence of lameness (censored) (Collett, 1992). Use of this analytical
method was expected to provide a more detailed assessment of the
circumstances associated with the occurrence of lameness.

Model development--Previous studies of lameness using the Michigan
Equine Monitoring System (MEMS) data base have used the entire cohort of
horses monitored (Ross and Kaneene, 1996a,b). In contrast, this study used

a prospective unmatched case—control study design to evaluate the associations

149

between the time to first lameness and the risk factors of interest. This study
design was chosen to reduce the effect of a relatively large number of censored
individuals in the source population (93%) compared to the study population
(75%). As suggested by Prentice (1986), with a disease having a relatively
low rate of occurrence in a population, much of the covariate information about
the non-case population is largely redundant. Therefore, minimal bias should
have occurred by using an unmatched case-control study design. The
distribution of horses in the study population and the remaining non—lame
population was not significantly different for many of the risk factors of
interest, including activity category, the primary risk factor of interest. Further
evaluation of risk factors that had significantly different distributions (operation
size, exercise categories, and number of trips off categories) revealed that there
was no significant difference in the distribution between the control group and
the remaining non-lame population (p =0.69, p =0.66, p =0.95, respectively).
For each of these risk factors, the difference in the distributions was driven by
the proportion of cases found in each category. This suggests that the
randomly selected group of controls was representative of the non-lame
population.

In this study, the outcome of interest was a reported case of lameness.
It is important that the diagnosis of lameness may have been made by the
operation owner, manager, trainer, veterinarian, or farrier. Because diagnostic
confirmation of lameness was not possible, the results of this study represent

cases of lameness as they were perceived by operators to be affecting horses.

150

However, 56% of the lameness cases reported in the study had a veterinarian
involved with diagnosis and treatment. This should have served to minimize
potential bias related to misclassification.

As with the identification of a lameness problem, quantification of the
outcome variable also relied on the level of operator participation. This was
because the date that the lameness was reported was used when computing
the time-to-first lameness. Therefore, this estimate may have been affected by
the frequency that horses were observed for lameness in operations. This type
of information was not available in this study. In general, it was suspected that
this study would have provided an underestimate of the incidence of lameness
and an overestimate of the time-to-first lameness, because mild lameness cases
may have been missed and reports of lameness may have been made only
when they reached a sufficiently severe state to be noticed.

Computation of time-to-first lameness can be somewhat difficult to
define for horses. For example, some horses were enrolled in the study with
an existing, or prevalent, lameness case. In previous studies, after the
prevalent case of lameness had resolved, the horse was placed in the at—risk
population and it was available to have a new, or incident, case of lameness
reported (Ross and Kaneene, 1996b). In this study, because the outcome
variable was defined as time-to-first lameness, prevalent cases were not
considered to be available to become a case after recovery because their time
in the operation and their time to the occurrence of an incident lameness would

not be the same.

151

Horses could also experience more than one incident case of lameness,
either simultaneously or in succession, during the study period. Overall, 20%
of the lameness cases reported for the study population occurred after the
initial case of lameness. In this study, the time-to-subsequent cases of
lameness was not evaluated. There are methods in survival analysis for dealing
with repeat cases of disease (McGilchrist, 1993). However, in this population,
the subsequent lameness cases were not necessarily of the same type, and it
was difficult to estimate the degree of association between the initial lameness
and the occurrence of subsequent lameness.

Compared to other types of livestock, horses often enter and exit an
operation frequently. In the MEMS Phase-ll, horses were not directly monitored
when they were off of the operation. This made it difficult to establish the
most appropriate method to evaluate the time to first lameness. For example,
when comparing two horses that entered the study on the same day, each
becoming lame 75 days later, one may have stayed in the operation resulting
in 75 horse-days monitored and the other may have left for 3 one-week periods
(21 days) resulting in 44 horse-days monitored prior to lameness. The number
of trips a horse took off of the operation and the time spent off of the operation
were considered to be indicative of the activity level of a horse. More trips off
the operation were expected to be associated with an increase in the risk of
lameness, even if attributable to transport alone. Comparison of the time that
individuals were exposed to the operation management and environment may

be misleading if the time to event were reported as 75 horse-days and 44

152

horse-days, respectively, rather than 75 horse-days for each. For the purposes
of defining the time to lameness, there was considered to be an intangible tie
to an individual even while it was off of the operation. Therefore, study-days,
including days a horse spent off of the operation, rather than only the total
number of horse-days monitored, prior to lameness (or censoring) was
evaluated.

In future studies, evaluation of the impact of the loss of cases evaluated
by eliminating all horses with $60 horse-days monitored and those with
prevalent lameness cases will need to be addressed. To do this, the study
design would need to maintain all records on a daily basis, avoiding monthly
totals of the risk factors of interest. Evaluation of the loss of information about
lameness that occurs by not investigating cases of lameness other than the first
case reported will also need to be addressed.

The likelihood ratio statistic (LRS) was used for model development.
Therefore, it was important to have a complete data set for comparison of risk
factors. Approximately 89% of the horses monitored had complete data sets
for the risk factors of interest in the study population. Because of this,
comparison of the complete and incomplete data sets was difficult due to
relatively few horses with an incomplete data set. However, because the time
to occurrence of lameness, the amount of time horses were in the study, and
the sex distribution of the incomplete data set was not significantly different
from the complete data set, minimal bias should have been generated by

eliminating those with incomplete records.

153

Final modeI--The activity category in which horses participated was
significantly associated with the occurrence of lameness. At any given time,
compared to horses that were categorized as being used for breeding purposes
only, there was an almost 5-fold increase in the risk of lameness for horses
participating in racing (95% Confidence Interval (Cl): 1.70, 13.04), followed
by an almost 3-fold increase in the risk of lameness for horses participating in
showing-related activities (95% Cl: 1.07, 7.28). These results are similar to
those previously reported (Ross and Kaneene, 1997a,b), strengthening the
argument that both racing and showing, relatively high stress activities,
increase the risk of lameness in horses.

Horses participating in activities other than racing or showing (Hazard
Ratio (HR) =2.48; 95% Cl: 0.95, 6.48) and horses with no specific activity
reported (Hazard Ratio (HR) =2.26; 95% Cl: 0.90, 5.69) appeared to have an
increased risk of lameness when compared to horses used for breeding
purposes. However, the hazard ratios were not significant at thep =0.05 level.
This is also consistent with a previous study (Ross and Kaneene, 1997b) in
which analysis at the individual level did not show a significant increase in the
risk of lameness for horses participating in activities other than racing or
showing. In this case (Ross and Kaneene, 1997b), the other activity category
included all horses used for breeding purposes and those horses with no
specific activity reported. In contrast, the study reported here provided
separate categories for each. Univariable hazard ratios indicate that other

activities, showing, and racing significantly increase the risk of lameness when

154

compared to breeding (Figure 5.1). However, the category of horses with no
specific activity reported was not significantly different from the breeding
category. This implies that the group of horses with no specific activity
reported were more like horses used for breeding purposes than those
participating in activities other than racing or showing.

Breed group was not evaluated in the model with activity group due to
potential redundancy of information. Univariable hazard ratios indicated that
only Thoroughbreds and Mixed breeds had a significant increase in lameness
compared to the Quarter Horse type group (Figure 5.2). The use of breed
group as a risk factor for lameness is a complex issue because many of the
breeds have individuals participating in different types of activities. For
example, it might be expected that most Thoroughbreds and Standardbreds
would be in the racing category, and therefore have had an increased risk of
lameness compared to Quarter Horses. However, this is misleading because
not all of these horses were used for racing. Of the 16 Thoroughbreds reported
to have either raced, showed, or participated in some other activity, 5 (31.2%)
raced, 6 (37.5%) showed, and 5 (31.2%) did other activities while 17 of 19
(89.5%) of the Standardbreds raced, and only 1 (5.3%) showed and 1 (5.3%)
did another activity. Therefore, because there may be several types of
activities in which horses participate within breeds, specific activity is probably
a better indicator to use when determining the risk of lameness.

The amount of exercise or performance prior to lameness or censoring

did not enter the final model. Previously, increasing amount of exercise was

155

associated with an increased risk of lameness (Ross and Kaneene, 1997b;
Estberg et al., 1995; Estberg et al., 1996b). In the study reported here,
univariable hazard ratios showed a similar trend (Figure 5.3). However, the
method of categorization of activity used in this study increased the correlation
between activity and exercise, increasing the potential for multicollinearity.
When a model was fit with exercise, instead of activity, the risk of lameness
increased significantly (HR =1.7; 95% Cl: 1.15, 2.59) for horses in the highest
activity category. Therefore, although exercise did not enter the final model,
it should not be discounted as an important factor related to lameness.
Operation size was forced into the final model to account for unmeasured
operation management characteristics. When compared to operations having
an average operation size in the 1st quartile (0), increasing size of the operation
was generally protective (2nd 0: HR=0.57; 95% Cl: 0.34, 0.91, 3rd O:
HR=0.74; 95% Cl: 0.49, 1.13, 4th O: HR=0.46; 95% Cl: 0.28, 0.76).
These results are consistent with those in previous studies (Ross and Kaneene,
1997a,b), which reported that 60% of operations having horses used for
breeding purposes were above the median operation size compared to only
39% of operations having no breeding horses reported. It would be expected
that horses involved in breeding would have a lower number of exercise-related
lameness cases and that subtle lamenesses in non-working horses may not be
diagnosed. Also, the decreased risk of lameness on larger operations may have

been associated with the use of more preventive measures to avoid new cases

 

156

of lameness. Furthermore, more cases of lameness may have been treated
without veterinary assistance, and thus may not have been reported.

Age and sex were both forced into the final model to account for
potential confounding. Overall, age, was not significantly associated with the
risk of lameness. This is also consistent with previous studies (Ross and
Kaneene, 1997a,b). However, evaluation of risk ratios reported in a previous
study (Ross and Kaneene, 1997b) and the multivariable hazard ratios reported
in this study (Table 5.3) suggests that there may be an increased risk of
lameness in the 2nd (4-7 years) and 3rd (81 2 years) age quartiles. These are
the quartiles in which are found the most active horses. The sex of the horse
was also found to be significantly associated with the occurrence of lameness.
In this study, both stallions and geldings had a higher risk of lameness than did
mares. Previous studies have argued that the decreased occurrence of
lameness in fillies during their racing career is associated with the fact that
fillies are more often retired early for breeding purposes--decreasing their risk
of exposure to lameness associated risk factors (Lindner and Dingerkus, 1993;
Jeffcott et al., 1982; Physick-Sheard, 1986a,b). Therefore, when assessing
the risk of lameness, both age and sex should not be discounted, especially
because they are confounders of some of the other risk factors of interest,
especially activity and exercise.

The use of survival analysis has provided a mechanism to account for the
time to occurrence of lameness. The direction of the hazard ratios reported in

this study were consistent with the direction of risk ratios reported in previous

 

157
studies using the MEMS Phase-ll data base (Ross and Kaneene, 1997a,b),

strengthening the argument for an association between these risk factors and
the occurrence of lameness. In addition, the use of survival analysis was able
to identify that stallions and geldings were at increased risk of lameness

compared to mares.

,......

Chapter 6

EVALUATION OF FACTORS INFLUENCING RECOVERY FROM AND
DURATION OF LAMENESS lN MICHIGAN (USA) HORSES

ABSTRACT
Objective--To evaluate factors that may affect recovery from and duration of
a case of lameness in Michigan horses.
Hypotheses--Treatment for lameness is associated with 1) increased recovery
rates and 2) decreased duration of lameness.
Design--Prospective cohort study design.
Sample population--The study population included 3,925 horses from 138
randomly selected equine operations throughout Michigan.
Procedure-During two 12-month rounds of data collection, inventory, health,
activity, and economic data were collected prospectively for all horses in each
operation participating in Phase II of the Michigan Equine Monitoring System
study. The methods that were used to treat lameness in Michigan horses were
summarized. Statistical modelling was conducted to evaluate risk factors
affecting recovery from and duration of lameness using multivariable logistic

regression and Cox’s proportional hazards regression, respectively.

158

159

Results--Of 357 incident lameness cases reported during the Michigan Equine
Monitoring System Phase II equine health monitoring study, 280 (78.6%) were
reported to have recovered. The average duration of a lameness case was 43.2
days (1st Ouartile (O): 1, Median (Med): 22, Maximum (Max): 352). A total of
296 of 357 (82.9%) incident lameness cases received some type of treatment.
Of 619 total treatments used, 329 (53.2%) were administered, conducted or
applied by a veterinarian.

Longer duration lameness cases were associated with decreased rates
of recovery (p = 0.04). Horses experiencing Other types of lameness were less
likely to recover than those experiencing Hoof lameness (Risk Ratio (RR) = 0.48;
95% CI: 0.25-0.93). Horses that had participated in exercise-related activities
prior to the lameness were more likely to recover (RR=1.91; 95% Cl: 1.05-
3.50). Treatment of the lameness was associated with an increased likelihood
of recovery (RR=1.82; 95% CI: 0.97-3.45).

Conclusions--Active horses with a lameness case were more likely to recover
and tended to have shorter lameness duration, which may be indicative of
higher levels of health management and earlier treatment. Cases treated for
lameness were more likely to recover, yet whether or not they were treated did
not affect their duration.

Clinical Implications—-lmproved recovery rates should continue as more effective
lameness treatment strategies are developed, especially for lameness cases that

tend to be of longer duration.

160
INTRODUCTION

Lameness was found to have the highest incidence density and second
longest duration of all health problems reported in horses1 during the Michigan
Equine Monitoring System (MEMS) Phase—ll equine health-monitoring study
(Kaneene et al., 1997b). Evaluation of the types of risk factors affecting the
occurrence of lameness or musculoskeletal injury in a population-based study
have been reported (Robinson et al., 1988; Kobluk et al., 1989; Kobluk et al.,
1990; Mohammed et al., 1991; Mohammed et al., 1992; Dolvik, 1994; Peloso
et al., 1994; Estberg et al., 1995; Estberg, et al., 1996a,b; Kane et al., 1996;
Ross and Kaneene, 1996a,b; Ross et al., 1997a). Few population-based
studies have evaluated factors affecting the duration of lameness cases.

The purposes of treating lameness conditions include restoration of
health, decreasing lost performance time, and ensuring that horses achieve
expected levels of performance, or productivity. Most equine lameness studies
evaluate the effectiveness of a specific treatment method used for a specific
type of lameness (Little and Hilbert, 1987; Caron et al., 1990; McllWraith et
al., 1991; Laws et al. 1993; Parente et al., 1993; Wright, 1993; Kawcak and
Mcllwraith, 1994; Hogan and Bramlage, 1995; Vastistas et al., 1995; Tetens
et al., 1997). In these types of studies, effectiveness has been described in
terms of lameness duration and post-treatment performance level. In contrast,

the Michigan Equine Monitoring System data base has provided an opportunity

 

1 The term horse will be used to include any of the family of Equidae
including horses, asses, and zebras.

161

to begin to evaluate lameness treatment methods being used within the equine
industry as a whole and the impact of different factors on recovery and case
duration.

The objective of this paper was to evaluate risk factors that may affect
the recovery from and duration of a case of lameness in a stratified random
sample of Michigan horses. The specific hypotheses were that treatment for
lameness is associated with 1) increased recovery rates and 2) decreased

duration of lameness.

