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LIBRARY
Michigan State
University This is to certify that the
thesis entitled

 

 

THE INFLUENCE OF VARIOUS CONTRATE TO
ROUGHAGE RATIOS ON DIETARY INTAKE AND
NUTRIENT DIGESTIBILITIES OF

presented by

SUSAN KATHLEEN TURCOTT

has been accepted towards fulfillment
of the requirements for the

degree in Animal Science

 

 

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6/01 c1ClRCJDatoDuop65—p. 15

THE INFLUENCE OF VARIOUS CONCENTRATE TO ROUGHAGE RATIOS
ON DIETARY INTAKE AND NUTRIENT DIGESTIBILITIES OF WEANLINGS'

By

Susan Kathleen Turcott

A THESIS

Submitted to
Michigan State University
In partial fulfillment of the requirements

for the degree of

MASTER OF SCIENCE

Animal Science

2003

ABSTRACT

THE INFLUENCE OF VARIOUS CONCENTRATE TO ROUGHAGE RATIOS ON-
DIETARY INTAKE AND NUTRIENT DIGESTIBILITIES OF WEANLINGS

By

Susan Kathleen Turcott

The objective of this study was to compare the feed intake and the apparent
digestibilities of three different diets varying in concentrate to roughage ratios in
weanling horses (n=24) at 5 and 8 months. Horses were stratified by breed, gender, birth
date, and bodyweight and were assigned to one of three dietary treatments containing the
following concentrate to roughage ratios: 70:30 (High Con), 50:50 (Equal), and 30:70
(Low Con). All horses were fed their respective diets for a 10-d adaptation period and a
4-d collection period at 5 and 8 mo of age. There were no differences in body weights or
daily feed intake between treatments with all treatments during both trials (5 and 8 mo)
consuming between 28 and 29 _+_ 1 g/kg BW/d. The horses consuming Low Con had a
greater amount of fecal output than High Con at both 5 mo and 8 mo (P<.01). At 5 mo,
High Con had the highest crude protein digestibility (P<.05). At 8 mo, High Con had a
higher crude protein digestibility than Low Con (P<.01) and a trend to be higher than
Equal (P=.07). Di gestibility of ADP did not differ between treatments; however, horses
fed the Low Con tended to digest a higher percentage of NDF than both the Equal and
High Con treatments (P=0.09). Horses in the High Con treatment tended to digest a
higher percentage of energy than those in the Low Con treatment (P=0.06). Weanlings
seem to digest protein more thoroughly when fed high concentrate diets, and may digest

fiber more efficiently when fed diets higher in fiber.

DEDICATION

I dedicate this thesis to my parents and Tim for understanding my quest for completion '
and supporting my many hours of writing and riding.

iii

ACKNOWLEDGEMENTS

Thank you to my parents, who really thought that horses would be a “passing
phase.” Thank you for supporting me and encouraging me to follow my dreams. The
last two years have been full of challenges: starting graduate school, being diagnosed
with thyroid cancer, undergoing surgery and treatment for thyroid cancer, buying a new
horse, getting engaged, getting married, graduating, accepting a job in Pennsylvania, and
moving across the country. These challenges have helped create the person I am as I
write this, and I expect to be a different person by the time I read this again. Thank you
for teaching me about challenges and change. Your energy is an inspiration to me and

you both have such optimistic views of life and all this it brings.

Tim; thank you for being you. You are patient, caring, hard working, fun, and
absolutely wonderful. I truly appreciate you moving back to be with me, understanding
my many long nights at work, and my need to ride and work with horses. It is exciting to
start our journey together and just know that we will have so much fun in the future:
moving into a new house, running together, training our dogs, trying new sports and
activities, learning to dance, and just spending time together. Thank you for inspiring me

to be a better person and “just relax,” sometimes.

Thank you Cara; your help was instrumental in completion of all my work.
Thank you for going far above and beyond the requirements of work to help me with my
research, equestrian team, and all those little things Ijust must get done. I know there

were times when you dreaded my long phone messages and urgent E-mails, but you

iv

always came through. Thank you for all of your support and friendship. Good luck with
Solo; I will ride him anytime (and try not to get him too “jazzed up”). You will have a
great time teaching the draft horse class and just remember that you know what you know

through hard work and your resourceful nature.

Thank you to my committee for their work in preparing me to succeed at my
defense and learn about research and horse while in school. My graduate program was
perfect for me. I loved the balance of teaching, research, classes, and opportunities to

participate in educational events and extension work.

Thank you to Angie and my other graduate school friends for making me laugh
and realize that I am not the only one struggling through some of the tough times. You
all truly helped me keep my sanity! The best roommate awards go to David Mello and
Katie Swartz. What a fun two years we had. I really didn’t think that things would go as
great as they did. We all balanced each other out so well and you will always be
welcome at the home of Tim and I (even if it is a trailer in the hills). I had a great time at

our “big party.”

Thank you to Dr. Nielsen for giving me the opportunity to get my master’s
degree. I am a different person now than when I started, and am prepared to take on my
dream job. Thank you for always being available, even for my “quick questions” that
often aren’t so quick. I had a wonderful experience and truly value the growth personally

and professionally that I acquired while at Michigan State University.

TABLE OF CONTENTS

LIST OF TABLES .................................................................................. viii

LIST OF ABREVIATIONS ........................................................................ x

INTRODUCTION .................................................................................... 1

CHAPTER 1

LITERATURE REVIEW ........................................................................... 3
Roughages and concentrates ................................................................. 3
Evolution of the horse ....................................................................... 4
Equine digestion .............................................................................. 5
Protein digestion ............................................................................. 6
Carbohydrate and energy digestion ....................................................... 7
Fiber digestion ............................................................................... 7
Weanling digestive system ................................................................. 9
Factors affecting digestion ................................................................ 10
Behavior problems associated with nutrition ........................................... 12
Physiological problems associated with nutrition ...................................... 13
High starch, low fiber diets ............................................................... 15
Feeding weanlin gs ......................................................................... 16

CHAPTER 2

Materials and Methods .............................................................................. 18

CHAPTER 3

Results ................................................................................................ 32

CHAPTER 4

Discussion ............................................................................................ 42

CHAPTER 5

Implications .......................................................................................... 5 1

CHAPTER 6

References ............................................................................................ 53

APPENDIX

Tables ................................................................................................ 59

Equine caecal contents, estimation of total cellulolytic numbers of adult horses. 6.1

VITA .................................................................................................. 83

vi

LIST OF TABLES

Table Title Page

Table 1: Horses used in digestibility studies: horse number, breed, date of birth (DOB),
sex, and treatment .......................................................................... 28

Table 2: Diets fed to Quarter Horses (QH) and Arabians (Arab) prior to starting the
digestibility studies at 5 and 8 mo ....................................................... 29

Table 3: Percentage of ingredients and laboratory analysis of CP, ADF, and NDF for each
treatment diet: High Con, Equal, and Low Con ......................................... 30

Table 4: Calculated nutrient to calorie ratios for CP, Lysine, Ca, and P of the treatment
diets: High Con, Equal, and Low Con .................................................. 31

Table 5: (Mean t SE) body weight, feed intake, water intake, fecal output, frequency of
urination, and frequency of defecation of all weanlings in High Con, Equal, and
Low Con treatments with age, breed, and sex combined ............................. 36

Table 6: (Mean 3 SE) CP, ADF, NDF, and energy apparent digestibility of all weanlings
in High Con, Equal, and Low Con treatments with age, breed, and sex combined
................................................................................................. 37

Table 7: (Mean : SE) body weight, feed intake, water intake, fecal dry matter, fecal
output, and frequency of urination and defecation of horses in High Con, Equal,
and Low Con treatments at 5 and 8 mo ................................................. 38

Table 8: (Mean : SE) CP, ADF, NDF, and energy apparent digestibility of horses in High
Con, Equal, and Low Con treatments at 5 and 8 mo .................................. 39

Table 9: (Mean 1 SE) body weight, feed intake, water intake, fecal dry matter, fecal
output, frequency of urination and defecation, and CP, ADF, NDF, and energy
apparent digestibility of Arabians and Quarter Horses at 5 and 8 mo ............... 40

vii

Table 10: (Mean t SE) body weight, feed intake, water intake, fecal dry matter, fecal
output, frequency of urination and defecation, and CP, ADF, NDF, and energy
apparent digestibility of fillies and colts (Arabs and OH combined) ................ 41

Table 11: Requirements for weanlings at 6 mo expected to reach 500 kg mature BW, but
currently weighing 215 kg and consuming 2.9 % BW/d; NRC recommended diets
compared to High Con, Equal, and Low Con treatment diets ........................ 50

Appendix Table 1A: (Mean t SE) wither height, hip height, and cannon bone
circumference (Cannon C) of Quarter Horses and Arabians at 5 and 8 mo ........ 59

Appendix Table 2A: Average individual feed consumption (g/kg BW/d) of High Con,
Equal, and Low Con by weanlings at 5 and 8 mo during the 10-d adjustment
period ......................................................................................... 59

Appendix Table 3A: Average as—fed calculated values for energy, CP, Ca, and P for

whole oats, protein pellets, Purina Strategy feed, grass pasture, grass hay, and
mixed hay .................................................................................... 60

viii

LIST OF ABBREVIATIONS

ADF — Acid detergent fiber

Arab - Arabian

BW - Body weight as weighed by mechanical scale

Cannon C — Cannon bone circumference

CP— Crude protein

CV — Coefficient of variance

DE - Di gestible energy

DM - Dry matter

Equal — Diet comprised of equal amounts of concentrate and roughage feeds
High Con — Diet comprised of 70% concentrate and 30% roughage
HTRC — Michigan State University Horse Teaching and Research Center
Low Con — Diet comprised of 30% concentrate and 70% roughage

MEC — MSU Merillat Equine Center

MSU — Michigan State University

NDF — Neutral detergent fiber

NRC - National Research Council

SE — Standard error

QH — Quarter Horse

ix

INTRODUCTION

The 1989 NRC recommends feeding a ration consisting of a concentrate to
roughage ratio of 70 to 30. This ratio is based upon the amount of feed that a weanling
will consume due to a small gut size and their limited hindgut development. The limited
development of the caecum and colon in juvenile horses should theoretically result in
decreased digestibility and utilization of the fibrous portion of the diet compared to a
mature animal. The ratio of concentrate to roughage that is consumed is expected to
change throughout the growth period of the horse. In contrast to the high concentrate diet
recommended for weanlings, a diet consisting solely of roughage is recommended for the
non-working, mature equine at maintenance. Both the anatomical and the physiological
makeup of the mature horse’s digestive tract are designed for continual grazing
throughout the day with the majority of the digestion occurring in the hindgut by the
bacteria, protozoa, and fungi microbial inhabitants of the caecum and large intestine

(Gibbs et al., 1988; Julliard et al., 2001).

Though the NRC (1989) recommends a high concentrate diet for weanlings, many
horse owners do not feed this way. A recent study of racehorse farms reported that 98%
of farms fed weanlings diets containing less concentrate than the NRC (1989)
recommended 70% concentrate (Gibbs and Cohen, 2001). Furthermore, 62% of the
farms fed less concentrate than roughage, in sharp contrast to the recommendations of the
1989 NRC. The majority of the horses surveyed (87%) were being fed for moderate

growth, presumably because of a fear regarding the potential for a hi gh-concentrate diet

to maximize, though potentially not “optimize,” growth. Concerns exist over whether
feeding high levels of concentrate may contribute to musculoskeletal problems, behavior I
problems, and increases in management costs. High concentrate diets have been
associated with a variety of musculoskeletal problems, in addition to digestive system
dysfunctions such as laminitis and decreases in caecal and rumen pH values in both

horses and ruminants (Willard et al., 1977).