MATERIALS AND METHODS

Study design-Details of the design and implementation of the MEMS
study, Phases l and II, have been published (Kaneene et al., 1997b). The
MEMS Phase-ll data base was used for the purposes of this investigation.
Details of data-collection methods used for the MEMS Phase-ll equine health-
monitoring study have been published (Kaneene et al., 1997a). Briefly, the
equine health-monitoring study was designed as a prospective epidemiological
study. Equine operations, whose operators consented to participate, were
enrolled in the study for 12 months.

Participating operators were interviewed on a monthly basis by a state,
federal, or university veterinarian or animal technician (a MEMS data collector).
Data regarding operation management, operation environment, and other
information not expected to change on a monthly basis were collected at the

beginning (initial management surveys) and at the end of the study (close-out

162

survey). Equine health status and activities, and operation economic data were
expected to change on a daily basis. These types of data were recorded by
operators throughout each month of data collection. On a monthly basis, the
MEMS data collector for each operation interpreted, summarized, and recorded
these data on data-collection instruments specifically designed for data entry.

Definition of a case--For the purposes of this investigation, the study
population included all incident cases of lameness reported in each round of
data collection during the MEMS Phase-ll equine health-monitoring study. A
horse was considered to have a case of lameness if it was reported to have a
condition causing abnormal locomotion in one or more gaits or a problem with
locomotion-associated anatomical structures. Determination that a horse was
lame, the description of the specific type of lameness affecting the horse, and
recovery from lameness was made by the operation owner, veterinarian,
trainer, or farrier and reported to the MEMS data collector. Detailed information
about lameness diagnostic techniques used was not available. Confirmation of
reported diagnoses was not conducted.

Horses that had a lameness problem at the beginning of the study or at
the time of entry into the study population were considered to have a prevalent
case of lameness. Horses that experienced a lameness problem during their
monitoring period were considered to have an incident case of lameness.
Horses may have experienced more than one incident case of lameness during

the study period, either simultaneously or sequentially.

163

The type of lameness case reported was placed into one of 3 general
Area Affected categories: 1) Hoof, including lameness reported to be
attributable to problems associated with structures of the hoof, 2) Leg,
including lameness reported to be attributable to extremity-associated problems
other than hoof problems, and 3) Other, including lameness reported to be
attributable to back and pelvic-associated structures, lameness with no specific
regional association (e.g. exertional myopathy), or lameness with an unspecified
etiology.

Outcome variables--The horse-day, representing each day a horse was
monitored during the study period, was the unit of observation. The total
horse-days monitored was the number of days in the study accrued by the
horse between each date of entry into the study and each corresponding date
of exit. Total horse-days did not include the horse-days that a horse spent off
of the operation.

Recovery from lameness was defined as the operators perception of
whether or not the horse had recovered from the lameness during the study
period. The duration of a case of lameness (time-to-recovery) was the total
horse-days between the first reported date of lameness and the recovery date
or date of censoring reported by the operator. Censoring occurred when a
horse was euthanized, culled or sold, exited the operation, or the study ended
prior to lameness recovery. A horse could experience simultaneous types of

lameness problems and each problem was considered to be a separate case of

164

lameness. Therefore, in some cases, the duration per case may overestimate
the actual duration that the horse was lame.

Risk factors evaluated-4ndividual-animaI-Ievel data were summarized
from the monthly data-collection instruments. The following is a description of
the risk factors examined and how they were categorized.

Risk factors evaluated focused on the signalment of horses and the types
of activities in which they participated. Signalment information evaluated
included the age (categorized by quartiles), sex (mare, stallion, gelding), and
breed (grouped by general phenotype including Quarter Horse types (including
Quarter Horses, Appaloosas, and Paints, etc.), Saddle types (including
Arabians, Morgans, and Saddlebreds, etc.), Standardbreds, Thoroughbreds,
Mixed breeds (including Warmbloods and part-breds such as Half-Arabians,
Thorcherons, etc.), and Other breeds (including Draft horses, Ponies, and Grade
horses, etc.)). These factors were considered to provide a basic description of
the horse. The occupation of horses was summarized in two stages because
many horses were reported to have participated in more than one activity
during the study period. First, eleven different activity groups were constructed
from the data and horses were assigned to each one in which they were
reported to have participated in or not (breeding conditioning draft, dressage,
driving, hunter, flat racing, harness racing, pleasure, riding, showing, and
western). Finally, these groups were collapsed into five mutually exclusive

activity groups expected to show exposure to more exercise intensive types of

165

activity: Activity not reported, Breeding, Activities other than racing or
showing, Showing, Racing.

The amount of exercise or performance to which a horse was exposed
to prior to lameness, was evaluated by dividing the total number of times the
horse was reported to have been exercised and or to have performed (work-
days) by the horse-days available to exercise prior to lameness. Horse—days
available to exercise was calculated by subtracting the total number of days a
horse was reported not to be able to perform as expected (performance-days
lost) from the horse-days monitored ((total horse-days)-(performance-days
|ost)). Exercise was categorized for analysis. Three categories were
developed: None (horses having a value for exercise of zero), Low (a value for
exercise at or below the median score for all horses having a value greater than
zero), and High (a value for exercise above the median score for all horses
having a value greater than zero).

Data associated with treatment of a lameness case included information
about whether or not diagnosis of the lameness was made with the assistance
of a veterinarian or not (Vet Diagnosis), whether or not the horse received
treatment (treat), and the type of treatments used. Because of the variety of
treatments reported, treatments were divided into 3 general categories for
descriptive purposes: 1) Administered Medications (Admin), including
medications administered orally, intravenously, subcutaneously, or
intramuscularly, 2) Procedures (Proc), including examinations, surgery, farriery,

physical therapy, and bandaging, and 3) Topicals (Topical), including

 

 

166

medications applied to the skin or hoof surface. Each of the treatment
categories were further classified into the 3 most common treatment types
found within each category. The 3 most commonly administered medication
treatment types were NSAIDs (non—steroidal antiinflammatory drugs),
Antimicrobials (antibiotics and antifungals), and Steroids. The 3 most common
procedures conducted were Physical Therapy, Physical Examinations, and
Surgical Procedures. The 3 most common topical medications applied were
Disinfectants, Miscellaneous topicals (e.g. liniments, paints, and blisters), and
Antimicrobials (antibiotics).

Statistical analyses--Evaluation of risk factors was performed by
analyzing the data in a prospective cohort-study format. The Statistical
Analysis System for Personal Computers (PC-SAS) was used to compute
summary statistics for the study population (Statistical Analysis Systems (SAS)
Institute Inc., 1996). A p30.05 significance level was used for all statistical
tests.

Because the likelihood ratio statistic was used for modelling, only those
individuals having complete data sets for the risk factors of interest were
evaluated. Therefore, for the risk factors of interest, assessment of the
differences between the study population having complete and incomplete
(missing values for one or more of the risk factors of interest) data sets was
conducted. For the complete data set, Spearman rank correlation coefficients
(r) were computed to identify potential areas of multicollinearity between each

of the risk factors.

 

 

167

Recovery from lameness-—Multivariable logistic regression was used to
evaluate factors associated with recovery from incident cases of lameness
within Area Affected categories (Hoof, Leg, Other) and for all types of
lameness combined (Total) (Proc LOGISTIC, SAS, 1992).

Duration of lameness--Cox’s proportional hazards regression was used
to evaluate factors associated with the duration of incident cases of lameness
(horse-days to recovery) within the Area Affected categories (Hoof, Leg, Other)
and for all types of lameness combined (Total) (Proc PHREG, SAS, 1992).

It is important that the Hazard ratios (HRs) presented represent the risk
of recovery from lameness, as opposed to the more typical use as the risk of
death. Therefore, if the HR is 1, then the risk factor is interpreted to have no
effect on the duration of lameness. However, if the HR is <1, existence of the
risk factor (or, if the risk factor is continuous, an increasing amount of the risk
factor) is interpreted to be associated with an increase in the duration of
lameness (longer horse-days to recovery). In contrast, if the HR is >1,
existence of the risk factor (or, if the risk factor is continuous, an increasing
amount of the risk factor) is interpreted to be associated with a decrease in the
duration of lameness (shorter horse-days to recovery).

Modeling approach--For each model evaluated, all risk factors of interest
were included in the starting model, regardless of univariable results. Activity,
rather than breed type, was selected to represent the types of exercise or
performance-related activities in which horses participated. The starting models

did not contain both activity and breed due to the potential for redundancy of

168

information and multicollinearity (e.g. no Grade horses were in the racing
category, the majority of Standardbreds were in the racing category). Because
of the potential for multicollinearity between activity and exercise, activity, but
not exercise, was selected for the starting model because it was considered to
also indicate if a horse was exercised in some manner. A backward method of
variable evaluation was used to assess risk factor inclusion in or exclusion from
the final models. The goodness-of—fit of both types of models was evaluated
using the likelihood ratio statistic and comparing it to the chi—square

distribution.

RESULTS

The source population for this study was the Michigan Equine Monitoring
System Phase-II population, which contained a total of 3,925 horses from 138
equine operations (Per operation: Minimum (Min)=1; 2nd Quartile (O)=6;
Median (Med) =14; 3rd O=34; Maximum (Max=423)) with an accumulated
total horse-days monitored of 814,753 (Per operation: Min =116; 2nd
0: 1,417; Med =2,584; 3rd O=7,899; Max=58,964). The median number
of horse-days monitored per horse was 214.0 (Min = 1; 2nd Q=59; 3rd
Q=365; Max =366). The source population included a total of 382 cases of
lameness reported for 298 horses monitored in 92 operations during the MEMS
Phase-ll study period. Prevalent lameness cases accounted for 25 of 382

(6.5%) reported cases.

 

 

 

169

The study population included all incident cases of lameness reported
during the MEMS Phase-ll study. A total of 357 incident cases of lameness
were included from 89 participating operations. A total of 96,342 horse-days
monitored were accumulated within the study population. The median number
of horse-days monitored per horse was 365 (Min =4; 2nd O=170; 3rd
O=366; Max:366). Of the 280 horses reported to have experienced an
incident case of lameness, 225 (80.4%) had a single case, 38 (13.6%) had 2
cases, 14 (5.0%) had 3 cases, 1 (0.4%) had 4 cases, and 2 (0.7%) had 5
cases. Simultaneously occurring lameness cases were reported for 17 of 298
(5.7%) incident lameness cases reported. The proportion of recovered cases
and the mean duration of lameness within the Area Affected categories (Hoof,
Leg, Other) and for all types of lameness cases combined (Total) are found in
Table 6.1.

Table 6.1:
Total number of lameness cases reported, percent of cases recovered, and
duration per case, within the Area Affected categories (Hoof, Leg, Other) and

for all lameness cases combined (Total) for 357 lameness cases reported in 89
equine operations (1992-1994; Michigan, USA).

 

 

Area Case Recovered Duration (days)
Affected n (%) n (%) Mean Min Median Max
Hoof 96 ( 26.9) 78 (81.3) 45.3 1 22 352
Leg 149 (41.7) 127 (85.2) 35.6 1 15 360
Other 112 ( 31.4) 75 (67.0) 51.2 1 18 290

 

Total 357 (100.0) 280 (78.4) 43.1 1 18 360

 

 

170

Of 357 incident lameness cases reported, 61 (17.1%) did not receive
treatment of any kind. Within the Area Affected categories, 14 of 96 (14.6%)
Hoof cases were not treated, 23 of 149 (15.4%) Leg cases were not treated,
and 23 of 11 1 (20.7%) Other cases were not treated. One of the 3 types of
treatments (Admin, Proc, or Topical) were used for 196 of 357 (54.9%) cases,
followed by 77 (21.6%) cases receiving two of the treatment types, and 23
(6.4%) receiving each of the treatment types. These trends followed within
the Area Affected categories, except that the Other category had a higher
proportion of cases receiving only one type of treatment (71 of 1 12 (63.4%))
and a lower proportion of cases receiving three types of treatment (1 of 1 12
(0.9%)).

Several different types of treatments were reported to have been used
to treat lameness. The distribution of the 3 most common treatment types in
each of the treatment categories within Area Affected and for all lameness
cases combined is found in Table 6.2. Of 619 total treatments administered,
329 (53.2%) were administered by a veterinarian. Overall, veterinarians
applied 62 of 93 (66.7%) topical treatments, administered 181 of 325 (55.7%)
medications, and conducted 86 of 201 (42.8%) procedures. Regardless of
who treated a case, the proportion of cases recovered was higher for cases
receiving Administered medications (155 of 197 (78.7%)), Procedures (1 16 of
146 (79.4%)), and/or Topicals (66 of 76 (86.8%)) when compared to cases

receiving no treatment (61 of 141 (67.2%).

171

Table 6.2:

Total number and percentage of the 3 most common treatment types in each
of the treatment categories within the Area Affected categories (Hoof, Leg,
Other) and for all incident cases combined (Total) for 357 lameness cases
reported in 89 equine operations (1992-1994; Michigan, USA).

 

Area Affected

 

 

 

 

 

 

 

 

Treatment Type Hoof Leg Other Total
n (%)a n (%)a n (%)a n (%)b
Administered Medications
NSAlec 56 (31.1) 73 (40.6) 51 (28.3) 180 (55.4)
Antimicrobials 28 (41.1) 32 (47.1) 8 (11.8) 68 (20.9)
Steroids 1 ( 2.6) 23 (60.5) 14 (36.8) 38 (11.7) ;
All Othersd 6 (15.4) 15 (38.5) 18 (46.1) 39 (12.0) ’I
Total 91 (28.0) 143 (44.0) 91 (28.0) 325 (100.0)
Procedures Conducted
Physical Therapy 19 (34.5) 22 (40.0) 14 (25.5) 55 (27.4)
Physical Exam 9 (19.6) 17 (37.0) 20 (43.4) 46 (22.9)
Surgery 14 (35.0) 23 (57.5) 3 (7.5) 40 (19.9)
All Othersd 28 (46.7) 23 (38.3) 9 (15.0) 60 (29.8)
Total 70 (34.8) 85 (42.3) 46 (22.9) 201 (100.0)
Topicals Applied
Disinfectant 21 (67.7) 8 (25.8) 2 (6.5) 31 (33.3)
Miscellaneous8 5 (18.5) 18 (66.7) 4 (14.8) 27 (29.0)
Antimicrobials 9 (42.9) 11 (52.4) 1 (4.7) 21 (22.6)
All Othersd 1 ( 7.1) 12 (85.8) 1 (7.1) 14 (15.1)
Total 36 (38.7) 49 (52.7) 8 (8.6) 93 (100.0)
Grand Total 197 (31.8) 277 (44.8) 145 (23.4) 619 (100.0)

 

aPercent for treatment types is row percent. bPercent for treatment types is
column percent. cNon-steroidal antiinflammatory drug. dAll other types of
treatments within treatment category. ee.g. blister, paint, liniment, poultice.

172

Risk factors were evaluated with respect to recovery from lameness. A
description of the risk factors of interest and the distribution of cases (cases
reported to have recovered before the end of the study period) and controls
(cases not reported to have been recovered before the end of the study period
or those that were censored) for all types of lameness combined (Total). is
found in Tables 6.3 and 6.4. The proportion of recovered cases by the duration
of lameness (in quartiles) is found in Figure 6.1. As duration increased there
was a corresponding decrease in the proportion of recovered cases (Mantel-
Haenszel Chi-Square p =0.001).

Risk factors were evaluated with respect to duration of lameness
(categorized in quartiles). The distribution of the duration of lameness differed
significantly depending on whether or not the lameness case was diagnosed
with veterinary assistance (p = 0.001). The proportion of cases diagnosed with
veterinary assistance within lameness duration quartiles is found in Figure 6.2.
As duration increased, there was a corresponding increase in the proportion of
cases diagnosed with veterinary assistance. This trend was statistically
significant (Mantel-Haenszel Chi-Square p=0.001) This trend was similar
within the Area Affected categories, although it was not statistically significant
in the Other category.

The distribution of the duration of lameness differed significantly
depending on whether or not the case received some type of treatment
(p =0.03). The proportion of cases treated within lameness duration quartiles

is found in Figure 6.3. As duration increased, there was a corresponding

173

Table 6.3:

Signalment and activity risk factors evaluated for all lameness cases combined
(Total) for 357 incident lameness cases reported in 89 equine operations
(1992-1994; Michigan, USA).

 

 

Risk Description Caseb Controlc
Factora n (%) n (%)
Age 1st 0": 0—3 years 56(77.8) 16(22.2)

2nd 0: 4-7 years 95(84.8) 17(15.2)
3rd 0: 8-12 years 63(72.4) 24(27.6)
4th 0: 13+ years 66(77.6) 19(22.4)
Sex Mare 113(73.9) 40(26.1)
Stallion 38(77.6) 11(22.4)
Gelding 129(83.2) 26(16.8) l
Breede Quarter Horse typesf 83(83.8) 16(16.2)
Saddle typesg 49(87.5) 7(12.5)
Standardbreds 27(69.2) 12(30.8)
Thoroughbreds 51 (76.1) 16(23.9)
Mixedh 64(71.1) 26(28.9)
Otheri 6(100.0) 0(0.0)
Activity. NSA: No specific activity 166(74.1) 58(25.9)
Breed: Breeding purposes only 10(90.9) 1(9.1)
Other: Activities, not show or
race’ 35(79.6) 9(20.4)
Show: Showing activities" 46(90.2) 5(9.8)
Race: Racing activities' 23(85.2) 4(14.8)
Exercise"e None: No exercisern 115(70.6) 48(29.4)
Low: 0.0-0.13 exercise 81(87.1) 12(12.9)
High: 0.14-1.3 exercise 84(83.2) 17(16.8)

 

 

 

a'p S 0.05;”p 5 0.001. bHorses recovered from lameness. cHorses not recovered
from lameness or censored. dQuartile. eNot included in starting model due to
potential for multicollinearity. fe.g. Quarter Horse, Paint, Appaloosa. ge.g.
Arabian, Morgan, Saddlebred. he.g. Half-arabian, Warmblood, Thorcheron. ie.g.
Grade, Draft, Pony. J'e.g. driving, draft, riding, or conditioning activities. ke.g.
western, dressage, or hunter-jumper activities. 'e.g. flat or harness racing.
mExercise days per days monitored prior to lameness.

 

174

Table 6.4:

Area affected, veterinary diagnosis and treatments evaluated for all lameness
cases combined (Total) for 357 cases of lameness reported in 89 equine
operations (1992-1994; Michigan, USA).

 

 

Risk Factor3 Description Caseb Controlc
n (%) n (%)

Area Affected" Hoof 78(81.2) 18(18.8)
Leg 127(85.2) 22(14.8)

Other 75(67.0) 37(33.0)

Vet Diagnosis" 0: No veterinary assistance 136(85.5) 23(14.5)
1: Veterinary-assisted 144(72.7) 54(27.3)

Treatment' 0: No treatment of any kind 41 (67.2) 20(32.8)
1: At least one treatment 239(80.7) 57(19.3)

Administerd 0: No medicationse 125(78.1) 35(21.9)
1: Medications 155(78.7) 42(21.3)

Procedured 0: No proceduree 164(77.7) 47(22.3)
1: Procedure 116(79.4) 30(20.6)

Topicald 0: No topicalse 214(76.2) 67(23.8)
1: Topicals 66(86.8) 10(13.2)

 

3'p s 0.05; "p g 0.001. bHorses recovered from lameness. °Horses not recovered
from lameness. dIncludes cases that did not receive specific type of treatment,
but may have received one or both of the remaining treatment types; therefore,
not included in the starting model.

175

100.0 -

 

 

 

 

'o 75.0 -
2
o
>
8
a, 50.0 -
n:
0)
a:
g 25.0 -
0
°\°
0.0 - .
1 2 3 4
Duration (quartiles)
Figure 6.1:

Proportion recovered within lameness duration quartiles for all incident
lameness cases combined (Total) for 357 lameness cases reported in 89 equine
operations (1992-1994; Michigan, USA).

 

176

100.0 ,

75.0 -

 

 

5‘ 50.0 -
‘65
>
°\ 25.0 -

0.0 -

1 2 3 4
Duration (quartiles)
Figure 6.2:

Proportion of cases requiring veterinary-assisted diagnosis (Vet Dx) within
lameness duration quartiles for all incident lameness cases combined (Total) for
357 lameness cases reported in 89 equine operations (1992-1994; Michigan,
USA).

177

100.0 -

 

 

 

75.0 -
-o
8

g 50.0 -
|—
°\°

25.0 -

0.0 -

1 2 3 4
Duration (quartiles)
Figure 6.3:

Proportion of cases receiving treatment within lameness duration quartiles for
all incident lameness cases combined (Total) for 357 lameness cases reported
in 89 equine operations (1992-1994; Michigan, USA).

178

increase in the proportion treated. This trend was statistically significant
(Mantel-Haenszel Chi—Square p =0.04). This trend was similar within the Area
Affected categories although it was not statistically significant. The treatment
categories (Admin, Proc, and Topical) tended to have an increase in proportion
treated corresponding to increasing lameness duration, especially Administered
medications (p =0.08) and Procedures (p =0.04); however the distribution of
Topicals was not significant (p = 0.30). Evaluation of Topicals may be hindered
by the fact that relatively few cases were treated with Topicals (76 of 357
(21.3%), compared to Administered medications (197 of 357 (55.2%) or
Procedures (146 of 357 (40.9%).

In general, the distribution of risk factors with respect to duration was
consistent within the Area Affected categories. However, it is important that
the significance levels within these categories were often affected by small
sample sizes. None of the other risk factors evaluated (Age (quartiles), Sex,
Breed, Activity, Exercise, and Area Affected) were found to have significant
differences in their distributions of lameness duration having p-values ranging
from 0.10 to 0.84.

The likelihood ratio statistic was used for modelling the study population
data. Therefore, it was necessary to compare the complete (no missing values
for the risk factors of interest) and incomplete data sets to identify areas of bias
that may be created by only using complete records. However, since only one
case (within the Other category) was eliminated because of a missing value for

age, statistical comparisons were not made. Spearman rank correlation

179

coefficients were computed on the complete data set and no risk factors were
eliminated from consideration based on the size of the correlation coefficient

alone; however, the correlation between activity and exercise level was

r=0.49. The final multivariable logistic and Cox’s proportional hazards

regression models for all of the lameness cases combined (Total) are found in

Table 6.5.

Table 6.5:

Multivariable logistic and Cox proportional hazards regression final models for
all lameness cases combined (Total) for 357 cases of lameness reported in 89
equine operations (1992-1994; Michigan, USA).

 

 

 

 

Logistic Proportional Hazards
ms" Fact" RR3 95% cub p° HR" 95% CI p
Area Affected:
Hoof -- -- -- -- -- --
Leg 1.42 0.71-2.86 0.33 1.25 0.94-1.66 0.12
Other 0.48 0.25-0.93 0.03 0.77 0.56-1.06 0.10
Active° 1.91 1.05-3.50 0.03 1.23 0.96-1.57 0.11
Treat 1.82 0.97-3.45 0.06 0.88 0.63-1.23 0.47
Vet Diagnosis 0.48 0.27-0.84 0.01 0.58 0.45-0.73 0.00
LRSf on 5 df9 0.00 0.00

 

 

 

alRisk ratio. b95% Confidence Interval. °Wald Chi-square test statistic. dHazard
Ratio. °Horse reported to have participated in exercise-related activities
(Activities other than race or show, show, or race) or not. fLikelihood ratio
statistic. 9Degrees of freedom.

1 80
DISCUSSION

The measurement of the outcome, recovery from lameness, is difficult
to establish precisely because of the variety of levels of activities in which
horses can participate. For example, a horse may be too lame to perform (e.g.
race). However, it may be able to function as a riding horse or a breeding
animal. The only information about recovery available was when and whether
or not the horse recovered. It was not indicated if the type of activities in
which the horse participated were altered because of the lameness condition.
It is important that the diagnosis and assessment of recovery could have been
made by the operation owner, manager, trainer, veterinarian, or farrier.
Because confirmation of the diagnosis and recovery could not be made,
diagnostic accuracy and consistency was difficult to establish in this study.
However, 198 of 357 (55.5%) of the lameness cases evaluated had a
veterinarian involved with the diagnosis. This should have served to minimize
the potential bias related to misclassification of the lameness cases.

Overall, 83% of the lameness cases received some type of treatment and
80.7% of treated lameness cases were reported to have recovered. Of 619
treatments, 290 (46.8%) were administered by the operator. The proportion
of cases diagnosed or treated without the assistance of a veterinarian is of
interest as it indicates that the true impact of the lameness problem on equine
operations may be underestimated by studies relying on practitioner or hospital-
based information only. This was reported to have occurred within the dairy

industry. Whitaker et al. (1983) reported that the average veterinary treatment

181

rate for lameness was 6.3% while 18.7% of cows were treated by farmers,
indicating that the true overall incidence of lameness was higher than
previously reported. Murray et al. (1996) also indicated that veterinarians
treated 32% of the lameness cases and farmers and stockmen an additional
46% of the lameness cases.

Summarization of the treatments provided indicated that the majority of
Hoof, Leg, and Other lameness cases received Administered medications,
followed by Procedures conducted, and Topicals applied. Non-steroidal
antiinflammatory drugs (NSAIDs) were the most common agents used for all
lameness cases combined and within each of the Area Affected categories. For
all other types of treatments used, the ranking becomes specific to the Area
Affected. For example, within the Leg category, 31 of 149 (20.8%) of the
cases affected the cannon-bone region alone (e.g. bowed tendons, suspensory
desmitis, and bucked shins) (Ross et al., 1997b). This may have contributed
to the high proportion of cases receiving NSAIDs and Miscellaneous topicals
(e.g. liniment, blister, paints, or poultice). Leg lacerations, accounting for 41
of 149 (27.5%) of Leg cases reported (Ross et al., 1997b), probably also
contributed to the relatively high proportion of surgical procedures, NSAIDs,
and antimicrobials reported in this category. In contrast, physical examinations
were the most common procedure conducted in the Other category. Perhaps
physical examinations were required more often because the lameness was
either more subtle or relatively complex, requiring veterinary assistance with the

diagnosis.

182

Recovery from and duration of lameness is dependent on both lameness
type (e.g. anatomical location) and the complexity of the problem. The rates
of recovery for Hoof- (81.3%) and Leg- (85.2%) associated cases were similar,
and were not significantly different. In contrast, Other types of lameness had
a significantly lower rate of recovery (67.0%). With respect to duration,
lameness cases lasted approximately 1 month on average. Lameness affecting
the leg had the shortest duration, followed by Hoof, and Other types of
lameness. However, these differences were not significant in the multivariable
model. Overall, a decreasing rate of recovery was observed to be associated
with an increasing case duration. This suggests that longer duration cases,
such as observed in the Other types category, may have been more
complicated or severe. Future studies should include a method of assessing the
complexity and level of severity of specific lameness conditions to evaluate the
impact of duration on rate of recovery in more detail.

There was no significant association between age (in quartiles) and
recovery from or duration of lameness. This risk factor did not enter either of
the final models. Other studies have reported that age was not a significant
factor affecting post-surgical performance (Mcllwraith et al., 1991; Hogan and
Bramlage, 1995; Vastistas et al., 1995). In contrast, Wright (1993) reported
that older horses were significantly less likely to recovery after surgery for
navicular disease. However, it was also reported that the period of lameness
prior to surgery affected the prognosis. This indicates that, with respect to

navicular disease, the effect of age should be evaluated in light of the duration

 

183

that the condition existed prior to treatment. In this study, however, lameness
duration prior to treatment was not an issue because only incident cases of
lameness, that did not exist prior to entry into the study population, were
evaluated.

There was no significant association between sex (mare, stallion,
gelding) and recovery from or duration of lameness. This risk factor did not
enter either of the final models. Other studies have reported that sex was not
a significant factor affecting post-surgical performance (Mcllwraith et al.,
1991). However, it was reported that post-surgical racing longevity was longer
in males than females (Laws et al., 1993). This is probably a reflection of
management and economic decisions tending to keep males at the racetrack
longer and to retire mares for breeding earlier, rather than of surgical success
itself (Jeffcott et al., 1982).

Breed of horse was not associated with the distribution of lameness
cases recovered or their duration. This risk factor was not included in the
starting model because of its potential for multicollinearity with activity. Most
of the studies reported have only one breed in the population being evaluated
(e.g. Thoroughbred racehorses). One study did report that, post-surgery, there
was no significant difference in return to previous use between Thoroughbreds
and Quarter Horses (Kawcak and Mcllwraith, 1994).

The activity in which a horse participated and the amount of exercise to
which it was exposed was used as a factor to indicate the type and complexity

of lameness for which horses might be at risk. Also, activity, and fitness, prior

184

to lameness may affect recovery. It was reported that horses racing prior to
their lameness achieved a significantly higher lifetime race mark and higher
lifetime earnings post-surgery than those who did not (Hogan and Bramlage,
1995). However, although there was a relatively high return to racing (86%),
horses racing both prior to and after surgery had slower post-surgical race
times and a decreased performance index (Tetens et al., 1997).

It was expected that more active horses would experience a relatively
high proportion of lameness cases compared to horses not reported to be
participating in exercise-related activities. Yet, only 122 of 357 (34.2%) of the
lameness cases reported were found in the active category (Race, Show, and
Other activities). Furthermore, 104 of 122 (85.2%) active horses recovered
compared to only 176 of 235 (74.9%) horses not reported to be active (No
specific activity and breeding). Overall, more active horses and those with
higher amounts of exercise were more likely to recover from lameness and the
lameness was of relatively short duration. These horses may be experiencing
less complex, more acute, types of lameness. Activity, or exercise level, may
also be a reflection of the fitness level or the health management available to
the horse. Operators have higher performance expectations for more active
horses. These horses may receive a higher level of daily care, more immediate
medical intervention, and appropriate treatment. For example, race and show
horses had relatively high recovery rates. Horses participating in these types

of activities were probably managed and cared for relatively intensively.

 

 

 

 

185

A lower percentage of cases with veterinary-assisted diagnosis were
recovered compared to those that were not (72.7% and 85.5%, respectively).
In the logistic model, the chances of recovery were 50% lower for cases
requiring veterinary-assistance with the diagnosis. Furthermore, the hazard
ratio computed in the Cox’s proportional hazards model indicated that the cases
with veterinary-assisted diagnosis were of significantly longer duration. This
was considered to be indicative of the complexity of the lameness problem (e.g.
required surgery). The complexity and severity of the lameness, as perceived
by the operator, was probably associated with the request for veterinary-
assisted diagnosis.