The question remains as to whether young horses are able to adequately digest
high forage diets to aid in maintaining normal growth rates. Our study begins to answer
these questions in the quest to determine the proper concentrate to forage ratio to be fed

to weanling horses.

The objective of the present study was to compare the feed and water intake and
the apparent digestibilities of three different diets varying in concentrate to roughage
ratios in weanling horses at 5 and 8 mo of age. The hypothesis is that a high concentrate
diet is more thoroughly digested by weanlings compared to a high forage diet, and that

this difference decreases with age.

CHAPTER 1

LITERATURE REVIEW

Roughages and concentratg

Horse feeds can generally be divided into two primary classes of feeds: roughages
and concentrates. Roughages include four main categories of feeds: long and dry hays
and straws, ground and pelleted hay, straw, or oat feed, ensiled long grass and
comparable succulent forages, and chopped succulent ensiled material (Frape, 1998).
Roughages generally contain at least 20 % crude fiber (air-dry basis), and contain high
proportions of cell wall components. Typically, roughages are fed to provide nutrients,
reduce dry matter intake when mixed with other feeds, decrease the net energy intake of
the total diet, maintain an active microbial population in the large intestine and caecum,
and promote equine welfare through decreasing possible diet-associated behavior
problems. Nutrient quality of roughages can vary and depends on type of roughage,

climate effects, soil fertility, and stage of maturity when harvested (Hintz, 1983).

Concentrates are the portion of the horse’s diet comprised of feeds rich in starch,
protein, or both, and typically contain less than 15 to 17 % crude fiber (Frape, 1998).
They are most often fed to increase the energy and nutrient concentration of the total diet
in growing, breeding, or working horses. Cereal grains, milling by-products, and other
formulated supplements are usually referred to as concentrates. Nutrient content and

formulation must be thoroughly investigated when feeding mixed concentrate diets

because the concentrate ingredients in the diet can drastically vary in nutrient

concentrations (Pond, 1995).

Evolution of the horse

There is sizeable variation in management and feeding practices of domestic
horses across the world and throughout history. This is reflective of the many uses for
horses and the availability and costs of suitable environments and feedstuffs. The horse
has developed specific digestive physiology, anatomy, and feeding behaviors associated
with a high fiber diet consumed through grazing and browsing. Prior to domestication,
horses survived on a diet consisting solely of available forages containing relatively large
amounts of water, soluble proteins, lipids, sugars, and structural carbohydrates, but very
little starch (Frape, 1998). Additionally, wild horses consume multiple meals throughout

the day and night during short, frequent feedings.

In domesticated horses, horsemen control the feedstuffs consumed, the frequency
of meals, and the feeding pattern. Domestic horses are commonly fed infrequent, large
meals consisting of starchy cereals, high protein concentrates, and dried forages for
restricted periods of time. Clearly, the art of feeding domestic horses of all classes is to
provide the needed nutrients for service and performance while avoiding digestive and

metabolic upsets resulting from feeding methods and ingredients.

The gastrointestinal tract of the horse is comprised of a small, simple stomach, a
volumetrically limited small intestine, a large caecum, and a sacculated hind gut. This
anatomy allows the horse, a nonruminant herbivore, to digest fibrous diets. However, at
birth the foal is completely dependent on milk for nutrients. The digestive system
changes in the first year to enable the horse to digest starches and eventually fiber. The
age when these changes to the digestive system occur, and the factors that initiate these

changes have not been definitively determined.

Equine digestion

Digestion refers to the preparation of food for absorption, and absorption is the
processes of transporting molecules to the blood system to be metabolized (Pond, 1995).
Digestibility of feedstuffs is evaluated to determine how the digestive system works, how
efficiently an animal retains nutrients, and how effective diet formulations are for
different classes of horses. Digestion coefficients have been developed to measure
efficiency of various feeds (Evans, 1999). Apparent digestibility is calculated according

to the following equation:

Apparent digestibility = 100 x nutrient intake — nutrient in feces
Nutrient intake

True digestibilities are calculated by subtracting the endogenous nutrient sources

from the total amount measured in the feces. However, true digestibility calculations

involve invasive insertion of fistulas and thus they are not determined as often as

apparent digestibilities (Slade et al., 1979).

Protein dgestion

Protein can be found in both the roughage and concentrate portions of the diet. It
is generally accepted that the quality of the protein and its amino acid profile determine
the value of a protein source. The quality of the protein may be more important than the
quantity of protein in the diet. While there is limited information available regarding the
amino acid requirements of horses, it is known that lysine is the first limiting amino acid
(Ott et al., 1981). The lysine content of the total diet has been shown to influence rate of
gain in weanlings and foals even more than the intake of crude protein (Hintz et al., 1971;
Ott et al., 2002; Staniar et al., 1999). Dietary crude protein must be digested and yield

products, amino acids, that can be easily absorbed and utilized.

About 70 % of protein digestion occurs in the stomach and duodenum (Evans et
al., 1999). Interestingly, endogenous fecal nitrogen loss is proportional to bodyweight
and not to the amount of nitrogen consumed, however apparent nitrogen digestibility
increases as the nitrogen content of the diet increases (Slade et al., 1970). Gibbs et al.
(1988) fed three different hay sources to ponies fitted with cannulas in the posterior ileum
to determine true protein digestibility. They found that the large intestine was the major
site for apparent digestion of hay nitrogen, but the role of the small intestine increased as

higher quality hay was fed (Gibbs et al., 1988). Thus, protein from concentrates seems to

be digested more in the upper gastrointestinal tract, while protein from hay sources are

digested mostly in the lower gastrointestinal tract.

Carbohydrate and energy digestion

Carbohydrates are used as energy sources and are present in both roughages and
concentrates. Carbohydrates are molecules composed of carbon, hydrogen, and oxygen.
They include storage carbohydrates, such as sugars and starches, and structural
carbohydrates such as cellulose, hemicellulose, pectins, gums, and lignin (Frape, 1998).
Similar to protein, the soluble storage carbohydrates are primarily digested in the small
intestine, while the insoluble structural carbohydrates are primarily digested in the

caecum and large intestine (Evans et al., 1999).

Carbohydrates are the primary source of energy, but energy can also come from
fats and protein in either roughages or concentrates. The gross energy of a given feed is
the total energy contained in the feed. Upon consumption, energy is either digested or

released as fecal energy.

Fiber digestion
Fiber is the major carbohydrate in equid diets. Starch, cellulose, hemicellulose,
pectin, and sugars make up carbohydrates that vary in digestibility. Fiber is often

measured by determining acid detergent fiber (ADF) and neutral detergent fiber (NDF) to

describe components that are mostly available, incompletely available, and mostly
unavailable (Van Soest, 1975). The NDF portion contains the plant cell wall:
hemicellulose, cellulose, and lignin, while ADF is representative of cellulose and lignin.
The soluble portion of the sample is composed of cell contents and pectin and is made up
of soluble carbohydrates, starch, organic acids, protein, and pectin (Maynard et al., 1979).
Thus, the soluble portions are the most available, while the insoluble portions are

partially available or completely unavailable.

Horses digest relatively the same amount of fiber as mules, donkeys, zebras, and
elephants; yet they digest less fiber than kangaroo, chinchillas, and ruminants (Evans,
1999). Fiber digestion in the horse is directly related to the microbial activity in the
caecum and large intestine for the breakdown of structurally complex carbohydrates.
Bacteria are the most important of the symbiotic organisms and different types of bacteria
are present throughout the digestive tract of the horse. The microbial action forms
primarily acetic, propionic acid, and small. amounts of other acids. The amount of acids
produced per unit dry-matter intake, and their relative proportions, depends directly on
the nature of the feed ration in horses (De Fombelle et al., 2001). Although it is a
common fibrous constituent of most equine diets, Li gnin is most resistant to microbial

attack and indigestible (Evans, 1999).

Cellulose is more easily broken down than 1i gnin, and the hemicelluloses are the
most easily digested fibrous cell wall component. The addition of easily digestible

carbohydrates such as starch, cane sugar or molasses to equine rations may reduce the

digestibility of the fiber. Martin-Rosset and Dulphy (1987) did not find any associative
affects on fiber digestion when varying levels of concentrate were added to a roughage
diet. However, Drogoul et a1. (2001) reported that the fiber digestibility is reduced as the
grain to forage ratio is increased. This is explained by the premise that the bacteria attack
the simpler carbohydrates by preference. It is commonly accepted that bulky
concentrates, those that are high in fiber, are “safer” to feed to horses in high quantities as
compared to concentrates that contain lower levels of fiber and more energy. The equid
has evolved to efficiently utilize a high forage diet, but it is not completely clear at what
stage of maturation the digestive system is developed enough to fully utilize the nutrients

available in high fiber diets.

Weanling digestive system

The equine digestive tract continues to develop from birth through maturity.
During the time after weaning, the large intestine increases in volume faster than the
remainder of the gastro-intestinal tract to accommodate the increased consumption of
fiber in the diet (Frape, 1998). Although the proximal regions, stomach and small
intestine, proportionately grow very little after birth, the distal regions, caecum and large
intestine, continue to grow and develop until the horse is nearly 20 years old (Frape,
1998). Digestion in the caecum and ventral colon depends almost entirely on the activity
and vitality of the rnicroflora of this region. The inoculation and development of fiber-
digesting microflora in the young equid is an area with limited researched data available

at the current time.

Coprophagy in foals is considered normal behavior, but the purpose of its
occurrence is still uncertain. Fransis-Smith and Wood-Gush (1977) have suggested that
coprophagy may serve to introduce bacteria into the foal’s gut and thus supply needed
nutrients, such as vitamins, in which the foal may be deficient. There is either a trend or
direct correlation for foals to consume feces only from their mother (Fransis-Srnith and
Wood—Gush, 1977; Crowell-Davis and Houpt, 1985). However, research seems to
indicate that any coprophagy that supplies foals with nutrients occurs four to six times per
day during the first few weeks of life and thus it would be difficult for the foal to
consume sufficient nutrients that are needed in large quantities (Crowell-Davis and
Houpt, 1985). Furthermore, in rat pups, which also exhibit coprophagy before being
weaned, active ingestion of maternal feces was not necessary for inoculation of the pup’s
gastrointestinal tract with normal flora (Galef, 1979). Coprophagy may serve multiple

purposes in the foal, but inoculation of flora is probably not significant.

Factors affecting digestion

Digestion in the herbivorous animal is a much slower process than in simple-
gutted animals. For instance, pigs pass feed through the gastrointestinal tract in as little
as 24 h (Pond et al., 1995). In horses, it has been reported that 95% of feed particles
consumed pass through the digestive system in 140 h when all roughage diets are
consumed, and 75 h when hay-grain diets are consumed (Maynard et al., 1979; Evans et

al., 1999). This difference in passage rates between the horses is primarily due to the

10

differences in the fiber content resulting from the concentrate to roughage ratio of the

diets studied and the feedstuffs fed.

The processing of feeds is a common practice in the equine industry presumably
to increase the digestibility of the feeds. Although pelleted feeds are often more
expensive because of additional processing, they are easier to weigh, feed, store, and
transport (Earle, 1950). Concentrates are often processed into pellets of mixed
ingredients, though complete diets consisting of concentrate and roughage combined are
also fed in the industry. Wolter et al. (1974) found that digesta of horses consuming
ground hay passed more quickly through the digestive system than long-stem hay, and
the horses showed decreased digestibility of nutrients. Pelleting presses ground hay into
pellets and similarly decreases digestibility by increasing the rate of passage through the
digestive system (Cympaluk and Christensen, 1986). However, pelleting of concentrated
and concentrate-hay diets has been reported to either increase digestibility of the
ingredients or not change the digestibility when compared to the same diet in an

unpelleted form (Frape, 1998, Hintz et al., 1972, Hintz et al., 1966).