The main effect risk factor of interest was how treatment affected
recovery from and duration of lameness. It was not possible to evaluate
specific types of treatment and their impact on recovery from or duration of
lameness because use of treatment types was not mutually exclusive.
Regardless of who treated lameness and the types of treatment used, recovery
was higher with treatment than without. However, whether or not a horse was
treated was not associated with a corresponding decrease in the duration of
lameness. Higher rates of treatment were observed for longer duration cases.
This again may be an indication of case complexity and an indication that, as
time passes and cases do not recover, at least one method of treatment will be
attempted. In a study of dairy cattle lameness it was indicated that training

farmers to recognize early cases of lameness and request treatment resulted in

186

a marked reduction in the duration of cases of lameness (Clarkson et al., 1996).
This may also prove to be effective in the equine industry.

Increased rates of recovery without a corresponding decrease in case
duration is an area that could be targeted for further study. The development
of new and more effective lameness therapies (e.g. high recovery rates),
especially studies based on clinical-trial study designs, should be continued.
Studies should also focus on the importance of lameness duration with respect
to recovery rates and the recurrence of lameness. Furthermore, education of
veterinarians and horse owners on the importance of early intervention and
appropriate treatment, regardless of activity type, may help to continue to
improve rates of recovery and to effect a decrease in performance time lost,

and hence productivity, attributable to lameness.

SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS

SUMMARY

This dissertation has summarized the epidemiology of lameness in
Michigan horses. It has focused primarily on describing the magnitude and
severity of lameness in a population of horses and on identifying risk factors
that were associated with the occurrence of, recovery from, and duration of
lameness. The Michigan Equine Monitoring System Phase-ll equine health-
monitoring study was unique in that it was based on a population of horses
within operations that were randomly selected, based on region and operation
size, to represent the distribution of horses in Michigan. Therefore, information
about lameness was provided for a population of horses diverse in activity and
breed. By conducting a prospective cohort study an evaluation of a variety of
equine operation- management schemes and environments and individual-
animaI-Ievel factors--not limited to racing activities or breeds--and their
relationship to the occurrence of lameness was possible. One limitation of this
study design was that it was a general-health monitoring study and data
collection did not focus on lameness alone. Therefore, all potential risk factors

for lameness were not available for evaluation.

187

188
CONCLUSIONS

Unlike other livestock commodities, such as meat or milk, productivity
of horses (e.g. performance) can be difficult to quantify. However, lameness
was found to be an important cause of lost productivity in the equine industry,
especially with respect to the incidence and duration of cases and mortality
rate. Several operation- and individual-animaI—Ievel factors were found to be
associated with the risk of lameness. Operations that had stalls with gravel or
sand flooring (e.g. loose flooring) and stalls bedded with straw were 2 times
more likely to have a reported lameness case, compared to operations using
other types of flooring or bedding. In contrast, there was a 50% reduced risk
of lameness on operations that had dirt or clay flooring in stalls (e.g. medium
flooring). It was also found, at both the operation- and individual-animal-level,
that increasing operation size was associated with a reduced risk of lameness.
This finding may be attributable to the type of health management or
environment available to horses or to the types of horses that are generally kept
in larger operations (e.g. broodmares). It is noteworthy, that operations
perceiving veterinary and farrier services to be important had relatively high
rates of lameness, which may be attributable to improved reporting or record-
keeping systems on those operations.

Operations that had horses participating in exercise-related activities had
an almost 2-fold increase in the risk of having a horse become lame. On an
individual-animaI-level, activity was also associated with an increased risk of

lameness. In particular, compared to all other horses, race horses and show

189

horses were 70% and 40% more likely to experience lameness, respectively.
Furthermore, horses that were reported to have exercised during the study
period had at least a 2-fold increase in the risk of experiencing lameness.
These findings suggest that the risk of lameness is associated with the
occupation of the horse. Using survival analysis, it was also determined that
compared to mares, stallions and geldings have a 90% and 50% increased
chance of experiencing lameness, respectively. This may be attributable to the
types of activities required of males (e.g. racing or performance) compared to
mares (e.g. breeding). Active horses and horses treated for lameness were
almost twice as likely to recover from a case of lameness; however, treatment
did not affect lameness duration. This again may be a reflection of the type of

health care available to horses.

RECOMMENDATIONS

Further, more specific, investigation into the relationship between factors
such as those mentioned above and the occurrence of, recovery from, or
duration of lameness should be investigated. A population-based prospective
cohort study of lameness alone would help to improve the detail of data
available for evaluation. Areas of focus should include collection of more
detailed information about the specific types of lameness reported (e.g.
anatomical location and structures involved), occupation and occupation
changes attributable to health status, training and exercise regimes prior to

performance, and health and environmental management of horses.

 

 

APPENDICES

--p- .

APPENDIX A

MICHIGAN EQUINE MONITORING SYSTEM

ROUND 1:

DATA COLLECTION INSTRUMENTS

190

MICHIGAN EQUINE MONITORING SYSTEM PROJECT

Doannentafion of Reasons for Refusal to Participate in the Project (1992)

MEMSdatacollector #__:___
Regionofoperation: MDC#__:___

Sizeofoperationindieatedonhbel:__(l°,20,30)
Totalmnnberofhorsesonopemfionattimeofrefiml‘

Person contacted (stategfigofeonmifmorethanoneoontamd)
a. Owner

b. Manager

c. Owner/manager

(1. Trainer

6- Other (specify)

Typeofoperationkheckpredorninanttype)
_ a. Boarding

_b. Brwding
__ c. Training(raoe)

 

d. Training (show)
e. Pleasure

1’- Other (madly)
Predominant breed

 

 

Smtethereasonsgivenbytheopemmrforrefmalmleasenymgiveasoompletean
answer(s)aspossible)

Thereasonsstatedin#7arethoseofthe0perator. Whatinmwiniomwerethe
reasonsforrefnsal.

 

191

Equine Operator Number

 

MICHIGAN EQUINE MONITORING SYSTEM (MEMS) MUTUAL AGREEMENT

Michigan State University (MSU), the Michigan Department of Agriculture (MDA), the
United States Department of Agriculture (USDA), and the equine Operator hereby enter
into this AGREEMENT, the terms of which are set forth below. _

1.

MSU, MDA, USDA will provide personnel who will be referred to as MEMS DATA
COLLECI‘OR (MDC). The MDC and the equine operator will participate together
in implementing a statistically valid MEMS for determining estimates of rates and
costs of equine health events.

The equine operator will maintain a daily diary of equine inventory, health events,
and associated costs.

The MDC will complete person-to-person interviews with the equine operator and
collect information from the equine operator at the monthly visits.

IheequmeOpemtorwfllassistthelldDbeprovidinginformationregarding
economies, management, and disease control. -

TheMDCwfllkeeptheofiginofthedamgnfiggng'glbyrecordmgthedamwiththe
equine operator’s code number only. The MDC will assign a code number to the
equine operator, but will not keep any key to the code after the data collection
period. With the equine operator’s wnsent, the MDC may consult with the equine
operator’s private veterinarian(s) about the health records and associated costs of the
horses in the stable.

The MDC will not ask questions regarding reportable animal diseases. Information
requestedinMEMSwillngtbeusedforregulatorypurposes. '

MSU, MDA, or USDA may publish, or authorize the publication of by others, the
findings acquired from MEMS for the benefit of the equine industry, private industry,

veterinary medicine, and other interested groups, but will ensure that the identity of
the equine operator is not revealed.

The MDC will provide the equine Operator with a report containing results of data

collected, as well as comparisons to other operators in the state, without revealing the
identity of any equine operators participating in MEMS.

Page 1 of 2

10.

192

The equine operator will complete an evaluation of the program upon receipt of the
completed report. ‘

The efiective period of this agreement shall be from

 

 

 

 

month/year
through .
month/year
MEMS Data Collector date

 

 

Equine Operator ' date

Page 2 of 2

 

 

 

193

oesrumon MANAGEMENT SURVEonr : :4 on 1 119

NOTE: The term HORSE implies inclusion of donkeys, mules, ponies, and miniature horses.

 

A. DESCRIPTION OF OPERATION

Annual Percentage of Operation By:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Income Time 4‘ Horses Other:
1. Boarding 96 96 96 96
a Breeding as 96 96 96
3. Training - Show 96 96 96 96
, 4. Training - Race 96 as 96 96
5. Training - Other 96 96 96 96
Specify:
6. Racing - Specify: 96 96 96 96
7. Work (draft) 96 96 96 96
8. Lessons % 96 96 96
9. Handicapped/Therapeutic 96 96 96 96
10. Pleasure 96 96 96 96
11. Horse Sales/Auction Barn 96 96 96 96
12. Riding Stable/Horse Rental 96 % 96 96
13. Other - Specify: 96 96 96 96
Total 96 (Each Must be 100%) = 96 96 96 96
fl 8. OPERATTON INVENTORY # ' Total Value
HorsesownedbytheOperation 'otHorses . S

 

Stabled OFF Operation
(as of Feb. 1. 1992)

C. MANURE MANAGEMENT
1. Hauled away (not sold):

2. Spread for own use:
3. Composted for own use:

4. Sold
a. Composted:

b. Not Composted:
5. Other:

 

l==

 

14 l

194

OPERATION MANAGEMENT SURVEY for : : , on i [19

0. SERVICES UTIIJZED:

1. Veterinarian: Onasealeoii -4.howimponamareeachoimeiolimvingintheveterinaryseMcesyou
purchase? (N/A means not applicable to this operation)

N/A Not Important Very Important

a) disease diagnosis 0 1 2 3
b) Treatment 0 1 2 3 4
c) Nutritional consultation 0 1 2 s 4
d) Preventive health care 0 1 2 s 4
e) Reproductivework o 1 2 3 4
1) 'Source or drugs 0 1 2 a 4
g) Dentistry 0 1 2 3 4
h) Reguariy Scheduled Visits 0 1 2 3 4
l) W Examinations o 1 2 3 4
i) Emergencies o 1 2 3 4
it) Other: 0 1 2 3 4

2. Farrier: Onascaied1-4.howinpomuameadidmetonowhghiarnerseMcesyouutirae?
WAmeartsnotappircabletomisoperation)

NIA Notimportant Veryimportant

a. Professorialatired)

1) trimonty o 1 2 3 4

2) ehoeandtrim o i 2 a 4

3) shoelngonty 0 1 2 3 4

4) consdtationonly o 1 2 3 4
b.1Ftesident(operationstaii)

1) trlmoniy O 1 2 3 4

2) shoeandtrim 0 1 2 3 4

3) shoeingonly o 1 2 3 4
c. Other(speciiy): O 1 2 3 4

 

3. Person responsible for:

a
b. Veterinarian
c. Operation

d.

e. T

1. Other (specify)

Not Applicable

 

 

 

195

DISEASE MANAGEMENT SURVEY for : : , on 1 [19

NOTE: The term HORSE implies inclusion of donkeys, mules, ponies, and miniature horses.
A. GENERAL DISEASE PREVENHON
1. Speedy any health restrictions required for horses to enter the operation:
_a. Negative Coggins Test
_b. Vaccinations:

 

 

Spear
_c. Negative Uterine Culture (broodmares)
_d. Deworrntng

Specify-
_e. Other

SW

 

 

2 DoyouroutineiyisoiateiromthereaottheherdflY/N)
horsesretumirigfromtracklshow
newhorses(purci'tasedornewboarders)
ctitsidebroodmares
horseswithhighiever.ccugh.orsnottynose
summary)

In In In '9 In

3. Isolation Methods W
_3- Special facility/ham
_e. kept in stall
_c. kept in pastime/paddock
_<1 other (specify):

 

 

 

 

 

4. Forhowlongaperiodareindividuaisisolated?

 

8. GENERAL DISEASE MANAGEMENT

1. Do you have isolation procedures for sick animals? Y_ N_
_a. Separate facility

_b. isolation within main facility (describe):

 

 

_c. omertspeciyl

 

2. Do you clean the area where a sick animal was previously stabled? Y_N_
a. Describe method:
b. Type of disinfectant:

 

 

A w ._ .- q...'=l__v_ .hv. “

196

DISEASE MANAGEMENT SURVEY for g : , on t [19

3. Howdoyoudtsposeothorsesthatdieonyouroperation? (checkallthatappiy)
_a. DUN
_b. cremation
_c. haul away/rendering
_d. compost
_e. send to university/necropsy
_1. other (describe)

4. Wdoesmeopammbdbveammetopmehedthpmummahmeocwmdmmeopemionmme
pastfiveyears?Listinorderotmostimportant(a)toieastimponant(e)

 

 

 

wheel»

 

5. Whmdoesmeopemwbeliwetobemetopmmahhpmuemafleaingmeequhehdtmm Listinorder
oi most important (a) to least important (e)
a.

 

 

 

 

9999'

 

-...-e.oys_- . .m —

197

MEMS Initial Building Inventory for Operator:

of

l. TypeoiBuilding:
A.FoleBam

B.Shed
'c. WoodenBarn
o. Converted

E.Other

ii. Building construction:
A. of stnicture:

B. Mainrooi

C. Ceiling height
1. Maximumwhereanimalswilibehwsed:

2. Minimum where animals will be housed:
D. Foundation size

E. 9601 usediorhorseoperation
F. Numberofwaiis

G. Wall construction:
1. Wood

2a. Sheet metal
b. Covered sheet metal
3.
4.
5. Other

H. - Describe the main floor (cement. dirt.

l. Climate Control
1. lsthe barn heated

2. is the barn insulated

3. Ventilation:
a. Number of fans:

b. Number of vents:

0. Doors < 5’ wide available for ventilation

d. Doors 5' wide available for ventilation

e. Number of windows available for ventilation:
1. Other

ill. Stabling Arrangements
A. Total Number of indoor units:

1. Number which to interior:

2 Number which open to building exterior:

. Date: _LJ__

 

“901...“-

198

MEMS initial Building Inventory tor Operator: Paco 2_ or _

of

B. Level‘n building: Enter # otstals:
1. At level

2. Below level bank
3. Other

C. Aisieways: Enter a of aisles:
1. Center aisle on

2. Side
3. Other
4. No aisles
5. Major

D. Stalls (enter number of stalls)
1. Stall Interiors Materials
a. Wood

i. Protective

ii.Treated
b.l. Sheetrnetal
ii. Coveredaheetmetal

c. Chaintence

d. Wovenwlretence
e. Gates/welded

l. Other

2. Describestaililoor

3.:meaI'B
a Solid

b. work bars. etc):
’ c. Combination
d. Other

4. Sidewailaare
a. Solid

b. work
c. Combination
d. Other

D. Stalls (continued)
5. Doors are
a. Solid
l. Full door

ii. Hall door only

 

199

 

 

MEMS Initial Building Inventory for Operator: 9.90 3_ ot _
‘ ' ' Build' Build' ' .
Description of Buildings Building _ Building _ ing _ lng _ Building _

 

detains (continued)
b. Open work doors (lence. bars. etc)
l. Full door

 

a. l-lalldooronly

 

c. Split doors (Dutch doors)

 

iBotl'ihalvessolid

 

ii'Sorrd/Open work

 

it‘i. Bothhaivesopenwork

 

d. Stallguard/chestgateonly

 

e. Other (describe):

 

6. Physicalcontact
-a. lsthereenycontactbetweenhorseswhen
theyareintheirstailsW/N)?

 

b. if yes, describe:

 

7. Bedding
a. Frequency of cleaning (describe):

 

o. Materiaisusodanirorstaiis)
LStraw .