Feed intake is regulated by intragastric regulators that monitor distension of the
stomach, presence of soluble carbohydrates, rate of gastric emptying, and the osmolar
concentration of infused or ingested solutions (Ralston et al., 1982). The mechanisms
controlling appetite in horses are still unclear. Equine satiety regulators are different than
the mechanism in ruminants, which are more directly related to the classical factors such

as crude protein and crude fiber contents (Faverdin et al., 1995). Horses are not able to

11

regulate appetite by sensitive physical appetite-regulating mechanisms (Ralston and
Baile, 1982; Laut et al., 1985). Ralston and Baile (1982) suggest that there are four main ‘
stimuli which may be responsible for the generation of cues in the gastrointestinal system
that determine feeding behavior: distension of the stomach or proximal gut or both,
presence of soluble carbohydrates or other nutrients in the proximal gastrointestinal tract,
the rate of gastric emptying (may be dependent on upon nutrient concentrations and
volume of gastric contents), and the osmolar concentration of infused or ingested

solutions.

Increasing the frequency of feeding meals and large feed intakes consumed at a
rapid rate will increase the rate of passage of ingesta through the digestive system, and
slightly reduce roughage digestibility (Pearson and Merritt, 1991). Interestingly, light
exercise improves digestibility, while heavy work decreases digestibility (Olsson and
Ruudevere, 1955). However, individuality also is an important factor when studying
digestibility. Fonnesbeck et al. (1968) found differences in the ability of mature horses to
digest protein even when consuming the same diets. Time of feeding and watering may

also influence digestibility in horses.

Bejgrvior problems associated with nutrition
Diets high in concentrate and low in forage offer a variety of possible welfare
concerns. Two important concerns pertinent to weanlings are gastric ulcers and oral

behavioral stereotypies. There is a high prevalence of gastrointestinal ulcers found in

12

foals. Reportedly up to 51% of foals fed high concentrate -— low fiber diets show some
gastric lesions (Murray, 1989). Oral stereotypies such as crib-biting and wood-chewing '
in adult horses have been associated with high concentrate and low forage diets
(McGreevy et al., 1995; Willard et al., 1977). Nicol et al. (2001) found cribcbiting in
foals to be associated with gastric inflammation and ulceration. Furthermore, it has been
suggested that wood chewing may result from low fiber diets (Naenlein, 1969), boredom
(Ralston et al., 1979), or malnutrition (Schurg et al., 1978). Clearly nutrition and feeding
management are directly related to behavior welfare, but additional research is needed in
this area to determine the best feeds and methods of feeding for weanling horses of

varying uses.

Physiological problems agociated with nutrition

Limiting nutrients in young, growing horses can be detrimental to both quantity
and quality of growth. It is commonly agreed that for maximum growth rates, roughage
or pasture must be supplemented with concentrates. Dawson et al. (1945) found a
delayed maturity and stunted skeletal development in horses fed only Western range
forages from birth through three years of age. Similarly, foals fed a diet containing 9%
protein from 120 d of age to 260 (1 showed very low average daily gain, low average
daily feed intake, high feed to gain ratio, and decreased height and cannon bone
circumference compared to young horses fed diets consisting of 14 and 20% protein
(Schryver et al., 1986). Protein values below the NRC recommendations cause decrease

growth parameters (average daily gain, wither height, hip height, cannon bone

13

circumference), but levels fed above the NRC requirements have not shown any
differences in growth if energy and other nutrients are sufficient (Schryver et al., 1986).
Although excess protein can be used for energy, non-protein nitrogen such as urea can be

lethal if fed at high levels (Hintz et al., 1970).

Underfeeding the weanling may result in problems associated with mineral and
vitamin deficiencies (Hintz, 1996). Furthermore, energy deficiency in weanlings results
in a slow rate of growth and a general unthrifty appearance (Ellis and Lawrence, 1979).
Feeding restrictions may also delay closure time of the epiphyseal cartilage of proximal
and intermediate phalanges and third metacarpus (Ellis and Lawrence, 1978; Rezende et
al., 2000). However, 6-mo-old horses, malnourished for 4 mo, can recover when fed
properly through compensatory gains (Ellis and Lawrence, 1979). The young horses
reportedly were able to attain body weights and heights similar to the horses fed adequate
levels of energy and protein. It is unclear what, if any, long-term problems may be

associated with early malnutrition.

In addition to obesity, overfeeding energy may result in problems associated with
the integrity of growth. Overfeeding young, growing horses can lead to horses that may
appear healthy, but develop severe problems from excess strain on their developing
frames. Weanlings that grow and mature quickly are often prized in the equine industry
because of the possibility of beginning training and competitive careers at a younger age.
The growth potential is further embellished by feeding high concentrate diets with high

concentrations of energy.

14

A high nutritional plane and rapid growth have been associated with
developmental orthopedic diseases (Hintz and Kallfelz, 1981; Wright and Pickles, 1991).
Ideally, growth of a foal should follow a smooth curve, being steepest in the first few
months of age and gradually leveling out after about 2 years of age (NRC, 1989). Most
breeds today reach about 90% of their mature body weight by 18 mo of age (Frape,
1986). Jelen et al. (1996) describes growth from birth to 20 mo in four phases: birth to 1,
l to 12, 12 to 15, and 15 to 20 mo. Since the average daily gain changes during each
phase of growth, this may be especially important when formulating diets for growing

equines.

High starchJow fiber diets

High starch, low fiber diets are associated with rapid growth and often increased
weight gain and strain on the growing bone structure. Diets high in starch cause changes
in serum insulin, thyroxine, and triiodothyronine, which slow cartilage maturation (Glade
and Belling, 1984; Glade and Luba, 1987). Rezend et al. (2000) found foals
supplemented with a concentrate mix prior to weaning until 12 mo had lower frequency
of epiphyseal cartilage alterations and better cortical index when compared to foals not
receiving the concentrate mix until after weaning. This is presumably because of
mineral deficiencies and their association with epiphysitis. Interestingly, the amount of
concentrate in the diets of the weanlings from weanling until 12 mo was still comprised

of less than 70% concentrate in the total diet.

15

There may also be a link between above-average weight gains and the onset of
epiphysistis and other related disorders (Thompson et al., 1987). The increased force on
the bone structure from the heavy body weights may impair normal cartilage and bone
development. An 8-year study in dogs found that maintaining body condition scores of
dogs at or slightly below what is currently considered to be optimal had decreased
incidence of degenerative joint disease throughout the lives of the dogs (Smith et al.,
2001). Developmental orthopedic disorders in horses can have huge economic
repercussions in the horse industry such as lower sale prices of young horses and

decreased performance potential (Thatcher, 1991).

Feeding weanlings

The optimal growth rate for horses to produce maximal soundness and future
performance remains unclear. The NRC (1989) is the most frequently used compiling of
equine nutritional research and associated recommendations for feeding classes of horses.
Producers feeding weanlings can feed for either moderate or fast growth with the primary
difference between diets being the level of energy intake. A weanling that is expected to
reach a 500 kg mature weight should consume 15 Mcal DE, 750 g crude protein, 29 g
calcium, and 16 g phosphorous daily to meet the requirements if being fed for moderate
growth. On the other hand, a weanling that is being fed for fast growth is expected to
consume 17.2 Meal DE, 860 g crude protein, 36 g calcium, and 20 g phosphorous.

Feeding these values will have a daily expected gain of 0.65 and 0.85 kg/d, respectively.

16

The expected feed consumption per day for weanlings is 2.0 to 3.5% body weight with
recommendations of 0.5 to 1% BW consumed as forage and 1.5 to 3% BW consumed as ’
concentrate (NRC, 1989). These values were created as guides for managers, but factors
such as processing of feeds, level of intake, disease, previous nutritional status, work, and
individuality can have an affect on the individual equine to increase or decrease these

requirements.

More recently, Ott et al. (2002) provided evidence that the NRC (1989) values for
dry matter intake for weanling horses are 4 to 13% too high and the DE requirements are
4 to 12% too high. The protein requirements may also be 2 to 20% in excess of the actual
needs of weanlings (Ott et al., 2002). Monitoring intake and determining digestion of
different feedstuffs in weanling horses will aid in the determination of more specific
recommendations for feeding weanlings for growth which promotes healthy, functional

horses.

17

CHAPTER 2

MATERIALS AND METHODS

Animals and Management

Twenty-four horses (12 Quarter Horses and 12 Arabians) at 5 mo of age and again
at 8 mo of age (1 Quarter Horse was no longer available) were used to study the
digestibility of three diets. Arabians (Arabs) and Quarter Horses (QH) were obtained
from and housed at the Michigan State University Horse Teaching and Research Center
(HTRC) and the MSU Merillat Equine Center (MEC), respectively. Digestibility studies
consisted of a 10-d pre-trial adjustment period followed by a 4-d total fecal collection.
The study was approved by the Michigan State University Animal Care and Use

Committee (05/02-018-00).

Weanlings were stratified by breed, date of birth, and gender to avoid
confounding factors previously identified by Heusner (1992) and Hintz et al. (1979) and
were randomly assigned to one of three treatments (Table 1). Weanlings were age-
matched in four groups of five to seven horses, such that each group entered the study at

a mean age of 5 mo :16 (1.

Before the start of the digestibility studies, both QH and Arabs were group-fed

and group-housed in mixed grass pastures with free access to water, rnineralized salt

blocks, and shelter. Prior to the start of the 5 mo digestibility study, all QH (n=12) were

18

consuming approximately 3.77 kg commercial concentrate mix (Strategy; Purina Mills
Inc., St. Louis, MO) and 2 kg alfalfa-grass mixed hay (Table 2). Before the 8 mo
digestibility study, all QH (n=1 1) were consuming approximately 2 kg commercial
concentrate mix (Strategy; Purina Mills Inc., St. Louis, MO), 3 kg mixed grass pasture,
and 2.5 kg grass hay (Table 2). Arabs (n=12 throughout) at both 5 and 8 mo were
consuming free choice mixed grass hay, whole oats, and protein pellets in addition to the

mixed grass pastures available (Table 2).

At the start of both digestibility trials, weanlings were separated into treatment
groups and moved into dry-lots for a 10-d adjustment period. This period allowed for the
elimination of any feed eaten prior to the start of the 4-d fecal collection period and let
the weanlings become accustomed to the feeds and feeding methods used in the study.
Quarter horses were moved into 992 to 1,488 m2 dry-lots with one to three horses per lot,
while Arabians were moved into 4,046 to 6,070 m2 dry-lots with two horses per lot.
During this time, all horses had free access to water, mineralized salt blocks, shelter, and
their respective treatment diet. Metal, three-sided sheds with dirt flooring were provided
for shelter. Feed was placed into large rubber feed tubs located inside the sheds. Horses
and feed were checked twice daily and a minimum of 12 kg feed was maintained in each

tub to assure free access to feed.
Following the adjustment period, horses were moved into individual stalls for a 4-

d fecal collection period. Quarter Horses were moved to 3.7 x 3.7 m stalls at MEC while

Arabians were moved into 4.0 x 3.4 m stalls at HTRC. All stalls were swept, vacuumed,

l9

and completely lined with clean rubber mats to remove dirt and debris. Stalls were also
hand-swept a minimum of three times each day during the 4-d collection. All horses had '
free access to water, feed, and a mineralized salt block. Water was provided in 19 l
buckets filled 1/2 to 3%: full, while feed and the mineralized salt block were placed in plastic

feeders mounted in the stalls.

Treatments

The treatment diets were custom-formulated, mixed, and pelleted for this research
project by Hamilton Feeds (Hamilton, MI). Complete diet pellets (3.18 mm diameter) for
each treatment diet were prepared for the entire project in three respective batches. The
diets consisted of concentrate and roughage in the following ratios: 70:30 (High Con);
50:50 (Equal); 30:70 (Low Con). The roughage portion of each diet contained an equal
amount of alfalfa hay and timothy grass hay acquired from the same source for all diets.
The concentrate portion of the diets was formulated using primarily corn, soybean meal
and oats to best represent feeds commonly used in the industry (Table 3). Each treatment
diet was nutritionally balanced to meet the NRC (1989) requirements for weanlings.
Diets were not isonitrogenous or isocaloric; however, nutrient to calorie ratios of Mcal,

CP, lysine, Ca, and P to DB were constant across treatments (Table 4).