 

ii.Sawdust

 

in Woodshavings/chips

 

iv.Sand

 

v. No bedding

 

vi. Other (specify):

 

V. Indoor Watering Systems
A. Water Sources
1. Well water

 

2. Municipal water system

 

3. Other (specify)

 

B. Sanitation
1. Method (describe)

 

2. Routinely: Frequency

 

3. After disease problem only:

 

4. Notdone

 

5. Other (specify):

 

lV. Watering Systems
C. Individual watering iacilities
1. Buckets (number and daily capacity)

 

2. Automatic waterer (number)

 

 

3. Other (specify):

 

 

 

 

 

 

 

200

MEMS lnltial Building inventory for Operator: Page 4_ of _

 

Descriptionof

D. Group watering facilities
1. Tanks and

zeuckeis and

awornaticwaterers

4.0ther

v. FeedingSystems

A. lndoorlnd‘rvidualfeeding

1. aLooseon
b.Containeron
cCorttainerofl
d.Other
tLooseon
b.00ntaineron
cCoruinerolf
d.Other

groupfeeding
aLooseon

b.Containerson

cCoritainersoll

d.Other
aLooseon
b.00ntainerson
cCoritainersoff
d.Other

Vl. Ancillarylacilitlesinsidebullding:
A.Arena:Number:

1. Dimensions

2. Arena surface sawdust.
8. Round Number:

1. Dimensions

2. Pen surface sadeISi.
C. Other

1. Dimensions

2 Surface (sand. sawdust. etc.)

   

201

MEMS Inltlal Pasture Inventory for Operator:

Front Page _ of _

 

Descriptions of Pasture

 

A. Total Acres:

 

B. Pasture Growth:
a. What is the primary forage growing in this
pasture?

 

b. What is the secondary forage growing in this
pasture?

 

c. Other features of pasture: (YIN)
Cneek(s)

 

 

Pond(s)

 

16 Pasture that is wetlands/marsh:

 

96 Pasture that is brush:

 

inept»:-

96 Pasture that is trees (identify predominant
variety oftrees)

 

%Pasturethatlsbare(noforage.trees.
brush. water. etc): _

9’

 

C. Total linear feet to enclose the pasture:

 

Fencing type: indicate iii feet. and if electrified:
Wooden Board or Rail

 

Steel Pipe or-Rod

 

Rubber

 

Smooth Wire

 

99.0.69

Barbed Wire

 

Chain Link

r.

 

High Tensile anciude ii‘ strands)

 

.313

Woven / Page Wire

 

'L Welded / Hog Panel

 

j. Other (please specify)

 

k. None (explain why)

 

D. Pasture Planting/Seeding:
a If you seed this pasture, identify the plants
seeded (or NATURAL if no seeding occurs):

 

b. How often is the pasture seeded?

 

E. How often do you mow this pasture per year?

 

F. Pasture Conditioning:
a Describe methods used for conditioning this
pasture (e.g. harrowing. fertilizer. etc):

 

b. How often is this done?

 

 

 

 

 

 

COMPLETE BACK OF FORM -> -> ->

Pasture _ Pasture __ Pasture _ Pasture _ Pasture _

 

202

MEMS Initial Pasture Inventory for Operator:

Back Page _ of _

 

Descriptions of Pasture (cont)

Pasture _ Pasture _
—

 

G. Pasture Hygiene:
a. Describe pasture hygiene practices (or NONE):

Pasture
—

Pasture _ Pasture _

 

b. Howoitenarethesepracticesdone?

 

H.AnimaIUse
a. Hewionghasthispasturebeenusedfor
horses? .

 

b. Whenisthispastureusedforhorses(months):

 

c. Otherspeciespastured.with_horses:

 

LPastureRotation:
a. lsthispastureinarotationprogram?

 

b. Howoftenisiirotated?

 

c. Whatotherspeciesmakeuseofthispasture
MienltisofI-rotationforhorses?

 

d. Howmanyotherpasturesgothroughthis
rotation?

 

J. Structures (identify ill and capacity)
a. Shed (Ci—sided structures):

 

b. Lean-to (1-2 sided structures):

 

c. Other(pleasedescribe):

 

K. Watering In the Pasture
a. Describe watering system sanitation. and
frequency

 

b. Natural (ponds. creeks. etc.)

 

c. Tanks (number and daily capacity)

 

(1. Individual buckets (number and daily capacity)

 

e. Automatic systems (number and daily capacity)

 

1‘. Other (describe. with number and daily
W)

 

' Q. Is water heated in winter.

 

L Feeding in the Pasture

3. Supplemental Forages
1. Loose on ground

 

2 In a group feeder

 

3. Other (describe)

 

 

b. Grain Feeding
1. Loose on ground

 

2 In a group feeder

 

3. In individual feeders

 

4. Other (describe)

 

 

 

 

 

 

 

4
:1
I
|
1

M2,? “ET-”f ‘—‘ .- ,-..‘.~

203

MEMS Feeding Management Survey for Operator Page 1 of 3

 

NOTE: The term HORSE implies inclusion or donkeys, mules, ponies, and miniature horses.

I. Grains Fed (If possible. attach feed tags and/or ingredient lists whenever possible)

A. Grain Mixes IDS/100 lb. inlx lbs ml! in stock

1.a Primary Commercial Mix
Brand name:
Price per cwt:

1.b. Secondary Commercial Mix
Brand name:
Price perorvt:

2.a. Primary Own Mix
Name:

 

8. Grain Storage
1. Average amount of grain stored (complete most appropriate line):

a One week supply: lbs stored
b. One month supply: lbs stored
c. _ month supply: lbs stored
d. Other (specify):

 

204

MEMS Feeding Management Survey for Operator , cont. Page 2 of 3
I. Grains Fed

8. Grain Storage (continued)

2. How Grain ls Stored [Uncovered Closed / Covered
A. Bags:
1. Paper
2 Cloth

3. Plastic
4. Other:
B. Bins/Barrels:

1. Metal
2 Wood
3. Plastic
4. Other:

C. Silos

D. Cribs

E. Other:

 

t-Enteraglfpialngrainisuondflrkwaneruarauifgralnmlxisstoredthisway
II. Supplements (If possible, attach reed tags and/or ingredient lists whenever possible)

A. Name the in stock Price/lb

 

 

205

“T'— —:.—

MEMS Feeding Management Survey for Operator , cont.

Ill. Hay

Page30f3

 

A. Hay Storage
(enter # bales)

Form Available (for bales, enter lbs/bale)

 

Square
Ibo/bale

Small Round
lbs/bale

Largo Round
lbs/bale

Loose

Other:

 

1.Typeofl~lay:
aGraas

 

b. Legume:

 

0. Mixed

 

d.Other:

 

260urces:
aRaisedbyoperation

 

b.Purchased

 

3.Storage A, ..
alndoor .
i.Buiiding~nohorses(Y/N)

 

a. Building - with horses
Barn #8:

 

aaSeparatefromhorses

 

bb.AbovestaIls

 

cc.AtstaIllevel

 

dd.Other:

 

b. Outdoors
i. (Covered

 

ii. UHOOVBde

 

 

l'i'tOther:

 

 

 

 

 

 

B. Capacityto store hay:
1._One week supply,
2._Onemonthsupply,

3. _ One year supply,

Q' E

 

4. __ Other (specify)

 

206

 

MEMS Training/Conditioning Programs for Operation

Training l=or‘ Avg. Age’ Mediod’ s Hours/Week for Training at this Leval:‘

(describe) Starts (describe) LOW Moder-to Hieh

 

7 - Enter the activity for which this mining is being used (racing, dressage, etc)

2 - Enter the average age a horse is when they begin using this training method

3 - Enter the training/condiu‘oning method used (Iungeing, treadmill, etc)

4 - Enter the average number of hours a weak a horse uses thB training/conditioning

method for either low, moderate or high stress (or work) levels. These levels are
determined by the m.

 

—-=.~'.T::_'-.'.~~ ‘r, ,- - ~-_-.-‘ ,74

207

MEMSBamSheetiorDaflyActivmesonOperatlon

Date Caution/8m Horse ID Activity Costs Income Labor
or I! head Hrs

 

208

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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213

for the Month of

 

MEMS Monthly Feed and Group Treatments for Operator:

1. FEEDING GROUPS: Enter lbs/horse/dey, or F0 for free-choice (ad lib) feeding

Feed , Grains:

Group Pasture Grass

 

'-§rouporind~iduailyfedorwatered. ifbothareused.entere_3_for§oth

2. PASTURE MAINTENANCE AC'HVITIES:

Pasture # Materials Used

 

3. BULK TREATMENT PROCEDURES:

Disease/ Treatment] Category Professional Purchase
Condition Procedure Affected Fees Cost

 

211i

MEMS Monthly Disease Report for Operator:
for the Month of
Interview Date: [ [19

1. Disease or Condition:

 

 

Describe:

a Diagnosis made by (check all that apply):
Owner _ Hired Labor _ Manager/operator__ Veterinarian _
NonoVet Professional _ Lab confirmed diagnosis _ Other

 

3. Category Affected: A) Preweaned foals; B) weaned foals: C) growth: D) active; E) inactive adult
(please circle one)

4. Numbersoicases. andcostsincurred:
a) NumberolCasesfromLastMonth:
b) NumberotNewCases: +
c)NumberRecovered: -
d) r-r--rriberwhlch Died ofdisease: - Lossof s_due todeath oianimai(s)

e) Number Sold for this reason: ' - Salvage value: 3 irom saie(s)

 

f) Number Exiting for this reason: -

 

9) Number ot'Cases at End of Month:

5. Treatments Used:

Vet Rx
PIT #

 

6. Professional Fees: $
7. Hours of Labor spent: total hrs

8. Days of animal work lost: tatai days

 

215

MEMS Monthly Equine Financial Inventory for Operator: _ _
tor the Month of .

i. Monthly Income (Total Dollar Amounts)

 

 

 

 

 

 

 

 

 

 

 

 

 

A. Operating Income: 8. Capital Income:
1. Training Fees: __ 1. Sale of Horses:
2. BoardingFees: ___- a. W<2years=
3. Lesson Fees: __ b. Owned > 2years:
4. Breeding Fees: 2. Sales of Equipment:
5. Purses/prize earrings: __ . 3. Sale of Property:
5 Rental fees: equine/propeny: __ 4. Other (specily):
7. Tm'isportlI-Iauling fees:
8. Other Income (specily):
9. Crops Raised: um m m Lin vs

II. Monthly Expenditures (Total Purchases) 10. Hired transport for horses

A. Operating Expenses: 11. Food. imiJodgingexpenses
1. Horse Boarding: 12. Other (specify):
2. Horse Training:
3. Breeding Fees: 8. Capital Expendmires:
4. Registration/EntryFees: 1.a PurchasedHorsesforresale:
5. General Vet consultation: 1.b Purchase not for resale

(not related toaspecificcase) ' 2. Equipment/tack Purchases:
6. Mairuenance and Utilities: . Specily:
7. Insurance/Interefi/Property Tax 3. Propeny Purchases:
8. Labor 4. Other Property improvements:
9. Advertising Specily:
III. Labor hours:
Hired (paid): hrs at § [hr Unpaid Labor. . hrs

N. Monthly 8qu Purchases:

8qu Quantity Purchased On a vet's Total Cost
Purchases Purchased from ' advice?

3. Grain

b.

c.

d.

e.

f. Health related
9. Other

 

' Purchased from yeterinarian. feed/Tack store. glevator. Catalog. or Other

216

CLOSEOUT SURVEY FOR OPERATOR

l. OPERATION INVENTORY

Suvey
Page1ol3

 

I HorsesmdbytheOperatlonasolJan31.1993l . 4?de
I StabiedOFFtheoperation I

II. PERSONNELMANAGEMENT
1. Personsinvolvedwithdailycareolhorses:

TYPE
3. Member: Paid

b. Member:
b. Hired Labor: Pdd
c. Labor:

‘2. Jobdwcrinionotpeoplewonmgregulanyontheoperation:

D I" Average AverageHoursper
Job Number Week Person

 

 

rotuvuuem' I

 

AW Waco
Hour

 

217

P8962d3

III. CHANGES iN FACIUTIES
that have been made In each oithe
oi Morthol

 

Describe

   

aBam
bPMrres/Fences
c.

d.
e.
1.

Facilities
h. Other (describe)

N. CHARGES FOR BOARDING AND TRAINING HORSES:
tryouracatyhdudosaboardngopaatiortcorm. u’nmaidptopatlv.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

FeedmdBedding Maidmum AvgtHorses Isrnaneger
WNW” "M .m 3mm cam ”“23?“ m
PastueOnIy
Pasture/Sn!
StaiIOnly
Other:
2. Training:
A. IstrainingincludedwlthboardNY/N) _
Ifnot.thetrainingieeis s permonth
B. Theeveragenumberoihorsesuainedpermonthlastyearwas __head
3. Lessons:
A Areleesonsincludedwlthboardortraining?(Y/N) _
IInot.theIeesonieeis s perhour

 

B. Theaveragenumberolleseonspermonthlastyearwas more

218

Page3d3

V. IN YOUR OPINION:

1. Corrpaing1992to1991.hawmchdidyouuseyourveterirwianh1992br:(dieckoneloreachtype
olvetserviceused)

Son'rice Morethan'91 NotUsedh‘sz

RoutineCalls
Calls
Conwltation

 

2. Ovenlhowdoyouumkhaseopaafionsuedohgtodayconparedtohstyear’?

Better Same Worse No

Yourhorse
Yourlriends&
The horse
mmmhoteuy

 

3. Whatareyou'lutureplansloryouhcrseoperaion?

 

 

 

 

 

 

 

 

 

 

 

TimeFrame Expand KeepSame Reduce Leevethe OtherPIans:
Operation Size Operation Bus'nees (Deecrbebrielly)
NenYear
NextFiveYeas
4. Whadoyouutiitoltheeflecfimolmese'altemame'therapies?

No Improve Worsen Shouldmoreresearch
Ellect bedoneonthismethod?

C.

d. Laser

9.

r. Other (describe):

 

 

219

Page4ol3

VI. COMMENTS AND SUGGES‘HONS FOR FUTURE MEMS STUDIES:

1. DoyoummamahgmmonamhaseshMidigmwmhebtomprwemeMidingqum
Industrw Y__.N_(check one). Please explain:

 

 

 

2. mmmmmmmmmmem/dem?
Y_.N_ (check one). Pieaseentpiain:

 

 

 

3. Whatdoyouteelwouldbeanhtportemtopictobeemphasizedinmehnurematmayhelpywhorses
ortheequ'ne'ndustryasawhole? Whatmightbeagoodwaytocolectthistypeoliriormation?

 

 

 

4. memmmdmwmammtommwmw

 

 

 

 

APPENDIX B

MICHIGAN EQUINE MONITORING SYSTEM

ROUND 2:

DATA COLLECTION INSTRUMENTS

220

MICHIGAN EQUINE MONITORING SYSTEM PROJECT

Documentation of Reasons for Refusal to Participate in the Project (1992)

MEMSdata collector #__:___
Region of operation: MDC # __ : ___

Size of operation indicated on label: __ (10, 20, 30)
Total number of horses on operation at time ofreftml _;___

Person contacted (state m; of contact, if more than one contacted)
a. Owner

b. Manager
c. Owner/manager

d. Trainer

__ e. Other (specify)

Type of operation (check predominant type)
_ a. Boarding
_ b. Breeding
__ c. Training (me)
_ d. Training (show)
e. Pleasure

_ f. Other (specify)
Predominant breed

 

 

 

State the reasons given by the operator for refusal (please try to give as complete an
answer(s) as possible)

The reasons stated in #7 are those of the operator. What, in my: opinion, were the
reasons for refusal.

u.-

x“ ._..