20

Mmmrents and Sample Collection

Horses were weighed on a digital scale at the start of the adjustment period and at.
the start and end of the collection period. Wither height, hip height, and cannon bone
circumference were also measured at the end of the collection period, as indicators of the
size of the horses at different ages and locations (Appendix Table 1A). Feed
consumption during the adjustment period was calculated by subtracting the total weight

of the orts from that of the total feed given over the 10-d period (Appendix Table 2A).

Horses were monitored continuously throughout the 4-d (96 h) fecal collection
and stalls were checked at least every 15 min. Each 24-h period began at 0900.
The time of each defecation and urination was recorded for each horse. Urine was
removed from stalls via a commercial wet-dry vacuum to avoid contamination of feces.
Fecal matter was immediately collected from the stall floor with a treatment specific
plastic dustpan and rubber gloves, weighed on a digital scale to the nearest 0.01 kg, and
placed in an airtight labeled plastic bag on ice in a cooler. At the end of each 24-h
period, fecal material collected from each horse was thoroughly hand-mixed and a 1 kg

sample was retrieved and frozen in a commercial freezer (below -4°C) for future analysis.

During the 4-d fecal collection period, feed, a mineralized salt block, and water
were provided free choice as in the 10-d adjustment period. Water consumption was
gravimetrically measured every 8 h. Feed or water were removed from the stall for
weighing a maximum of 15 min to limit the time horses did not have access to them. At

the start of the 4-d collection period, horses were fed their respective treatment diets in

21

amounts equal to 3.5% of their body weight (BW). Daily feed intake was determined at
the end of each 24 h and each horse was then fed 5% more feed than they had consumed ’
on the previous day to ensure that feed was not restricted. Feed buckets in each stall were
checked when fecal matter was collected or urine was removed. If a horse had consumed
all of the feed presented, such that only feed particles (no full pellets) remained in the

feeder before 0900, more feed was added in 1 kg increments.

Laboratory Analyses
Sample preparation and dry matter

Feed samples were ground in a Wiley mill and passed through a 2 mm screen and
fecal samples were ground in a Cyclone mill and passed through a 1 mm screen. Feed
samples from each sample period were analyzed on an as fed-basis, while fecal samples
were individually freeze dried prior to grinding. Initial analysis showed no difference in
nutrient analysis between fecal samples collected each day during the fecal collection
period, thereafter (1 3 and 4 fecal samples were combined for each horse by taking sub-
samples from d 3 and 4 in equal proportions to the total amount of fecal matter defecated '
(total g DM) each day. All samples were analyzed in duplicate. Values were averaged
and coefficient of variance (CV) was accepted at less than 5%, 2%, 2%, and 5% for CP,
ADF, NDF, and energy, respectively. If CV was greater than the accepted rate, two
additional samples were analyzed, then the highest and lowest values were dropped and
the two remaining values were averaged to obtain a new CV. This process was repeated

until the CV was at an acceptable level for the given measurement. Dry matter (DM)

22

values for all feed and fecal samples during each trial were determined by drying 2.5 to

3.0 g samples in a laboratory oven at 105°C for 24 h.

Crude protein

Crude protein of feed and fecal samples were determined by a non-dispersive,
infrared, microcomputer based machine, designed to measure nitrogen content in samples
(LECO® FP-2000 Nitrogen/Protein Analyzer). Samples were weighed (0.4 to 0.5 g) and
placed in a ceramic boat prior to being placed into the machine. The machine combusted
each sample by pushing samples into a combustion chamber filled with oxygen gas and
thus converting elemental nitrogen into NOx gasses. This gas entered a series of
chambers for cooling before two gases (Lecosorb® and anhydrone) were released to
remove C02 and H20, respectively, leaving N2 and helium. The gasses were then
measured and compared to determine a voltage which was then processed and given as a
nitrogen measurement by the computer. The ceramic boats were later removed from the
machine and cleaned. Nitrogen content was automatically calculated to CP values by the

machine.

23

Fiber
Wet chemistry processes were used to determine ADF and NDF of the samples.

ADF was determined as a fraction of dry matter (Goering and Van Soest, 1970).

ADF (g) = (crucible gnd ADF residue weight) — (crucible and ash residue weight)
g of sample dry matter

Samples (0.5 and 1.0 g for fecal and feed, respectively) were placed into 600 ml
Berzelius beakers. Acid-detergent solution (100 ml) was then added prior to beakers
being set on a refluxing apparatus and heated to boiling for 60 min. Beaker contents
were then poured into crucibles containing 5 ml sand that were! vacuumed and rinsed with
hot (90 to 100°C) water. Each crucible was then washed with acetone and allowed to air
dry before being placed in a laboratory oven (100°C) for 8 h. Crucibles were hot
weighed before they were ignited in a muffle oven kept at 500°C for 5 h. After cooling to

100°C, crucibles were again hot weighed.

Similarly, NDF was determined as a fraction of dry matter (Goering and

VanSoest, 1970; Robertson and VanSoest, 1977; Chemey et al., 1989).

NDF (g) = (crucible and NDF residue weight) — (crucible and ash residue weight)
g of sample dry matter

 

Samples (0530.01 g) were placed into 600 ml Berzelius beakers. Sodium sulfite

(0.5 g), neutral-detergent solution (100 ml), and heat stable amylase (2 ml) were then

24

added prior to beakers being set on a refluxing apparatus and heated to boiling for 60
min. Two ml of working amylase was added to each beaker after being removed from
the refluxing apparatus. Beaker contents were then poured into crucibles containing 5 ml
sand that were vacuumed and rinsed with hot (90 to 100°C) water. Each crucible was
then washed with acetone and allowed to air dry before placing crucibles in a laboratory
oven (100°C) for 8 h and then hot weighed. Crucibles were then ignited in a muffle oven

kept at 500°C for 5 h. After cooling to 100°C, crucibles were hot weighed.

Energy

An oxygen bomb calorimeter (Parr Instrument Company Inc., Moline, II.) was
used to determine the energy content of feed and fecal samples. Wiley milled samples
were pressed into pellets (0.7 to 1.1 g for fecal and 0.9 to 1.1 g for feed) and weighed just
prior to loading into the bomb calorimeter. Bensoic acid, the standard, was analyzed
before the first sample and each time a group of samples were analyzed more than one
week apart. Samples were loaded into the combustion capsule with a 10 cm fuse wire in
contact with the sample loaded into the bomb head. Capsules were then filled with

oxygen to 32 atm.

The combustion capsule was placed in a calorimeter bucket filled with 2,000 ml
distilled water and placed into the calorimeter. Two ignition wires were attached to the
terminal sockets on the bomb head, the calorimeter was covered, and an initial

temperature was taken. At least 6 min after igniting the calorimeter, the temperature was

25

taken. The unburned pieces of fuse wire were removed from the bomb electrodes,
straightened, and the length measured. The energy equivalent of the bombs A and B

were 2,400 and 2,398 cal/°C, respectively.

Heat of combustion (cal/g) = tW — (cglories of wire burned)
g of pellet sample

t = temperature final — temperature initial
W = energy equivalent of the bomb used

Apparent Digestibility
Apparent digestibility of CP, ADF, NDF, and energy was calculated by the
following equations on a DM basis:
CP, ADF, or NDF Digestibility (%) = g in feed - g in feces x (100)
g in feed

g in feed = g consumed/d * (% nutrient in feed sample)
g in feces = g defecated/d * (% nutrient in feces sample)

Energy digestibility (%) = Mcal energy in feed - Mcal energy in feces x (100)
Mcal energy in feed

Digestible Energy (Meal/kg) = Mcal energy in feed — Mcal energyin feces + (BW)
Mcal energy in feed

Mcal energy digested = Mcal energy in feed — Mcal energy in feces

Energy in feed = Mcal consumed/d * (% energy in feed samples)
Energy in feces = Mcal defecated/d * (% energy in fecal samples)

26

Misticgl Analyses

Significance of differences between means were determined for treatments, age,
breed, sex, treatments within age, and breeds within age were determined using PROC
MIXED (SAS, 2001). A repeated-measure design was used with treatment, breed, and
sex as the main effects and time as the repeated effect. The LSMEANS test was used to
compare means. A P-value of less than 0.05 was considered significant, and a P-value of

less than 0.10 was considered a trend.

27

Table 1: Horses used in digestibility studies: horse number, breed, date of birth (DOB),
sex, and treatment

 

 

Horse Number Breed DOB Sex Treatment
1 OH 1/19/02 Colt Low Corr
2 QH 1/30/02 Colt Equal
3 OH 2/2/02 Filly Low Con
4 QH 2/23/02 Colt High Con
5 OH 2/23/02 Filly High Con
6 QH 2/25/02 Filly Equal
7 QH 3/3/02 Colt High Con
8 OH 3/20/02 Colt Equal
9 QH 3/26/02 Filly Low Con
10 QH 4/3/02 Filly Low Con
11 OH 4/10/02 Colt High Con
12* OH 4/20/02 Colt Equal
13 Arab 3/31/02 Colt Equal
14 Arab 4/2/02 Filly High Con
15 Arab 4/5/02 Colt High Con
16 Arab 4/8/02 Colt Equal
17 Arab 4/19/02 Filly Low Con
18 Arab 4/19/02 Filly Low Con
19 Arab 5/9/02 Filly Equal
20 Arab 5/13/02 Filly Equal
21 Arab 5/ 14/02 Filly Low Con
22 Arab 5/18/02 Colt Low Con
23 Arab 5/21/02 Colt High Con
24 Arab 5/23/02 Filly High Con

 

* Horse not available, therefore not used in 8 mo digestibility study

28

Table 2: Diets fed to Quarter Horses (QH) and Arabians (Arab) prior to starting the
digestibility studies at 5 and 8 mo.

 

 

Feed Ingredient 1%) OH, 5 mo 0H, 8 mo Arabs, 5 mo Arabs, 8 mo
Concentrate

Whole Oats - - 45 30

Protein Pellet - - 10 10

Purina Strategy 65 20 - -
Roughage

Grass Pasture - 40 45 5

Grass Hay - 30 - 50

Mixed Hay* 35 - - -

 

* Mixed refers to grass and alfalfa mix

29

Table 3: Percentage of ingredients and laboratory analysis of CP, ADF, and NDF
for each treatment diet, High Con, Equal, and Low Con

 

 

 

Ingredients (%) High Con Equal Low Con
Corn 19.00 30.00 29.15
Oats 43.00 14.60 0.00
Soybean Meal 6.00 4.00 0.00
50:50 Hay Mix 30.00 50.00 70.00
Lysine 0.09 0.15 0.23
Buckeye® Vit/Min 0.15 0.15 0.15
Salt 0.06 0.05 0.08
Dicalcium Phosphate 0.55 0.55 0.00
Limestone 1.15 0.45 0.00
Phosphate 0.00 0.05 0.40
Nutrients 1 % )
CP 14.001020 15.001020 12.801020
ADF 16.401060 17.501060 22.901060
NDF 29.801040 29.201040 35.401040

 

30

Table 4: Calculated nutrient to calorie ratios for CP, Lysine, Ca, and P of the treatment

diets: High Con, Equal, and Low Con

 

 

Measurements High Con Equal Low Con
g CP/ DE Mcal 51.9 52.0 52.0
g Lysine/ DE Mcal 2.2 2.3 2.2
gCa/ DE Mcal 3.1 3.1 3.1
g P/ DE Mcal 1.5 1.5 1.5

 

31

CHAPTER 3

RESULTS

Iggatment effects (game, breed,2_tnd sex combined)

Body weight, feed intake, and water intake were not different (P=0.89, P=0.96,
and P=0.37, respectively) between treatments when age, breed, and sex were combined
(Table 5). However, fecal DM was greater in the High Con group compared to the Equal
and Low Con groups (P<0.05). There was a trend of greater fecal output by the
weanlings consuming the Low Con diet compared to those consuming the High Con diet
(P=0.09). Although the number of times per day horses urinated was not related to
treatment, the frequency of defecation was related to treatment (P<0.01); horses in the
Low Con treatment defecated more often than those consuming High Con and Equal

diets (Table 5).

Crude protein apparent digestibility was affected by treatment (P<0.01), with
horses consuming the High Con digesting more protein than those consuming Low Con
(Table 6). Apparent digestibility of ADF did not differ between treatments with values of
32.6 :t 2.9%, 33.3 i 2.9%, and 39.7 t 3.0% for High Con, Equal, and Low Con,
respectively (P=0.21; Table 6). However, horses fed the Low Con tended to digest a
higher percentage of NDF than both the Equal and High Con treatments (P=0.09; Table
6). Horses in the High Con treatment tended to digest a higher percentage of energy than

those in the Low Con treatment (P=0.06; Table 6).

32

Age effects (breed and sex combined)

The body weight of weanlings increased from 5 mo to 8 mo (P<0.01; Table 7).
There were no differences in body weight among treatments (P=0.97), with an average
body weight for all weanlings at 5 and 8 mo of 200 z 4 kg and 259 -_t- 4 kg, respectively.
Feed intake was the same across treatments and ages, but weanlings drank more water at
5 mo than 8 mo (P<0.01). When treatments were combined, feces from weanlings at 5
mo contained a higher fecal dry matter, although there were no differences in fecal
output. Weanlings urinated and defecated more frequently at 5 mo than 8 mo, regardless
of treatment (P<0.05; Table 7). At 8 mo, there was a trend for the horses consuming High

Con to urinate more frequently than horses consuming Equal and Low Con diets.

Weanlings fed the Low Con diets digested more CP at 5 mo than at 8 mo (P<0.05;
Table 8). Weanlings at 5 mo fed High Con digested more protein than those fed Equal
and Low Con diets. Similarly, weanlings at 8 mo fed the High Con diet digested more
CP than the Low Con diet. In contrast to CP, the apparent digestibility of ADP, NDF,

and energy did not differ with age when treatments were compared.

Breed effects (treatment and sex combined)
The body weight of QH was 10% and 23% greater than Arabs at 5 and 8 mo,
respectively (Table 9). At 5 mo, the Arabs consumed more than the QH, while at 8 mo

the OH consumed more than the Arabs. Water intake was similar in Arabs and OH at 5

33

and 8 mo. In Arabs, percent fecal dry matter was higher (27.0:0.4%) than in OH
(24.7:0.4%; P<0.01). Although the Arabs showed a decrease in the percent fecal dry
matter from 5 mo to 8 mo (P<0.01), the QH did not show a change in percent fecal dry
matter with age (P=0.96). Interestingly, Arabs at 5 mo had a higher fecal matter output
than at 8 mo, but the QH had a higher fecal matter output at 8 mo than at 5 mo (P<0.01).
Although QH urinated more frequently than Arabs, defecation was similar, with the
Arabs at 8 mo defecating less frequently than Arabs at 5 mo, QH at 5 mo, and OH at 8

mo.

Arabs digested more CP than QH when ages were combined (P<0.05), and tended
to digest more energy than QH (P=0.07; Table 9). The digestibility of ADF and NDF did

not differ between breeds at 5 and 8 mo.

Sex effects (treatment, age, and breed combined)

Body weight (P=0.69), feed intake (P=0.23), and water intake (P=0.66) were not
different between fillies and colts (Table 10). Fillies at 8 mo consumed more feed (29:1
g/kg BW/d) than fillies at 5 mo (26:1 g/kg BW/d). Fillies had higher fecal dry matter
than colts, but the fecal output was similar between sexes. QH fillies urinated more often
(15:1 times/d) than QH colts (11:1 times/d), Arab fillies (7:1 times/d), and Arab colts
(8:1 times/d; P<0.05). Quarter Horse colts also urinated more often than Arab colts
(P<0.05). Overall, fillies and colts urinated the same number of times each day, but colts

defecated more often than fillies.

34

CP digestibility tended to be higher in fillies than in colts (P=0.08; Table 10).
There was no difference in digestibility of ADF, NDF, or energy between fillies and

colts.

35

Table 5: Mean : SE body weight, feed intake, water intake, fecal output, frequency of
urination, and frequency of defecation of all weanlings in High Con, Equal, and Low Con
treatments with age, breed, and sex combined.

 

 

Measurement Treatment Mean : SE
High Con 229:7
Body Weight Equal 233:7
(kg) Low Con 228:7
High Con 29:1
Feed Intake Equal 29:1
(g/ kg BW/d) Low Con 28:1
High Con 55:5
Water Intake Equal 63:5
(g/ kg BW/d) Low Con 63:5
High Con 27.6:O.Sa
Fecal DM Equal 25.4:05b
(%) Low Con 24.6:O.5b
High Con 8.0:O.4y
Fecal Output Equal 8.6104xy
(g/ kg BW/d) Low Con 9310.4"
High Con 11:1
Urination Equal 10:1
(times/day) Low Con 10:1
High Con 11:1b
Defecation Equal 12:1b
(times/day) Low Con 16:1a

 

abValues within a measurement lacking common superscripts differ (P<0.05)

xyValues within a measurement lacking common superscripts tend to differ (P<0. 10)

36

Table 6: Mean : SE CP, ADF, NDF, and energy apparent digestibility of all weanlings in.
High Con, Equal, and Low Con treatments with age, breed, and sex combined.

 

 

Measurement Treatment Mean : SE
High Con 73.9:1.6a
CP Digested Equal 68.8:1.6ab
(% ) Low Con 63.9:1.6b
High Con 32.6:2.9
ADF Digested Equal 333:2.9
(%) Low Con 39713.0
High Con 34.8:2.3y
NDF Digested Equal 34.7:22y
(%) Low Con 41.4:23"
High Con 72.1.:14"
Energy Digested Equal 69.7:1.3xy
(%) Low Con 67.0:1.4y

 

abValues within a measurement lacking common superscripts differ (P<0.05)

xyValues within a measurement lacking common superscripts tend to differ (P<0.10)

37

Table 7: Mean 1 SE body weight, feed intake, water intake, fecal dry matter, fecal output,
and frequency of urination and defecation of horses in High Con, Equal, and Low Con
treatments at 5 and 8 mo.

 

 

Measurements Treatments 5 mo 8 mo
High Con 199:7a 25917b
Body Weight* Equal 203:7a 259:7b
(kg) Low Con 199:7a 259:7b
High Con 2811 2911
Feed Intake Equal 28:1 2911
(g/ kg BW/d) Low Con 2811 2911
High Con 61:4 50:4
Water Intake* Equal 69:4 59:4
(g/ kg BW/d) Low Con 64:4 6214
High Con 28.7105 26.9105
Fecal DM* Equal ' 25.5105 25.4105
(%) Low Con 25.0105 24.1105
High Con 79:03 8.1103
Fecal Output Equal 8.5103 8.3103
(g/ kg BW/d) Low Con 9.5103 9.1103
High Con 12:1x 11:1x
Urination* Equal 11:1x 9:1y
(times/day) Low Con 12:1x 9:1y
High Con 1111 10:1
Defecation* Equal 13:1 1 1:1
(times/day) Low Con 1611 1511

 

ab Values within a measurement lacking common superscripts differ (P<0.05)

xyz Values within a measurement lacking common superscripts tend to differ (P<0.10)

* Overall 5 mo different than 8 mo, regardless of treatment: P<0.05

38

Table 8: Mean : SE CP, ADF, NDF, and energy apparent digestibility of horses in High
Con, Equal, and Low Con treatments at 5 and 8 mo.

 

 

 

Measurements Treatments 5 mo 8 mo
High Con 74611.83 73.211.83b
CP digestibility* Equal 68.711.8bc 69.011.8bc
(% ) Low Con 67.711.8C 60.111.9d
High Con 29.4134 36.0133
ADF digestibility Equal 30113.4 35.9133
(%) Low Con 40313.4 40013.6
High Con 32.6:2.9 37012.8
NDF digestibility Equal 33212.9 36312.9
(%) Low Con 41512.8 41313.1
High Con 71511.2 72611.2
Energy Digested Equal 69.2112 71.1112
(%) Low Con 67311.2 66.7113
ab

39

Cd Values within a measurement lacking common superscripts differ (P<0.05)
* Overall 5 mo greater than 8 mo, regardless of treatment: P<0.05

Table 9: Mean : SE body weight, feed intake, water intake, fecal dry matter, fecal

output, frequency of urination and defecation, and CP, ADF, NDF, and energy apparent ‘
digestibility of Arabians and Quarter Horses at 5 and 8 mo.

 

Measurements Arabians Quarter Horses

5 mo 8 mo 5 mo 8 mo
Body Weight (kg)* 19016d 24616b 21117c 27317a
Feed Intake (g/kg BW/d) 3011a 2711b 2611b 31113
Water Intake (g/kg BW/d) 59:4 5414 701-4 5914
Fecal DM (%) 27.8104a 26210.4b 24.7104C 24.7104C
Fecal Output (g/kg BW/d) 9.1103a 8010.3b 8110.4b 9310.4al
Urination (times/day)* 9:1 611 1411 12:1
Defecation (times/day) 1411a 1111b 1311al 1311a
CP digested (%)* 73.0115 69.4115 67.6115 65511.5
ADF digested (%) 36.0129 39.8126 31.0128 34.2129
NDF digested (%) 37912.4 40.4122 33.6124 36012.5
Energy digested (%ff 70611.2 71.7112 67611.2 68411.2

 

abd

C Values within a measurement lacking a common superscript differ (P<0.05)

* Overall differences between breeds when 5 and 8 mo combined, regardless of age: P<0.05

T Overall trend in differences between breeds, regardless of age: P<0.05

40

Table 10: Mean 1 SE body weight, feed intake, water intake, fecal dry matter, fecal
output, frequency of urination and defecation, and CP, ADF, NDF, and energy apparent .
digestibility of fillies and colts (Arabs and QH combined).

 

Measurements Fillies Colts
Body Weight (kg) 22816 23216
Feed Intake (g/kg BW/d) 26:1 3011
Water Intake (g/kg BW/d) 59313.8 61.7137
Fecal DM (%) 26.510.4° 25210.4b
Fecal Output (g/kg BW/d) 8.4103 8.9103
Urination (times/day) 11:1 10:1
Defecation (times/day) 1211a 1411b
CP digested (%) 70611.3 67.1113
ADF digested (%) 36312.4 34.1123
NDF digested (%) 38611.9 35.4119
Energy digested (%) 70611.1 68511.1

 

b . . . . .
a Values W1thln a measurement lacklng a common superscript d1ffer(P<0.05)

41

CHAPTER 4

DISCUSSION

Weight gain of horses did not differ between treatments or between sexes. This
similarity in body weights between colts and fillies is consistent with past research in
which differences are usually not found until the animals are at least 18 mo of age
(Saastamoinen, 1990). OH were heavier than Arabs at 5 and 8 mo; probably because QH
will reach a mature weight of 450 to 600 kg, while Arabs will reach a mature weight of
363 to 450 kg (Evans, 1999). Thoroughbred foals from Canada, Ireland, and Kentucky at
5 and 8 mo are reported to average 234110 and 280110 kg, respectively (Pagan etal.,
1996; Jelan et al., 1996). In the current study the QH and Arabs weighed less than the
Thoroughbreds at 5 mo, although the OH weighed about the same as the Thoroughbreds

at 8 mo, while the Arabs still weighed less.