221

Equine Operator Number

 

MICHIGAN EQUINE MONITORING SYSTEM (MEMS) MUTUAL AGREEMENT

Michigan State University (MSU), the Michigan Department of Agricultrne (MDA), the
United States Department of Agricultm'e (USDA), and the equine Operator hereby enter
intothisAGREEMENT, theterrm ofwhieh are setforthbelow.

1.

MSU, MDA, USDAwillprovidepersonnclwhowillbereferredtoasMEMSDATA
COLLECTOR(MDC). 'l'thDCandtheequineOperatorwillparticipatctogethcr
inhnplemenfingastadsficanyvafidmfordetermnnngesfimatesofmtesand
costs ofequinchealth events.

Theequineopemtorwmmamminadaflydiaryofequmeinventory,healthevents,
andassociatedcosts.

The MDC will complete person-to-perSon interviews with the equine Operator and
collect information from the equine Operator at the monthly visits.

TheequineoperatorwinassistthehflDbeprmddmginformafionregarding
economics,management,anddiseaseconu'ol.-

TheMDCwfllkceptheody’nofthedamgnfiggmjflbyrccordmgthedamfiththe
equineoperator’scodenumberonly. TheMDCwillassignacodenumbertothe
equine operator, but will not keep any key to the code after the data collection
period. With the equine Operator’s consent, theMDCmayconsultwiththe equine
operator's private vetermarian(s) about the health records and associated costs of the
horsesinthe stable.

The MDC will not ask questiom regarding reportable animal diseases. Information
requestcdinMEllrfSwillngtbeusedforregulatoryptn'poses.

MSU, MDA, or USDA may publish, or authorize the publication of by others, the
findings acquired from MEMS for the benefit of the equine industry, private industry,
veterinary medicine, and other interested groups, but will ensure that the identity of
the equine operator is not revealed. '

The MDC will provide the equine operator with a report containing results of data

collected, as well as comparisons to other operators in the state, without revealing the
identity of any equine operators participating in MEMS.

Page 1 of2

 

10.

222

The equine operator will complete an evaluation of the program upon receipt of the
completed report.

The efiective period of this agreement shall be from

 

 

 

 

 

 

month/year
through
- month/year
MEMS Data Collector date
Equine Operator date

Page 2 of2

223

 

OPERATION MANAGEMENT SURVEY FOR OPERATION - : on _I_'_L.

l. Type of Operation

 

In the-following columns, please rank the type of by the money by the hours by the number '
.ICU ' Ines you do on ”'5' operation from 1 up?“ you earn from you spend on .Of horses used
Important) to 12 (least Important). if an actrvrty does the activity the activity ‘0' the acti .
not apply to your Operation, leave the column blank. ”u

A. Boarding .
B. Breeding

 

 

 

Show
C. Training . Race

 

 

 

Hat track
0. Racing Harness

 

 

 

 

E. Work (draft)

F. Lessons

6. Handicappermterapeutic
H. Pleasure

I. Horse sales/Auction barn
J. Riding stable/horse rental
K: Other:

 

 

 

 

 

 

 

 

 

 

 

 

ll. Operation Inventory

 

I ' Please enter the: Number of horses TOtal 83 Value

 

I A. Currently on the Operation

 

 

I 8. Currently of! the operation

 

III. Waste Mahagement

How is manure disposed of? How Often final destination

A. Dumped ant sold)

8. Spread on own land

C. Composted for Own use
0. Sold - not composted

E. Sold - composted first
F. Other:

 

 

224

IV. Professional Services Used

 

 

A. Veterinary Services: On a scale of 1 to 4. how important to your operation are each of the following
' veterinary services? (NIA means that this service is not applicable to your
Operation) ‘
NIA Not important Very import-u
1. Disease Diagnosis 0 1 2 3 4
2. Treatment 0 1 2 3 4
3. Nutritional consultation 0 1 2 3 4
4. Preventive health care 0 1 2 3 4
5. Reproductive work 0 1 2 3 4
6. Source of drugs 0 1 2 3 4
7. Dentistry 0 1 2 3 4
8. Regularly scheduled visits 0 1 2 3 4
9. Physical examinations 0 1 2 3 4
10. Emergencies - O 1 2 3 4
11. Other: 0 1 2 3 4
B. Farrier Services: Onaseale of1 to4, how importanttoyouroperation areeachofthefollowing
farrierservices? INlAmeansthatdtisserviceisnotappiicabletoyour
operation)
NIA Not import-It Very hnportant
1. Outside professional farrier
a. Trimming only 0 1 2 3 4
b. Trim and Shoe ' O 1 2 3 4
e. Shoeing only 0 1 2 3 4
d. Consultation only 0 1 2 3 4
e. Other: 0 1 2 3 4
2. Operation staff (resident)
a. Trimming only 0 1 2 3 4
b. Trim and Shoe O 1 2 3 4
c. Shoeing only 0 1 2 3 4
d. Other: 0 1 2 3 4

 

V. Operation Personnel

Please check (I) to show who is Financial
responsible for the following: Records

. Owner

. Veterinarian

. General manager

. Specialized manager
. Trainer

. Other:

. Not used here

 

 

225

DISEASE MANAGEMENT SURVEY FOR Gammon _L__:__. on _LJ—

l. General Disease Prevention

A. Do horses have to have any of the following before they can enter your operation? Check ll) all that

 

 

 

 

apply:
_ 1. Vaccinations: .
_ 2. Negative uterine culture for broodmares
_ 3. Deworming - type of dewormer:
__ 4. Negative Coggins test
_ 5. Otmr:
B.Doyouisolatehorsesfromtherestoftheherd? Doyouisolatethese? ' Forhowlong?

 

1. Horses retumingfromoutsidetrips li.e. racetrackorshow)

 

2. New horses (new boarder or newly purchasedl

 

3. Broodmaresfrom off'the operation

 

4. Horses with symptoms (high fever, cough, snotty nose. etc.)

 

 

 

 

 

5.0ther:

 

C. How do you keep horses separated during the isolation period? Check (ll all that apply:

 

 

 

 

 

4W.— W
__ 1. Specialbamorbuilding
_ 2. Keptinspacificstall
_ 3. Keptinspecificpaddockorpasture
_ .4. Other:

II. General Disease. Management

A. How do you isolate sick horses? Check (I) all that apply:

_Mmmm_ MW

 

 

 

 

 

__ 1. Special barn or building
_ 2. Kept in specific stall
_ 3. Kept in specific paddock or pasture
_ 4. Other:
8. Do you use any special cleaning procedures for places where sick animals are housed? Y _ N _
If you do.
1. DeSCfibe:

 

2. Disinfectant used (if any):

 

 

226

C. If a horse‘dies.. how do-you dispose of it? Check (I) all that apply:
-1. Bury on the operation

__ 2.‘ Cremate on the operation
_ 3. Hauled away for rendering
__ 4. Sent away for necropsy
_ 5. Composting

_ 6. Other:

 

lll. Disease History

A. Whatarethetopfivehealthproblemsthathaveaffectedyouroperafionoverdiepastfiveyears? Please
listtheminorderfrommostllltoleastlfil important.

 

 

 

 

9'9pr

 

B. What do you think are the top five health problems affecting the entire equine industry? Please list them
inorderfrom most (1ltoleast (5) important.

 

 

 

 

9‘95“!“7‘

 

 

227

Primary Faciity Information for Operator
Interview Date: 1 [

Buid‘ng Information:
1. How many buildings are used to house horses on your operation?
2. Of these buildings.
a. how many are heated?
b. how many have forced air ventilation?
c. how many use natural ventilation (open windows. roof vents. etc.)?
Group Hous'a'lg: i
3. Do you keep horses loose in buildings (indoor group housing)?
4. If you do.

a. How many horses (on average) do you keep this way?

b. What type of flooring is used (i.e. dirt. concrete. wood. rubber mats):

c. What type of bedding is used (i.e. straw. sawdust. sand, etc.):

Page 1

(WM

horses

 

 

d. Feed and Water: Check the appropriate type used (if any)

 

I Loose On Ground Container On Ground Raised Container Other fl

 

I Grains I

 

 

 

 

 

I Forages I

Watering System

Tank
Bucket

Automatic
Waterer

Other

 

Waste Management

1. How frequently are stalls cleaned or 'picked"? __

a. How frequently is bedding changed or stalls “stripped“?

2. How frequently are aisleways swept/cleaned?

3. Where do you dispose of manure?

 

4. Where do you dispose of soiled bedding?

 

 

228

Auxliary Feciity Information for Operator __;__;_
Interview Date: _L__L_

. 1. Describe Auxiliary Am”
F‘Cflifi”: OUIdOOl'S

How Many:

Describe footing:
Dust control used:
Area or dimensions:

Frequency of
maintenance:

 

2. Enter the number of:

Hot walkers: __ Swimming pools:

Treadmills: Round pens:

 

Describe any other training aids you have:

 

Feed and Bedd‘ng Storage:

 

 

 

 

 

 

 

 

 

 

3. Describe how Grain is Stored (I)
in Bags
Indoors Covered
in Containers
Uncovered
in Bags
Outdoors Covered
in Containers
Uncovered
Other:

 

 

 

 

4. Describe how Forages and Bedding are Stored Hay/Forages (I) Bedding (I)

Indoors

Round Bales Covered
Outdoors
Uncovered

Indoors

Covered

Outdoors

Uncovered
Indoors

Outdoors

 

Stall Inventory for Operator 3 :

229

 

Stalls Inside

 

1. Enter Total Number of Stalls:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Din
2 Enter Wood
Number of Concrete
Stalls with
each Type m
0' F'°°""9 Rubber Mats
Other
Straw
3. Enter “St
Number of Wood shavings/chips
Stalls with
each Type Sand
or Bedding Other
No Bedding Used
No Grain Fed in Stall
Loose On Ground
Container On Ground
Grains
4. Enter Raised Container
Number of
Stalls Using om"
these N F F
Feeding o orages ed in Stall
om Loose On Ground
Container On Ground
Forages
Raised Container
Other
Buckets
5- Enter Automatic Waterers
Number of
Stalls Using 0th“
These Water , . .
Optima Water IS heated In wmter time

 

 

No Water In Stall'

 

 

 

 

 

230

MEMS Barn Sheet for Dally Actlvltles on Operation

Horse ID Condition/Situation Costs Income Labor
or # head Hrs

 

 

 

231

RoutineHedthActivity'FonnforOperator_;__;_.formemonthof

 

Activity! Dose!
Treatment Times

Reason Horse ID Given by: Labor Hrs

 

 

‘ Routine Health Activities include things like deworming, vitamin supplements. vaccinations. and
any other health related activities done to prevent disease conditions.

232

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

_O

 

one." s. on...“ \ ounces gnu SEN
I
e be; 2.28: .32.. £8 .3 2.2.3
9.383 .88 8.0 0. etc:
a: N "2.0 3222:. £2.02 tone:
some 3232.0 .2 >653... 95.2

 

233

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

v03
.28..

 

8.28
x

3.9
920

 

:20

 

3.8..

 

3.0
0.3-ecu

82828
25.2.:

 

lasso

 

Sass—o
.338...

 

:3
e25»

 

.8933

 

reoefio

 

 

 

.05.:

 

3.22.3 83:

 

nos—=03.

e20:

 

o. 83:

 

.o 5.32 2: .2.

 

a. 5:230 .6. tone: macaw 2.36m 25:22 9292

 

 

231i

 

6.23:. >238 cc. be... so...“ 63... .2. 3. 2cm ..2. .o tea 6238.. .9. ...M .9238.” "..co :3 8...: ... 23.30 . 5.8.32.5 - .

.....a 9:. 5223.4 ...... cot... ...: .22....ecu .228: 6:35....) .30....” :2... .83: .855 n... 3830 3.25.... .5 3.... 9s) . .

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

..oo .30 on: .30 ..oo eat.
:3 3: ...“. Foe: v.32
:8 8...; 8:35...» 3:30 8:25....» 1:28.35 .9... .3...» :0 >5 3.3.6.3 3180:333 0. ...e:
... JIIJI "8.0 3228:. |£~co2 tone:

g 5:230 .8 :83. 8.8.0 05:5 25:22 252

 

235

Farrier Activities for Operator d__._ for the month of

 

Activity’ 4' feet Who
Cost Mommas

Date Horse ID

(14)

 

 

’ Activity codes are: T for trim only. R for reset shoe without trim. S for new shoe without trim.
TR for trim and reshoe. and TS for trim and new shoe.

’ Code can be F - farrier; V - veterinarian. O - owner/operator. l. - other operation staff

‘ Comments may be used to describe anything unusual here - for example, the application of
pads or bar shoes.

 

235

FarrierActivitiesforOperator _;_;_forthemonthof

 

Activity’ 0‘ feet Cost Who

"°"° '° (1-4) Performed’

 

 

’ Activity codes are: T for trim only, R for reset shoe without trim. s for new shoe without trim.
TR for trim and reshoe. and TS for trim and new shoe.

’ Code can be F - farrier; V - veterinarian. O - owner/operator. L - other operation staff

‘ Comments may be used to describe anything unusual here - for example. the application of
pads or bar shoes.

236

MEMS Breeding Information for Operation

Report Month:

Live Birth

Date Bred Foaling
(if known) Date Filly Colt

 

 

237

MEMS MonthlyDiseaseSummuyfor Operator: __
fortheMonthof
lnterviewDate: _[__;

Disease or Condition:

 

Describe:

 

Diagnosis made by (check all that apply):

Owner_ Hired Labor_ Manager/Operator_ Veterinarian_
Non-Vet Professional_ Lab confirmed diagnosis_ Other

Number of cases, and costs incurred:

a) Number of cases from Last Month:

b) Number of New Cases: +

c) Number Recovered: -

(I) Number which Died of disease: -

e) Number which Died of other disease: -
0 Number Sold for this reason: -

9) Number Sold for other reasons: -

h) Number Exiting for this reason: -

i) Number Exiting for other reasons: -

Lossofe duetoadeath

 

Salvage value: $_ from salels)

i) Number of Cases at End of Month:

Treatments Used:

Professional Treatments
Type # treated Total Cost

 

Professional Fees: 8

 

Hours of Labor spent: __ total hrs

Days of animal work lost: total days

 

 

 

238

Feed‘andBeddingPuchasesforOperator__-_;_forthemonthof

 

HedthRelatedSupples‘Purchasea

 

' NOTE - Feed supplements (vitamins. biotin. antibiotics, etc.) should go on the Health Related Supplies
form below.

Health Related Supplies include things like vitamins. dewormers. vaccines, medicines. first aid supplies
and any other things purchased for equine health.

 

239

MEMS Monthly Equine Financial Inventory for Operator:

for the Month of

Monthly Income (Total Dollar Amounts)

 

 

 

 

 

A. Operating Income: 8. Capital Income:
1. Training Fees: __ 1. Sale of Horses:
2. Boarding Fees: a. Owned < 2 years:
3. Lesson Fees: __ b. Owned > 2 years:
4. Breeding Fees: __ 2. Sales of Equipment:
5. Purses/prize earnings: — 3. Sale of Property:
6. Rental fees: equine/property: __ 4. Other (specify):
7. Transport/Hauling fees:
8. Other Income (specify):
ll. Monthly Expenditures (Total Dollar Amounts)
A. Operating Expenses: B. Capital and Other Expenditures:
1. Horse Boarding: 1.a Purchase of Horses:
’ 2. Horse Training: a. For resale
. 3. Breeding Fees: b. Not for resale
, 4. Registration Fees: 2. Equipment/tack Purchases:
, 5. Showing/Racing Costs: Describe:
(transport. entry fees. lodging. etc.) 3. Property Purchases:
. 6. Advertising/Prometion: 4. Property Improvements:
7. Facility Upkeep: Describe:
(utilities..insurance. etc.) 5. Property taxes
8. Labor and mortgage payments:
. 9. Other (specify):
III. Labor hours:
A. Paid labor:
1. Total number of hours of labor that were paid by the hour: hours
2. Number of laborers that were paid by the month: people
3. Estimate the hours of labor this month that were traded for:
‘ a. Board hours
b. Horse Training hours
c. Lessons hours
d. Other expenses: hours
Describe:

B.