Treatment diets were formulated with feedstuffs frequently used in the industry,
such as corn, oats, and alfalfa-timothy grass hay. In addition, the ratios of concentrate to
roughage were determined to mimic those recommended by the NRC, commonly fed in
the industry, and representing a high roughage diet. Providing young horses ad libitum
access to feed is commonly used in the industry to encourage consumption and growth.
Furthermore, providing ad libitum access to feed may also decrease the intake of large
glucose-yielding carbohydrates over short time periods and help decrease

hyperinsulinaemia, which is often reported in horses that are meal-fed (Frape, 1989).

42

Decreasing hyperinsulinaemia may aid in preventing developmental orthopedic disorders

in young horses (Murphy et al., 1997).

Cymbaluk (1989) found that the energy density of the diet was an important
determinant of feed intake with horses. Weanlings fed a high fiber diet ate up to 26%
more feed than those fed a high concentrate diet (Cymbaluk, 1989). However, in the
current study, the nutrient composition of the treatment diets did not alter the amount of
feed consumed by the weanlings. Additionally, a preference study done by Hawkes et al.
(1985) found that even though ponies demonstrated preferences, the total intake per meal
was not greatly decreased when the less preferred feed is fed alone. Voluntary dry matter
intake of ingested feeds may be difficult to predict from simple characteristics such as

protein and fiber levels (Dulphy et al., 1997).

The primary difference between the previous study and the present study is the
pelleting of the diets. Cymubaluk and Christensen (1986) found no difference in intake
rates when mature horses were fed unpelleted and pelleted diets of alfalfa. However, rate
of passage is faster with diets higher in fiber (Ellis, 2002), which may also increase the
dry matter intake. Over a 63-d study, Hintz (1966) found that the pelletin g of feed did
not have an effect on the growth of young horses, and the diets were consumed, digested

and utilized similarly to diets that were not pelleted.

43

Intake in horses is generally perceived to be regulated primarily by physical
qualities of the forage such as taste, odor, toughness, and ease of sorting. Mature horses '
will ingest about 20.8 g DM/kg BW/d(Du1phy et al., 1997), while the growing horses in
the current study consumed approximately 29 g/kg BW/d. These weanlings consumed
the same amount of feed when fed different treatment diets, suggesting that they relied
primarily on gut distension to regulate feed intake since the treatment diets had the same
DM and similar weights per volume, but different energy, protein, and fiber
concentrations. Feed intake was not different in horses at 5 and 8 mo, perhaps because

weanlings at 5 and 8 mo are still growing at nearly the same rate (Jelan et al., 1996).

There were some factors in the study that could not be controlled; temperature,
location, and diets fed between digestibility trials. Thus, some of the related data may not
be biologically significant. For instance, weanlings drank more water at 5 mo than 8 mo,
however, the ambient temperature probably had a greater influence than the age of the
horses (Crowell-Davis et al., 1985: Scheibe et al., 1998). Horses were 5 mo of age
during the months of July through October in Michigan with temperatures averaging
22°C, and horses were 8 mo of age during the months of October through January with

temperature often below freezing (www.weatherchannel.com).

In the present study, water intake during the 4-d digestibility studies was not
affected by the treatment diets. This is in contrast to a study by Fonnesbeck (1968) in
which adult horses fed all-roughage diets consumed more water than those fed mixed

concentrate-roughage diets presumably because of the varied fiber content in the diets as

opposed to the percent BM in the diets. In the present study, all treatments contained
varied fiber levels, but there were no differences in the percent DM of the treatments as
there was in the Fonnesbeck (1968) study. In the current study, dietary fiber content did
not affect water intake, but perhaps if the horses on the current study were fed the diets
for a longer time or fed a non-pelleted diet, water intake would correlate with previous

research.

Water excretion in feces has been associated with protein, mineral, and fiber
content of the diet (Fonnesbeck, 1968). The current study found percent fecal DM was
greatest in horses fed High Con which had the highest amount of protein digested and the

least amount of fiber in the diet. .

The quantity of feces is the main factor contributing to fecal water excretion;
furthermore the quantity of feces depends on DM intake, DM digestibility, and DM of
feces (Fonnesbeck, 1968). In the present study, weanlings consuming Low Con tended to
have a greater fecal output than High Con due to the increased metabolic components
(endogenous excretions) and residual (undigested) feed components (Maynard et al.,

1979). This agrees with Fonnesbeck (1968) and more recently Gunter (1993).

Diets higher in fiber generally produce greater amounts of feed residue which

require an increased amount of water for excretion and cause retention of more water as

the bulky matter passes through the digestive system (Frape, 1998). Horses fed the Low

45

Con may have defecated more often simply to allow for the passage of the increased fecal

matter as compared to those horses fed Equal and High Con.

Similar to Gibbs and Potter (2002), the High Con had higher apparent crude
protein digestibility than Low Con at both 5 and 8 mo. This could be due to the increased
availability of the protein in the high concentrate diet as opposed to the low concentrate
diet, which was formulated to derive a higher percentage of its protein from the hay
(roughage) portion of the complete feed. Interestingly, Slade (1970) reported that while
apparent digestibility studies reported an increase in apparent nitrogen digestibility when
nitrogen in the diet is increased, true digestibility studies (endogenous N is subtracted
from the fecal N) report similar digestibility values for a range of dietary nitrogen
concentrations. A correlation may exist between fecal DM and crude protein
digestibility. In the present study, there was an increase in DM of the feces as crude

protein digestibility increased. This trend has also been reported by Grenet et al. (1984).

Digestibility of ADF did not differ between treatments; however, horses fed the
Low Con tended to digest a higher percentage of NDF than both the Equal and High Con
treatments. This is in agreement with past research that indicates when grain proportions
were increased in the total diet, the efficiency of fiber utilization decreased in adult
horses (Martin-Rosset and Dulphy, 1987). Similarly, Drogoul et al. (2001) found that
although the mean retention time of the ingesta in the gastrointestinal tract was higher in
horses fed grain (concentrates) in addition to hay (roughages), the efficiency of fiber

utilization was decreased in those horses fed a diet of both hay and grain. This most

46

likely is partly due to the faster the passage of ingesta through the entire gastrointestinal
tract as the hay to grain ratio consumed is increased (Drogoul et al., 2001). The extent of.
fiber digestion is determined by the time the fiber stays in the hindgut region, the rate and
amount of microbial fermentation activity in the hindgut, the ratio of roughage to

concentrate consumed, and the type and quality of forage fed.

Potentially the 10-d diet adaptation period was sufficient to encourage microbial
growth and allow greater ADF digestion in horses fed the Low Con. Furthermore, Grenet
et a1. (1984) reported that the percentage of fecal DM may increase when forage fiber
digestibility decreases. This relationship occurred; a trend to increase NDF digestibility
in the Low Con resulted in a decrease in fecal DM from the horses fed the Low Con diet.
Horses in the High Con treatment tended to digest a higher percentage of energy than
those in the Low Con treatment. This has been found by many researchers, including

more recently Drogoul et al. (2001).

The research protocol could be improved by eliminating the effects of location,
temperature, and diets fed between digestibility studies. The number of horses was
adequate especially if they could all be housed at the same facility to enable the
comparison of breed without confounding effects. Since the 4-d digestibility study was
done with horses in stalls, it may have been beneficial if the horses were individually
stalled during the 10-d adjustment period. Pellets were excellent to assure consumption
of exact ratios of concentrate to roughage while feeding ad libitum, but the pellets may

have had an effect on digestion.

47

In conclusion, horses fed any of the three treatment diets consumed enough
nutrients to meet the current nutritional standards for weanlings based on the amount
consumed and the digestibility of nutrients in the treatments (Table 11; NRC, 1989).
Cymbaluk (1989) found that horses fed free choice will consume 20 to 50% more energy
than suggested by the NRC for moderate growth. In the current study, all three
treatments consumed energy values suggested by the NRC (1989) but a long-term study
with the diets may find different results. Ott et al. (2002) suggests feeding weanlings
1.54 to 1.70 kg of 90% DM concentrate for each 100 kg BW daily and providing ad
libitum access to forage to consume adequate energy for maximum growth. The
weanlings in the present study, in all three treatment groups, consumed about 2.9% of
their BW daily which is equivalent to consuming 2.7 kg feed / 100 kg BW/ d total feed for
a 230 kg horse (average size of all weanlings) during the digestibility studies. Thus, only
the High Con group consumed greater than 1.54 kg/100 kg BW/d of concentrate as

suggested by Ott et al. (2002).

All weanlings consumed the NRC recommended amount per day of protein.
Amino acid profiles were not explored beyond lysine and the amount of digested protein
needed by weanlings is still unknown. Under usual feeding conditions with conventional
feeds, if the lysine is adequate, then the other amino acids are usually considered
adequate (Hintz, 1986). It has been suggested that the NRC (1989) requirements for dry
matter intake, digestible energy, and protein are excessive for weanling horses (Ott et al.,

2002). Furthermore, there are currently no recommendations for fiber. Although fiber

48

should be fed to maintain health and welfare of the horse, too much fiber could dilute the
energy and nutrients of the total diet. Thus, the complete diet for weanlings should be
formulated to contain balanced nutrients for feeding ad libitum, but more importantly,

must contain the digestible nutrients needed for maintenance and growth.

49

Table 11: Requirements for weanlings at 6 mo expected to reach 500 kg mature BW, but
currently weighing 215 kg and consuming 2.9 % BW/d; NRC recommended diets
compared to High Con, Equal, and Low Con treatment diets.

 

 

NRC High Con Equal Low Con
Concentrate: 70:30 70:30 50:50 30:70
Roughage

Adjusted BW 215 215 215 215
% BW consumed 2 - 3.5 2.9 2.9 2.9
Kg/d consumed 4.3 - 7.5 6.2 6.2 6.2
GB Mcal energy - 24.7 24.3 24.4
DE digested (Meal) 15.0 - 17.2 17.8 17.1 16.3
CP consumed(g) 750 - 860 870 936 796
CP digested (g) - 643 644 509
ADF consumed (g) - 1023 1091 1428
ADF digested (g) - 333 363 567
NDF consumed (g) - 1858 1821 2207
NDF digested(g) - 647 632 914

 

CHAPTER 5

IMPLICATIONS

Results of this study showed a difference in the ability of weanlings to digest
protein and fiber in diets with varying concentrate to roughage ratios. Future research is
needed to determine the amount of nutrients absorbed and utilized from the diets, not just

the amount consumed and digested of the treatment diets.

The current requirements for equine diets are guided by feed values, not
digestibility of the feeds in each class of horse. Given that the current study only
documented differences during two short-term periods, a long-term feeding trial with the
diets would be instrumental in determining how the diets would be absorbed and utilized,
and if any of the diets would result in negative outcomes such as increased cost, behavior
problems, decreased growth, increase incidence of developmental orthopedic disorders,

or gastro—intestinal problems.

The current study indicates that any of the three diets would provide the
weanlings with the nutrients at the levels currently recommended by the NRC (1989).
Currently in the industry, many managers feed weanlings less than the NRC
recommended 70% concentrate presumably to avoid possible problems associated with
feeding high concentrate — low fiber diets (Gibbs and Cohen, 2001; Jelan et al., 1996).
Furthermore, feeding diets high in fiber to weanlings prone to developmental orthopedic

disorders may be beneficial. Feeding a hi gh-fiber diet dilutes dietary energy

51

concentrations and enables the diets to be fed free-choice which may reduce future
behavioral problems and promote equine welfare. There is limited available research

conclusively supporting either feeding high concentrate or high fiber diets to weanlings.

Horse managers can formulate feed to provide weanlings nutrition to suit
immediate goals and future expectations of soundness and digestive health. Although the
current study shows that the weanlings digested the needed nutrients, feeding high fiber
diets to young horses should be done with caution. Long-term studies of the diets used in
the study are not available, and such diets may not be beneficial to the weanling as it
matures. A future multiple-year study to explore the cumulative effects of high
concentrate or high fiber diets on growth, development, and performance would be
extremely useful to horse managers. The optimum growth rate and nutrient intake for
productivity and longevity has not been determined; however an optimal nutrient to

energy ratio in the diet is most important (NRC, 1989).

52

CHAPTER 6

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58

APPENDIX

Table 1A: Mean 1 SE wither height, hip height, and cannon bone circumference
(Cannon C) of Quarter Horses and Arabians at 5 and 8 mo.

 

 

0H Arab
5 mo 8 mo 5 mo 8 mo
Wither Height (cm)* 125.0113 132.4113 125.4113 134.4113
Hip Height (cm) 132.0114b 139.3114a 128.5114b 138811.43
Cannon C (cm)* 24511.2 31911.2 28511.2 38811.6

 

ab Values within a measurement lacking common superscripts differ (P<0.05)
* Overall 5 mo less than 8 mo, regardless of breed: P<0.05

Table 2A: Average individual feed consumption (g/kg BW/d) of High Con, Equal, and
Low Con by weanlings at 5 and 8 mo during the 10-d adjustment period.

 

 

Treatment 5 mo 8 1110*
High Con 27211.4 35.0120
Equal 27.1115 38.4122
Low Con 25311.4 36.7125

 

I 8 mo greater than 5 mo, regardless of treatment (P<0.05)
*Overall QH consumed less than Arabs, regardless of age or treatment: P<0.05

59

Table 3A: Average as-fed calculated values for energy, CP, Ca, and P for whole oats,
protein pellets, Purina Strategy feed, grass pasture, grass hay, and mixed hay.

 

 

DM Energy CP Fiber Ca P

4%) (Meal/kg) 1%) (%) (%) 4%)
Whole oats 89 2.85 11.8 10.7 0.08 0.34
Protein pellets* 90 - 32.0 8.0 1.3 0.8
Purina Strategy 90 - 14.0 8.0 0.80 0.60
Grass pasture 29 0.58 2.7 9.8 0.11 0.09
Grass hay 90 1.74 8.5 30.0 0.38 0.18
Alfalfa/grass hay 90 1.90 12.8 27.8 0.81 0.20

 

* Calf protein pellets (company name)

60

APPENDIX:
EQUINE CAECAL CONTENTS, EXTIMATION OF TOTAL CELLULOLYTIC
NUNIBERS IN ADULT HORSES

INT RODUCTION/ LITERATURE REVIEW

There is sizeable variation in management and feeding practices of domestic
horses across the world and throughout history. This is reflective of the many uses for
horses and the availability and costs of suitable environments and feedstuffs. The horse
has developed specific digestive physiology, anatomy, and feeding behaviors associated
with a high fiber diet consumed through grazing and browsing. Prior to domestication,
horses survived on a diet consisting solely of available forages containing relatively large
amounts of water, soluble proteins, lipids, sugars, and structural carbohydrates, but very
little starch (Frape, 1998). Additionally, wild horses consume multiple meals throughout
the day and night during short, frequent feedings. The art of feeding domestic horses of
all classes is to provide the needed nutrients for service and performance while avoiding

digestive and metabolic upsets resulting from feeding methods and ingredients.

The gastrointestinal tract of the horse is comprised of a small, simple stomach, a
long small intestine containing relatively little volume, a large caecum, and a sacculated
hind gut. This anatomy allows the horse, a nonruminant herbivore, to digest fibrous

diets.

61

At birth the foal is completely dependent on milk and the digestive system grows,
develops, and becomes inoculated with microbes in the first year to enable the horse to
digest starches and eventually fibers. The ability to digest fiber is important to both
domestic and wild horses. In the wild, once the horse is weaned from its dam, high fiber
diets will be the basis of its diet. Although in domestic horses the amount of fiber in the
horse’s diet varies considerably with its intended use, adult horses are typically fed
significantly more fiber than young horses; often receiving diets of 100% hay or grass.
The age when the digestive system is fully developed and able to utilize the nutrients
available in high fiber diets and the factors that initiate these changes have not been

definitively determined.

The equine digestive tract continues to develop from birth through maturity.
During the time after weaning, the large intestine grows faster than the remainder of the
gastro-intestinal tract to accommodate the increased consumption of fiber in the diet
(Frape, 1998). Although the proximal regions (stomach and small intestine) grow very
little after birth, the distal regions (caecum and large intestine) continue to grow and
develop until the horse is nearly 20 years old (Frape, 1998). However, digestion in the
caecum and ventral colon depends almost entirely on the activity and vitality of the
microflora of this region (Fonnesbeck, 1968; Vander Noot and Gilbreath, 1970).
Inoculation of the hindgut is primarily done through coprophagy and ingestion of
microbes during play, social, and exploratory behaviors (Fransis-Smith and Wood-Gush,

1977; Crowell-Davis and Houpt, 1985; Galef, 1979)

62

Horse feeds can generally be divided into two primary classes of feeds: roughages
and concentrates. Roughages generally contain at least 20 % crude fiber (air-dry basis). 1
Typically, roughages are fed to provide nutrients, reduce dry matter intake when mixed
with other feeds, decrease the net energy intake of the total diet, maintain an active
microbial population in the large intestine and caecum, and promote equine welfare
through decreasing possible diet-associated behavior problems. Nutrient quality of
roughages can vary and depends on type of roughage, climate effects, soil fertility, and

stage of maturity when harvested (Hintz, 1983).

Concentrates are the portion of the horse’s diet comprised of feeds rich in starch,
protein, or both, and typically contain less than 15 to 17 % crude fiber (Frape, 1998).
They are most often fed to increase the energy and nutrient concentration of the total diet
in growing. breeding, or working horses. Nutrient content and formulation must be
thoroughly investr gated when feeding mixed concentrate diets because the concentrate
ingredients in the concentrate can drastically vary in nutrient concentrations (Pond,
1995). Furthermore, high concentrate diets have been associated with colic, founder, and
other physiological and digestive upsets in horses (Garner et al., 1978; Goodson et al.,
1988). Therefore, there is increasing interest in determining which roughages are
digested best to enable feeding higher levels of roughage while still maximizing growth,

reproductive, and athletic performance.

Crude fiber describes the fiber portion of feed, but does not separate the

carbohydrates into highly digestible and less digestible portions. Fiber is often described

as acid detergent fiber (ADF) and neutral detergent fiber (NDF) to describe components
that are mostly available, incompletely available, and mostly unavailable (Van Soest,
1987). The NDF portion contains the plant cell wall: hemicellulose, cellulose, and lignin,
while ADF is representative of only cellulose and lignin. The soluble portion of a fiber
sample is composed of cell contents and is made up of soluble carbohydrates, such as
starch, organic acids, protein, and pectin (Maynard et al., 1979). Thus, the soluble

portions are the most available, while the insoluble portions are partially available.

Horses digest relatively the same amount of fiber as mules, donkeys, zebras, and
elephants (monogastrics); yet they digest less fiber than kangaroo (monogastric
herbivore), chinchillas (monogastric herbivore), and ruminants (Evans, 1999). Koller et
al. (1978) reported that ruminal microbes in cows fermented all timothy, orchard grass,
and wheat straw at a faster rate than horses accustomed to an all hay diet. However,
alfalfa was fermented at the same rate, presumably because the alfalfa used was of high
quality and contained minimal indigestible fibers such as the cell wall and lignin. The
ferrnentability of fibrous feedstuffs is dependent on the animal species, microflora
present, microflora activity, and time ingesta is exposed to microbes (Sunvold et al.,
1995). Fiber digestion in the horse is correlated to three main factors: the composition of
the diet, especially the carbohydrate portion, the fibrolytic activity of the microbial
ecosystem, and the rate of passage of the digesta through the digestive tract, especially in

the hindgut (Drogoul et al., 2001).

64

Although, bacteria, protozoa, and fungi are all active in the hindgut of the rumen,
bacteria have been the most studied symbiotic organisms present in the hindgut of the
horse (Lee et al., 2000; Roderick and Wilkins, 1988). Different types of bacteria are
present throughout the digestive tract of the horse. Equid require a nitrogen sources other
than ammonia or urea, however energy derived from microbial activity is a vital part
source of energy for the horse (Maczulak et al., 1985). Microbial action in the hindgut
forms primarily acetate, propionate, butyrate, and small amounts of other acids. The
amount of acids produced per unit dry-matter intake, and their relative proportions,

depends directly on the nature of the feed fed to the horses (Fombelle et al., 2001).

An abrupt dietary change may be especially harmful to the hindgut microflora. A
sudden change from a high roughage diet to a high concentrate diet increases the numbers
of total viable anaerobic bacteria and lactobacilli in the caecum, while bacilli,
xylanolytic, and pectinolytic bacteria decrease (Garner et al., 1978; Goodson et al., 1988).
These changes have been associated with a decrease in pH and an increase in lactate
(Garner et al., 1978; Goodson et al., 1988). More recently, Fomelle et al. (2001) reported
changes in numbers and activities of microbial communities in the hindgut of horses in
only 5 h after an abrupt incorporation of barley into a diet that was previously comprised

of 100% meadow hay.

The microbial profile and the biochemical composition of the hindgut are

correlated to the roughage to concentrate ratio fed (Moore et al., 1993). Drogoul et al.

(2001) report that fiber digestibility is reduced as the amount of grain in the diet is

65

increased. They explained this by the premise that the bacteria attack the simpler
carbohydrates by preference, and the rate of passage is increased which decreases the
available time for digestion to occur in the hindgut. In sheep, those fed a 60%
concentrate diet had higher percentages of starch digesters and lower percentages of
cellobiose-fermenting bacteria in the rumen as compared to sheep consuming a 100% hay
diet (Dehority and Grubb, 1976). High concentrate diets increase the total bacteria,
mostly due to the increase in amylolytic bacteria concentrations (Moore, 1993). Julliand
et al. (2001) reported a ten-fold increase in lactate, the main end product of amylolytic
population’s fermentation, in the caecum and colon of horses fed 50:50 diet as compared
to those fed a 100:0 (all hay) diet. Furthermore, when high starch diets decrease the pH
in the hindgut, there is an increase in population and activity of lactobacilli and
streptococci, normal inhabitants and major starch utilizers (Hungate, 1966; Garner et al.,

1978).

Interestingly, the equine hindgut ecosystem responds similarly to ruminants when
concentrates are introduced to 100% roughage diets (Fomelle et al., 2001). When starch
is included in the diet, it increases the soluble carbohydrates in the diet which causes an
increase in the rate of micro-organism multiplication followed by a chain of reactions
(Dawson et al., 1997). Most importantly, a saturation of the digestive ecosystem’s
buffering system occurs which decreases the pH and thus, decreases cellulolytic bacteria
and increases acidophilic flora such as lactobacilli and streptococci (Dawson et al., 1997;

Goodson et al., 1988). This in turn causes a decrease in acetate, and an increase in lactate

66

and propionate (Hintz et al., 1971; Willard et al., 1977). If these changes are drastic, they

can result in laminitis, colic, and even death (Garner et al., 1978).

Changes in the gut mircoflora can be devastating in horses that over-eat
concentrates and suffer from colic or acute equine laminitis, which is often deadly or
severely handicapping. Garner et al. (1978) quantified caecal bacteria flora before and
after horses overate concentrates. The onset of laminitis is characterized by intracaecal
proliferation of lactobacilli and thus increased lactic acid production and increased amine
production (Garner et al., 1978; Bailey et al., 2002). An increased intracaecal acidity
reduced caecal Enterobacteriaceae and anaerobic Streptococci numbers 8 h after
carbohydrate overload. While Streptococci tended to re-establish its population after 24

h, the Enterobacteriaceae continued to decrease.