 

Hours of unpaid labor (that was not used to work of services listed above): hours

 

 

240

can... .... .8. be. .88 .o

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

52.. 8c... .95.. E... .26.. was .. cogs .2853... £88.. .581... .53 E28... . ...: .o in... 3556...... .... o. usage... >z< c.2002 3.9. o... .. o
$3.38. .588 .. :2: a... .85.. .. :2: .538... 9.. 3.88.. ...8: b... S 2...: ...... .58.... .3825. 2:28... 5.2. E. b... .29. b... .. ...
«so... o... .. ...... 65...... 6580. .2... E33. ......os .22. b... was 3:... >5... .6: c .....coE 2.. 9...... c... 022...... o... .82 EaE so: a
§§s§u83832.832§5 « «93.852.830.22. .
...0 5.3.0 econ ....0 c.
a... .2...» ......z. ...o ...-.5...» b» as". 3.8.... 53.8.... .88.. .....m .....m 2.8... :3
..E.... e so... a. ...
.520 2:08....» o... 352...... $8.32.. 5...... .....n

 

 

 

 

 

 

 

 

 

 

 

.o ...:oE o... .o. . 3.22.0 .o. no. .20: 3.x mzms.

 

21H

MEMS LAMENESS case FORM for Operation _.-__;_ Page 1
Horse ID: Date form completed: L (

Age: __ years Sex: Breed:

 

 

Part 1 - History of Lameness
1. Is this the first time this horse has experienced this type of lameness?
Y N Don't know

If no, how many previous episodes of this lameness were there? cases

When was the most recent case? ‘ _L_L_ Did the horse fully recover?_(Y/N)
2. Has this horse ever experienced any other types of lameness before this episode?

_Y __N _Don’t know

If yes. when was the last case? __A; Did the horse fully recover?_(Y/N)
Describe the type of lameness:

 

 

Part 2 - Current Case of Lameness
1. Date when lameness was noticed: __L_L_ Recovery date: __[__L
2. How did the horse become lame (if known)?

 

 

3. Who first noticed the lameness?
4. How affected was the horse when the i. neness was first noticed (check ONLY ONE response)?

 

__ Hard to see; not always lame when walking or trotting

__ Hard to see at walk/trot in a straight line. but always in other circumstances (lunge. etc.)
_ Always lame at trot .

_ Obvious lameness: nodding. hitching or shortened stride while walking or trotting.
Favoring legls) when in motion and/or at rest; cannot move comfortably.

5. Who diagnosed this case of lameness (check all that apply)?

 

 

 

 

 

 

Owner Manager __ Hired Labor
Veterinarian Farrier __ Other (describe):
6. What tools were used to aid in clinical diagnosis (check all that apply)?
Visual Examination __ X-Ray Ultrasound -
Joint/Nerve Blocks __ Response to Therapy No clinicaldiagnosis

 

Other (describe):

 

 

242

 

Page 2 MEMS LAMENESS CASE FORM for Operation : ;

Horse ID:

 

7. Describe which parts of the legs and body are affected by the lameness:

Left Foreleg
Hoof
Pastern
Ankle
Cannon

 

 

 

 

Knee

 

Forearm
Elbow
Shoulder

 

 

 

Entire leg

 

Left Hind Leg
Hoof
Pastern
Ankle
Cannon
Hock
Tibia
Stifle
' Thigh
Hip

 

 

 

 

 

 

 

 

 

Entire leg

 

Rest of body (describe):
Head

Right Foreleg

 

 

 

 

 

 

 

 

 

Right Hind Leg

 

 

 

 

 

 

 

 

 

 

 

Neck

 

Back

 

Other

 

 

2143

MEMS LAMENESS CASE FORM for Operation _.;__=_ Page 3
Horse ID:

 

 

When lameness When lameness
occurred was first noticed

8. Describe how the horse

was being worked: 33’0"? gorng lame

 

a. What was the horse
doing?

 

b. How many times a
week?

 

c. Where was the horse
worked (track. arena. etc.)

d. Describe the type of
surface the horse was
worked on:

 

 

 

 

 

 

 

9. How many days of stall rest did the horse get? __ days

10. Outcome:

a. Level of Recovery from lameness as of the end of this report month (check the best response):
_ Complete recovery; back to same condition as before lameness

__ Hard to see; not always lame when walking or trotting

 

Hard to see at walk/trot in a straight line. but always in other circumstances (lunge, etc.)
__ Always lame at trot '

__ Obvious lameness; nodding, hitching or shortened stride while walking.

Favoring Iegls) when in motion and/or at rest; cannot move comfortably.

 

b. Status at the end of this reporting month (check the appropriate response)
Recovered - either totally recovered. or has gotten as well as you expect it will ever get

 

_ Still lame. not recovered Sold or given away because of lameness
_ Put down (euthanize) because of lameness Died due to the lameness

__ Other:

 

 

c. Future of this horse (check the most appropriate response)
Fully recovered, will go back to what it was doing before it became lame

 

Recovered. will do same activity at a lower level than before

 

Recovered. but will be used for other activities
_ Will be left inactive. or be used for breeding purposes only
_ Not yet recovered at end of month

Page 4

Part 3 - Housing and Nutrition
We would like a history of the different housing and feeding methods you have “used on this horse

before it became lame. Describe the housing and feeding methods you were using when the horse
went lame. If you made any changes in the housing and feeding of the horse before the case of
lameness. please record the date you switched the housing and feeding. and what the old housing

and feeding methods were.

21m

 

 

MEMS. LAMENESS CASE FORM for Operation ; :
Horse'lD:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1 . Nutritlo' n:
How was feed provided at If feeding method
a. How is feed provided? the time the horse changed recently.
developed lameness done since _1__L
(check all that apply)
Restricted Free Choice Restricted Free Choice
On Ground
Hay
Off Ground
On Ground
Indoors Grain
Off Ground
Not Heated
Water
Heated
On Ground
Hay
Off Ground
On Ground
Grain
Outdoors Off Ground
Not Heated
Water
Heated
Pasture
b. Describe daily Hay Grain/Pellets Supplements
'at'On-V Type #lday Type r/day Type amt/day
When horse went lame lbs lbs
If ration changed lbs has
recently. since 1 [
Fed at what time of
day?

 

 

 

 

 

 

 

MEMS LAMENESS CASE FORM for Operation _;__:_.
Horse ID:

2. Housing:

 

 

245

 

Page 5

 

How was the horse housed?

Please check all that apply

A. At the time it became
lame:

B. if housing changed
recently.

since _I_L

 

Days Nights

Days Nights

 

Pasture (grass)

 

Outdoors
No Grass

 

Heat

 

No Heat

 

Forced Air Ventilation

 

Natural Ventilation

 

In a stall

Indoors (restricted movement)

 

Loose
(unrestricted movement)

 

Describe type of floor:

 

Describe type of
bedding:

 

 

 

 

 

 

 

 

Part 4 - Comments

 

 

 

 

 

 

 

 

 

 

 

Thank you for your extra time and cooperation!

246

 

 

 

MEMS RESPIRATORY CASE FORM for Operation _;__;_ Page 1
Horse ID: Date form completed: _;L_
Age: years Sex: Breed:

 

Part 1 - History of Respiratory Condition
1. Is this the first time the horse has experienced this type of respiratory condition?
_Y_N_Don't Know
If no. how many previous episodes of this have there been? cases
When was the previous case? _L_L_ Did the horse fully recover?_Y_N
2. Has the horse ever experienced any other types of respiratory problems before?
_Y__N_Don't Know

If yes. when was this case? _L__L__ Did the horse fully recover? _ (YIN)
Describe the type of problem:

 

 

Part 2 - Current Respiratory Condition

1. Date when condition was noticed: _L__L_ Recovery date: __L_L_
2. What seemed to cause the respiratory problem?
3. What clinical signs have been noticed since the beginning of this respiratory condition?

 

 

 

 

 

 

 

 

_a. Runny nose - clear b. Runny nose - cloudy c. Faver

d. Off feed e. Cough - dry f. Cough - congested
_g. Roaring h. Labored breathing i. Wheezing
__i. Blood in nose k. Blood in throat or lungs

 

l. Other (describe)

4. Who first noticed this respiratory problem?

 

5. Who diagnosed this respiratory problem (check all that apply)?
. Hired Labor

 

Owner Manager

Veterinarian Other (describe):

 

6. What tools were used to aid in clinical diagnosis (check all that apply)?
Visual examination __ X-Ray __ Laboratory testing
Endoscope Lung sounds (Stethoscope)

 

Response to therapy

 

 

Necropsy No clinical diagnosis

 

 

Other (describe):

 

 

 

7. What type of respiratory problem is this?

 

247

Page 2 MEMS RESPIRATORY CASE FORM for Operation _:_:_ '
Horse ID:

 

 

8. Describe how the horse

was being worked: Before respiratory When respiratory When problem

problem problem occurred was first noticed

 

a. What was the horse
doing?

 

b. How many times a
week?

 

c. Where was the horse
worked (track. arena. etc.)

d. Describe the type of
surface the horse was
worked on:

 

 

 

 

 

 

 

9. Treatment: How many days of stall rest were given? days‘

 

10. Outcome:
a. Level of Recovery from the respiratory problem at the end of this report month (check the one
best response)
_ Complete recovery; back to same condition as before
__ Recovered. but not back to same condition as before.
__ Not recovered. but doing better

Not recovered. and doing worse

b. Status at the end of this reporting month (check the appropriate response)

 

Recovered - either tetally recovered. or has gotten as well as you expect it ever will

 

Not recovered Sold or given away because of problem
__ Put down (euthanized) because of problem
' Other:

 

Died because of respiratory problem

 

c. Future of this horse (check the most appropriate response)

Fully recovered. will go back to what it was doing before respiratory problems occurred

 

Recovered: will do same activity at a lower level than before

 

__ Recovered: but will be used for ether activities

__ Will be left inactive. or be used for breeding purposes only
Not yet recovered at end of month

 

248

MEMS RESPIRATORY CASE FORM for Operation _L_;__ Page 3
‘ Horse ID:

 

Part 3 - Housing and Nutrition

We would like a history of the different housing and feeding methods you have used on this horse
before it had respiratory problems. Describe the housing and feeding methods you were using
when the horse got sick. If you made any changes in the housing and feeding of the horse MILE
the respiratory problem. please record the date you switched the housing and feeding. and what
the old housing and feeding methods were.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1 . Nutrition:
”m" W“. m" ”mm“ at If feeding method
a. How is feed provided? the time the horse changed recently.
developed respiratory done since 1 I
(check all that apply) problems
Restricted Free Choice Restricted Free Choice

On Ground

Hay
Off Ground
On Ground

Indoors Grain
Off Ground
Not Heated

Water

Heated

On Ground

Hay
Off Ground
On Ground

Grain
Outdoors Off Ground
Not Heated

Water

Heated
Pasture
Hay Grain/Pellets Supplements

 

b. Describe daily rations:
Type #lday Type #lday Type amt/day

 

When respiratory

lb
problem developed ‘ "38

 

If ration changed
recently. since 1 z

Fed at what time of day?

lbs lbs

 

 

 

 

 

 

 

 

 

 

 

 

 

249

Page 4 MEMS RESPIRATORY CASE FORM for Operation .3".
Horse ID:

 

2. Housing:

 

B. If housing changed
recently.
since _[__[__

A. At the time it had
How was the horse housed? respiratory pfoblems

 

Please check all that a l .
pp y Days Nights Days Nights

 

Pasture (grass)

 

Outdoors
No Grass

 

Heat

 

NO Heat

 

Forced Air Ventilation

 

 

Natural Ventilation

 

In a stall
Indoors (restricted movement)

 

Loose
(unrestricted movement)

 

Describe type of floor:

 

Describe type Of
bedding:

 

 

 

 

 

 

 

 

Part 4 - Comments

 

 

 

 

 

 

 

 

 

 

 

Thank you for your extra time and cooperation!

250

MEMS COLIC CASE FORM for Operation ; ;
Date form completed: 1 [

 

Page 1

 

 

Horse ID:

Age: years Sex: Breed:
Part 1 . History of Colic

1. Is this the first time this horse has had colic? _Y

If no. how many previous episodes were there?

_L_L_

Were there any situations that seem to cause colic?

 

When was the most recent case?

cases
How frequently?

_N _Don't know

 

 

2. Symptoms Noticed - check all that applied
_ Off feed
_ Depressed

__ Lying down for long periods
_ Frequent lying down/get up
_ Aggressive _ Pawing/stomping feet
Rolling violently Sweating
Standing stretched

_ Other:

 

Curling upper lip

 

 

Kicking

 

__ Labored breathing
_ Looking at sides
Bloat
. None

 

 

 

3. Describe the colic:

 

Part 2 - Current Case of Colic

1. Date colic began: _L_;
2. What seemed to cause the colic?

Time of day: AM/PM

 

Recovery date: _;_[_L_

 

3. Symptoms Noticed - check all that apply

 

 

 

 

 

 

 

 

 

 

 

 

_ Off feed _ Lying down for long periods Kicking
Depressed _ Frequent lying down/get up __ Labored. breathing
__ Aggressive Pawinglstomping feet __ Looking at sides
Rolling violently __ Sweating __ Bloat
_ Standing stretched Curling upper lip _ None
Other:
4. What type Of colic was it?
5. Who first noticed the colic?
6. Who diagnosed this case of colic (check all that apply)?
Owner __ Manager Hired Labor
Veterinarian Other (describe):
7. What tools were used to aid in clinical diagnosis (check all that apply)?
Visual Examination Rectal Palpation Gum color

 

 

Stethoscope _ Response to Therapy

 

Abdominal Surgery Necropsy

' Other (describe):

 

 

 

 

Abdominal fluid tap
NO clinical diagnosis

 

 

251

Page 2 ‘ MEMS couc CASE FORM for Operation _L..i_.
Horse ID:

 

 

8. What was the clinical diagnosis:

 

When colic When colic was
occurred first noticed

9. Describe how the horse

was being worked: Before colicking

 

a. What was the horse
doing?

 

b. How many times a
week?

 

c. Where was the horse
worked (track. arena. etc.)

d. Describe the type of
surface the horse was
worked on:

 

 

 

 

 

 

 

10. Deworming:
When was the horse last dewormed before developing colic? _/__L_
What type Of dewormer was used?

 

11. Treatment:
a. How many days Of Stall rest did the horse get? __ days

12. Outcome:
a. Level of Recovery from colic as of the end of this report month (check the one best response):

_ Complete recovery; back to same as before Not recovered. but doing better

 

_ Recovered . but not back to same as before Not recovered. and doing worse

 

b. Status at the end of this reporting month (check the appropriate response)
_ Recovered - either totally recovered. or has gotten as well as you expect it will ever get

 

__ Not recovered _ Sold or given away because of colic
_ Put down (euthanized) because Of colic ‘ Died due to the colic
_ Other:

 

c. Future of this horse (check the most appropriate response)
Fully recovered. will go back to what it was doing before it colicked

 

__ Recovered. will do same activity at a lower level than before
_ Recovered. but will be used for other activities

__ Will be left inactive. or be used for breeding purposes only
_ Not yet recovered at end Of the month

252

MEMS COLIC CASE FORM for Operation __L_Z_

Horse ID:

Part 3 - Housing and Nutrition

We would like a history Of the different housing and feeding methods you have used on this horse
before it colicked. Describe the housing and feeding methods you were using when the horse
colicked. If you made any changes in the housing and feeding Of the horse before the case of colic.
please record the date you switched the housing and feeding. and what the old housing and feeding

methods were.

1 . Nutrition:

0

 

Page 3

 

a. How is feed provided?

(check all that apply)

How was feed provided at
the time the horse
developed colic

If feeding method
changed recently.

done since _LL

 

Restricted

Free Choice

Restricted

Free Choice

 

On Ground

 

Hay
Off Ground

 

On Ground

 

Indoors Grain

Off Ground

 

Not Heated

 

Water
Heated

 

On Ground

 

Hay
Off Ground

 

On Ground

 

Grain

Outdoors Off Ground

 

Not Heated

 

Water

 

Heated

 

Pasture '

 

 

 

 

 

 

 

 

b. Describe daily

Hay

Grain/Pellets

Supplements

 

rations: Type

#lday

Type

#lday

Type

amt/day

 

When horse colicked

lbs

 

If ration changed
recently. Since

 

 

 

 

Fed at what time Of
day?

 

 

 

 

 

 

 

253

Page 4 MEMS couc OASE FORM rot Operation _:__:_

Horse ID:

2. Housing:

 

 

A. At the time it colicked:

B. If housing changed

 

 

 

 

 

How was the horse housed? . recently.
Since __[_[_
Please check all that apply .
Days Nights Days Nights
Pasture (grass)
Outdoors
NO Grass
Heat
NO Heat

 

Forced Air Ventilation

 

Natural Ventilation

 

In a stall
Indoors (restricted movement)

 

Loose
(unrestricted movement)

 

Describe type Of floor:

 

Describe type Of
bedding:

 

 

 

 

 

 

 

Part 4 - Comments

 

 

 

 

 

 

 

 

 

 

”tank you for your extra time and cooperation!

 

254

MEMS Recovery Form for Operator __'__;__
for the Month of

Horse ID Condition Change1 Statusz Level Of Activity‘ “mil-:3

 

 

Better since the beginning of the month; 0 = NO change since the beginning of the month: -

1 + =
= Worse since the beginning Of the month

1 R = Recovered: C = Condition continued; D = Died Of condition: P = Put to sleep (euthanized)
because Of condition; S = Sold because Of condition: E = Exit herd because of condition

3 F = Full recovery - back to original condition; P 2 Partial recovery - recovered. but not back to
original condition; N = Not recovered

‘ lf horse was well enough to begin any type of activity. please describe it here.

 

255

CLOSEOUT MANAGEMENT SURVEY for : : . on t (19 Page 1

l. Type of Operatlon

A. In the following columns. please put a check for
anyofactivitiesyoudoonyouroperatiort

Show
Race
Other
Flattrack
Harries

4. Racing
Other:

5. Work

6. Lessons

7. Handicapped/Therapemic

8. Pleasure

9. Horse Sales/Auction Barn

10. Riding Stable/Horse Rental

11. Other -

 

e. WemtilereanymrsesownedbyMeopemimmMemeerMEMShudmemom lltharewere.
1. Howmanyhorseswerethere?
z Howmuch(total)werethesehorsesworth?
What were the major breeds of these horses?

 

4. What were the major activities Of these horses?

 

 

256

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CLOSEOUT MANAGEMENT SURVEY for . on 19 Page 2
II. Changes In Facllltlea
Describe changesthaihavebeen madeineacholthefollowlng:
Type of Facility Month of change Describe
a. Barn
b. Pastures/Fences
c. Stalls/Bedding
d. Watering Systems
a. Feeding Systems
f. Ancillary Facilities
9. Other (describe)
Ill. Charges for Boarding and Tralnlng Horses:
lfyourfacllityincludesaboardingmcontiue. lfnot.skiptOPartN.
memng Maximum A #Horses "mam?"
1'Typedfidmy 3mm Included s/Month Cm gm rem
Pasture Only
Pmre / Stall
Sta" Only
Other.
2. Training:
A. lstrainingincludedwithboard? (YIN) _
lfnot.thetrainingfeeis s _permonth
B. I The average number of horses trained per month last year was _ head
3. Lessons:
A Are lessons included with board or training? (YIN) __
llnot.thelessonfeels S _perhour
B. The average number of lessons per month last year was lessons

257

CLOSEOUT MANAGEMENT SURVEY for : : . on _L__ll.9._ Page 3

IV. Services Utlllzed:

A. Veterinarian: Onascaleofl-4.howlmportantareeachofthefollowlnginthevetennaryse~icesyou
purchase? (N/Ameansnotapplicabletothis Operation). Circlethemebestanswar.

N/A Not Important Very Important
1. Disease diagnosis 0 1 2 3 4
2. Treatment 0 1 2 3 4
3. Nutritional consultation 0 1 2 3 4
4. Preventive heath care 0 1 2 3 4
5. Reproductive work 0 1 2 3 4
6. Source of dmgs 0 1 2 3 4
7. Dentistry 0 1 2 3 4
8. Regularly Scheduled Visits 0 1 2 3 4
9. Physical Examinations 0 1 2 3 4
10. Emergencies 0 1 2 3 4
1 1 . Other: 0 1 2 3 4

B. Farrier: OnasealeOH-4.howinportafla'eeachofmeloflowhginfamerse~icesyoumifize?(NlA
meansnotappllcabletothisoperation). Circletheflbestanswer.

NIA Not Important Very Important

1. Pram (hired)

a. trim only 0 1 2 3 4

b. shoe and trim O 1 2 3 4

c. shoeing only 0 1 2 3 4

d. consultation only 0 1 2 3 4
2 Resident (Operation staff)

a. trim only 0 1 2 3 4

b. shoe and trim 0 1 2 3 4

c. shoeing only 0 1 2 3 4
3. Other (specify): 0 1 2 3 4

 

V. Personnel

A Pleasepmvideadescnpumdpeoplematwempaidforwoddngonyouroperatlon. Useextrapaperilneeded.

 

Number Weeks Average Average
Job Description' - PAID LABORERS oi Warp" Hours per Wage per
workers Week Hour

 

 

 

 

 

 

 

 

 

 

 

 

 

‘ - Job descriptions would describe jobs like trainers. managers. grooms. stall cleaners. etc.

 

CLOSEOUT MANAGEMENT SURVEY for

258

 

-°"_L_£1_9_

Page4

B. PbaseprwideadesaipdondpeopleniawOmOOMwaenapudfawommgmywopMm Plaueuu
extrapaperlfneeded.

Job Description - UNPAID LABORERS

 

Numberof Weehsper AverageHOurs

workers

Year

per Week

'~Jobdesaipdmwmlddesalba]obsflkeuainersnwngus.groam.nafldeametc

1.

VI. In Your Opinion:

YOUI'I'IOISO

Yourfriends&
TheMichiganhorse
Thenatlonalhorse

Better

2 Whatareyourhitureplansforyourhorseoperation?

Same

Worse

No

 

Overan.howdoyouwnkhaseoperalasaredohgtodaycompamdtolaayeafl Checktheonebeaanswer.

 

Time Frame

Expand
Operation

Keep Same
Size

Reduce
Operation

Leavethe

OtherPlans:
(Describebr'iefly)

 

NM Year

 

 

Next Five Years

 

 

 

 

 

 

 

4.

3. Whatdoyoubdievewaemetopmmeheampmuemsmahmoccumdonyomoperadmmlspestyeafl

 

 

 

Whatdoyoubelieveamthetopmmeheanhmemaflectingmeequimindustry?

 

 

 

 

 

 

259

CLOSEOUT MANAGEMENT SURVEY for : : . on I [19 Page 5

Can you suggest ways to improve how information was collected to give a better overview/description Of your
Operation?

 

 

 

Whatdoyoufeelwouldbehnpomarntoplcstobeemphalzedmnnureresearchmamayhelpyowhonesor
theequineindustryasawhole?

 

 

h.-—.- v V. -

 

 

BIBLIOGRAPHY

 

 

BIBLIOGRAPHY

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possible influence of housing systems, management, milk yield. and prior
incidents Of lameness. Prev Vet Med 1996; 29:135—149.

Anonymous. Definition and classification Of lameness. American Association
of Equine Practitioners Guide for Judging of Equestrian Events, 4th ed.
1991 :19.

Barron JK. The effect Of maternal age and parity on the racing performance Of
Thoroughbred horses. Equine Vet J 1995; 27(1):73-75.

Beeman GM. Correlation Of defects in conformation tO pathology in the horse.
Proc Annu Mtg Am Assoc Equine Pract 1973; 19: 1 77-1 98.

Bell LG, Lowe JE. Incidence Of major injuries, severe colic and acute laminitis
at American Horse Shows Association A- and B- rated Shows. JAm Vet
Med Assoc 1986; 188:1304-1306.

Caron JP. Fretz PB, Bailey JV, et al. Proximal interphalangeal arthrodesis in the

horse: A retrospective study and a modified screw technique. Vet Surg
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Cheney JA, Shen, CK, Wheat JD. Relationship Of racetrack surface tO

lameness in the Thoroughbred racehorse. Am J Vet Res 1973;
34(10):1285-1289.

Clanton C, Kobluk C, Robinson RA, et al. Monitoring surface conditions Of a
Thoroughbred racetrack. JAm Assoc Vet Med 1991; 198(4):613-620.

Clarkson MJ, Downham DY, Faull WB, et al. Incidence and prevalence Of
lameness in dairy cattle. Vet Rec 1996; 138:563-567.

Cohen ND, Parson. EM, Seahorn TL, et al. Prevalence and factors associated
with development Of laminitis in horses with duodenitis/proximaljejunitis:
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260

 

261
Collett D. Modelling Binary Data. Chapman and Hall: London. 1991; 369 pp.

Collett D. Mode/ling Survival Data in Medical Research. Chapman and Hall:
London. 1994; 53-105.

Curtis CR, Mauritsen RH. Kass PH, et al. Ordinary versus random-effects
logistic regression for analyzing herd-level calf morbidity and mortality
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Dalin G, DrevemO S, Fredricson I, et al. Ergonomic aspects Of locomotor
asymmetry in Standardbred horses trotting through turns. Acta Vet
Scand 1973; Suppl 44:111-139.

Dolvik NI. Prevalence and risk factors in serous arthritis in the carpal joint Of
Norwegian coldblooded trotters. Vet Res Comm 1994; 18:281-288.

Dolvik NI, Gaustad G. Estimation Of the heritability Of lameness in
standardbred trotters. Vet Rec 1996; 138:540-542.

Dyson S, Wright I, KOId S, et al. Clinical and radiographic features, treatment
and outcome in 15 horses with fracture Of the medial aspect Of the
patella. Equine VetJ 1992; 24(4):264-268.

Eddy RG, Scott CP. Some Observations on the incidence Of lameness in dairy
cattle in Somerset. Vet Rec 1980; 106:140-144.

Estberg L, Gardner IA, Stover SM, et al. Cumulative racing-speed exercise
distance cluster as a risk factor for fatal musculoskeletal injury in
Thoroughbred racehorses in California. Prev Vet Med 1995; 24:253-
263.

Estberg L, Stover SM, Gardner IA, et al. Fatal musculoskeletal injuries incurred
during racing and training in Thoroughbreds. J Am Vet Med Assoc
1996a; 208(1): 92-96.

Estberg L, Stover SM, Gardner IA, et al. High-speed exercise history and
catastrophic racing fracture in Thoroughbreds. Am J Vet Res 1996b;
57(11):1549-1555.

Faye B, Lescourret F. Environmental factors associated with lameness in dairy
cattle. Prev Vet Med 1989; 7:267-287.

Fredericson l. Dalin G, DrevemO S, et al. Ergonomic aspects Of poor racetrack
design. Equine VetJ 1975a; 7(2):63-65.

 

262

Fredericson l, Dalin G, Drevemo S, et al. A biotechnical approach to the
geometric design of racetracks. Equine Vet J 1975b; 7(2):91-96.

Fredericson I, Bergquist A, Bjorne K, et al. Racing on hardwood fiber tracks.
Thoroughbred Rec 1982; 215:501-510.

Gaustad G, Larsen 8. Comparison of polysulphated glycosaminoglycan and
sodium hyaluronate with placebo in treatment of traumatic arthritis in
horses. Equine VetJ 1995; 27(5):356-362.

Groehn JA, Kaneene JB, Foster D. Risk factors associated with lameness in
lactating dairy cattle in Michigan. Prev Vet Med 1992; 14:77-85.

Grondahl AM, Gaustad G, Engeland A. Progression and association with
lameness and racing performance of radiographic changes in the proximal
sesamoid bones of young Standardbred trotters. Equine Vet J 1994;
26(2): 152-155.

Harkins JD, Kamerling, SG. A comparative study of interval and conventional
training methods in thoroughbred racehorses. Equine Vet Sci 1990;
10(1):45-51.

Harman JL, Casella G, Grohn YT. The application of event-time regression
techniques to the study of dairy cow interval-to-conception. Prev Vet
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Harman JL, Grohn YT, Erb HN, et al. Event-time analysis of the effect of 60-
day milk production on the parturition-to-conception interval in dairy
cows. AmerJ Vet Res 1996; 57:634-649.

Harman JL, Grohn YT, Erb HN, et al. Event-time analysis of the effect of
season of parturition, parity, and concurrent disease on parturition-to-
conception interval in dairy cows. AmerJ Vet Res 1996; 57:640-645.

Hill T, Carmichael D, Maylin G, et al. Track condition and racing injuries in
Thoroughbred horses. Cornell Vet 1986; 76:361-379.

Hogan PM, Bramlage LR. Transection of the accessory ligament of the
superficial digital flexor tendon for treatment of tendinitis: long term
results in 61 Standardbred racehorses (1985-1992). Equine VetJ1995;
27(3): 221-226.

Hosmer DW, Lemeshow 8. Applied Logistic Regression. John Wiley: New York.
1989; 307 pp.

 

263

Jeffcott LB, Rossdale PD, Freestone J, et al. An assessment of wastage in

Thoroughbred racing from conception to 4 years of age. Equine Vet J
1982; 14(3): 1 85-1 98.

Johnson BJ, Stover SM, Daft BM, et al. Causes of death in racehorses over a
2-year period. Equine VetJ 1994; 26(4):327-330.

Josseck H, Zenker W, Geyer H. Hoof horn abnormalities in Lipizzaner horses
and the effect of dietary biotin on macroscopic aspects of hoof horn
quality. Equine VetJ 1995; 27(3):175-182.

Kane AJ, Stover SM, Gardner IA, et al. Horseshoe characteristics as possible

risk factors for fatal musculoskeletal injury of Thoroughbred racehorses.
Am J Vet Res 1996; 57(8):1147-1152.

Kaneene JB, Saffell M, Fedewa DJ, et al. The Michigan Equine Monitoring
System. I. Design and Implementation. Prev Vet Med 1997a; 29:263-
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