Fiber utilization is extremely important to the health and survival of the horse.
However, specific information regarding the enumeration and characterization of the
microbes in the equine caecum is still limited. Three main ruminal cellulolytic bacterial
species have been identified in the adult horse: F ibrobacter succinogenes, Ruminococcus
flavefaciens, and Ruminococcus albus (Bonhomme, 1986; de Vaux, 1998). Furthermore,
Bacteroides sp., Bacillus cellulosae dissolvens, Clostridium sp., Eubacterium sp., and
Butyrivibriofibrisolvens have also been observed (J ulliand et al., 1999). However, the
entire diversity of the hindgut microbes and whether their structures depend primarily on

the diet or individual animal remain unclear (Julliand et al., 1999).

67

Determination of the number of total anaerobes and cellulolytic bacteria is
important to enable the study of normal and diseased states in horses at different ages fed '
different diets. Although it is know that the plant cell wall is digested by bacteria,
protozoa, and fungi in the cow rumen, the degree to which each microorganism
participates is still not clearly defined (Lee et al., 2000). Although there are many
similarities in the microbial populations of the horse and ruminants, the microbes of the
equine caecum have been investigated much less than the rumen. The amount of total
anaerobic microbes and cellulolytic degrading microbes is important to determine for
every class and type of horse to enable future characterization of the microbes and a

clearer understanding of fiber digestion.

The objective of this study was to determine the total anaerobic and cellulose

degrading bacteria numbers in the caecal contents of adult horses.

MATERIALS AND METHODS

Caecal contents were obtained within an hour of death from euthanized horses
(n=6) via a midline abdominal incision to exteriorize the caecum; an enterotomy incision
of the the apex of the caecum allowed for collection of ingesta. Horses were euthanized
at the Michigan State University Veterinary Diagnostic Laboratory and were either

Michigan State University owned research horses or donated by their owners for research

68

(approved by R. Fulton, DVM). Horses had clinically normal gastrointestinal systems

and were euthanized for reasons not related to the gastrointestinal tract (Table 1).

Samples were collected into sterile 120 cc specimen containers with minimal head
space air (to minimize oxygen exposure) and transported to the laboratory on ice. In the
laboratory, contents were shaken to dislodge cellulolytic bacteria from particulate matter,
and 60 cc of the fluid phase of the ingesta was centrifuged at 1000 rpm for 10 min to

separate fluid from particulate matter.

Serial dilutions were used to estimate total and cellulolytic anaerobic bacteria
numbers. Traditional serial dilutions were performed by adding 1 ml of the centrifuged
ingesta to 9 ml of anaerobic cellulose degrading media (Table 2) and general anaerobic
media (Table 3). One ml of each new solution was drawn out of each Hungue tube or
Wheaton jar and added to another 9 ml of either the cellulose selective media or standard
anaerobic media. This process was continued to make dilutions of 1:10, 1:100, 1:1000,
1:10000, 1:100,000, and through to a dilution of 1:10”. Serial dilutions were replicated
three to five times and preformed for cellulolytic and general anaerobe enumeration.
Anaerobic and cellulolytic media was prepared and stored at room temperature until used

in the laboratory (Dehority et al., 1989).
After the inoculated cultures were serially diluted into the anaerobic medium and

incubated at 37°C for 2 weeks, the numbers of cellulose degrading bacteria and total

anaerobes were estimated by observing the vials for the degradation of cellulose disks in

69

the cellulolytic medium and the cloudy appearance in the anaerobic media (Cochran,
1950; Dehority etal., 1989). Total anaerobic numbers and cellulolytic bacteria

degradation was checked every 24 h and monitored for 14 (1.

RESULTS

The concentrations of total viable bacteria in the caecal fluid from the caecal
contents of the adult horses ranged from 103 — 107 microbes/ ml caecal fluid (Table 4).
Thus, there was an average of 108 anaerobic microbes/ ml caecal fluid. The
concentration of cellulolytics within the samples resulted in a range of 106 - 109 microbes/

ml with an average concentration of 105 microbes/ ml (Table 5).

Because of the limited number of horses and unknown nutritional background of
some of the horses (Table 1), we were unable to compare the effects of age, diet, and
gender on the anaerobic microbes in the caecum at this time. However, during the
degradation of the cellulolytic disks in the cellulolytic media, the disks turned from white

to yellow. Cellulolytic bacteria comprised about 64% of the total anaerobes (Table 6).

70

DISCUSSION

When the population of bacteria from the caecum samples were introduced to the
nutrient rich medium, the organisms showed four major growth phases: the lag phase
(metabolically active, adjusting to new media), the logarithmic phase (population
growth), the stationary phase (number of live cells stays constant), and the decline phase
(decrease in cell number at a logarithmic rate) to form the standard bacterial growth curve
(Black, 1999). All caecal samples resulted in some growth of both anaerobic and
cellulolytic bacteria. Mackie and Wilkins (1988) examined the duodenum, jejunum,
ileum, caecum, and colon for total culturable and proteolytic bacteria in mature (3 to 5 yr)
horses. As would be expected, they found a 100 fold increase in the number of both
groups of bacteria in the caecum and colon as compared to the samples retrieved from the
forgut of horses. Kern et al. (1974) reported that cellulolytic bacteria numbers were

greater in the caecum than the terminal colon and stomach.

In the current study, the approximate number of cellulolytic bacteria, total
anaerobes, and the resulting ratio was higher than has previously been reported in the
literature. Interestingly, the horses used in the current study were all older than the
mature horses usually used which are 3 to 10 years of age when age is reported.

The cellulolytic bacteria counts in the current study (average 105) were higher than those
reported by Jullian et al. (1999), Goodson et al. (1988), and Kern et al. (1974).
Additionally, the percentage of cellulolytic bacteria of the total anaerobes was much

higher than 3.8% and 9% previously reported (Julliand et al., 1999; Kern et al., 1974).

71

Their counts were estimated with probes. In the current study, the lowest value possible
to obtain was 10% (101 divided by 1010); however, the lowest count actually found was

43%.

Interestingly, as the cellulolytic discs dissolved, they turned from white to yellow
in color. This yellow color is a unique and well known trait of Ruminococcus
F lavefaciens, one of the three main rurrrinal cellulolytic bacterial species that has been
identified in ruminants, horses, and rats (J ulliand et al., 1999; Macy et al., 1982). Further
investigation under a microscope and DNA probe will be useful in positive identification

of all the cellulolytic and total anaerobic bacteria present in the collected caecal contents.

The most probabley numbers, MPN, method will be helpful in future studies used
simultaneously with the serial dilutions (Dehority et al., 1989; Cochran, 1950). Dilutions
were made based on the estimated bacterial numbers within the sample. Over time, as
the dilutions increased, a point was reached when some tubes contained organisms, while

others did not show any growth.

Continued enumeration and classification of equine hindgut microbes will aid in
the understanding of the microbe’s structures and whether these structures depend on the
diet or on other factors linked to the animal’s unique characteristics. Further
understanding of both the normal and diseased hindgut activity could lead to a decrease
in deaths and disease related to gastrointestinal disorders and an economic gain to the

horse industry. Nonbacterial direct-fed microbials are commonly used in the livestock

72

industry, but their use in horses is only beginning to be explored (McDaniel et al., 1993;
Weese, 2002). In the future, inoculation of horses with poor fiber digestion and young
equines may increase animal welfare by allowing incorporation of a high fiber diet as
well as promote health and longevity of the equine through increased feed and nutrient

utilization.

ACKNOWLEDGMENTS
Thank you Dr. Nielsen and Dr. Yokoyama for facilitating this independent study project

as part of my master’s degree program. Thank you to the microbiology lab in Animal
Science for the use of their equipment and materials.

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Dehority, B. A., P. A. Tirabasso, and A. P. Grifo, Jr. 1989. Most-probable-number
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Galef, B.G. 1979. Investigation of the functions of coprophagy in juvenile rats. J. Comp.
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Garner, H..,E J .N. Moore, J .H. Johnson, L. Clark, J .F. Amend, L.G. Tritschler and JR.
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Goodson, J ., W.J. Tyznik, J.H. Cline, and BA. Dehority. 1988. Effects of an abrupt diet
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Hintz, H.F., R.A. Argenzio, and HF. Schryver. 1971. Digestion coefficients, blood
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Kern, D.L., L.L. Slyter, E.C. Leffel, J.M. Weaver and RR. Oltjen. 1974. Ponies vs.
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Sunvold, G. D., H. S. Hussein, G. C. Fahey, Jr., N. R. Merchen, and G. A. Reinhart.
1995. In vitro fermentation of cellulose, beet pulp, citrus pulp, and citrus pectin

using fecal inoculum from cats, dogs, horses, humans, and pigs and ruminal fluid
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76

Table l: Horse’s used in random collection: Sex, age, breed, and nutritional history

 

 

Horse Number Sex Age Iyr) Horse history

1 Gelding 15 Standardbred. Pasture supplemented
with mixed hay diet, chronic
obstructive pulmonary disorder,
COPD.

2 Mare 20 Grade horse. Mixed grass hay and
pasture diet. Chronic COPD

3 Mare 20 Grade horse. Diet unknown.

4 Gelding 20 Grade horse. Diet unknown,
presumed to be hay and grass.

5 Mare 11 Grade/Appaloosa. Blind in both
eyes. Presumed to be hay and grass.

6 Gelding l4 Standardbred. Mixed grass and hay

diet. Last 10 d: 5 d moldy hay
followed by 5 d Purina Equine
Senior complete diet

 

77

Table 2: Procedures and recipe for equine caecal cellulose anaerobic media

 

1. Prepared 40 Hungute tubes by cleaning and placing four Whatman No. 1 flilter paper
discs into each tube. Discs were formed with a standard hole punch.

2. Prepare media. Mix ingredients in the order listed, while stirring with a mechanical
stirrer.
To make 600 m] mix:
1200 mg Trypticase peptone
300 mg Yeast extract
45 ml Mineral l: 0.6% K2HPOa
45 ml Mineral 2:
0.6 g KH2P04
0-6 g (NH4)2304
1.2 g NaCl
0.25 g MgSOa - 7H2O
0.16 g CaCl2 - 2H20
0.6 ml Resazurin solution:
25 mg resazurin dissolved in 100 ml distilled water
6 ml Hemin solution:
50 mg hemin dissolved in 1 ml 1N NaOH. Make to 100 ml with distilled
water.
Autoclave at 121 C for 15 min.
120 ml Rumen fluid:
Spin stored rumen fluid at 10,000 RPM for 10 min.
300 mg Cysteine HCl
30 ml 8% Na2C03 solution
353.4 ml distilled water

3. pH solution to 6.8

4. Bring to a full boil over Bunsen burner with CO2 blowing into flask
Let cool, assure CO2 continuing to blow over solution

5. Add 9 ml media to each Hengue tube and seal tightly assuring anaerobic conditions

6. Autoclave
20 minutes at 120°C

 

78

Table 3: Procedures and recipe for equine caecal general anaerobic media

 

1. Prepared 40 Wheaton bottles by cleaning.

2. Prepare media.
Mix ingredients in the order listed, while stirring with a mechanical stirrer.
To make 500 ml mix:
250 mg Celulose: Dextrose Anhydrous Powder
250 mg Cellobiose
250 mg Soluble starch
250 mg Xylose
1.0 g Trypticase peptone
250 mg Yeast extract
37.5 ml Mineral l: 0.6% K2HPOa
37.5 ml Mineral 2:
0.6 g KH2P04
0.6 g (NHa)2804
1.2 g NaCl
0.25 g MgSOa ' 7H2()
0.16 g CaCl2 - 2H20
0.5 ml Resazan solution:
25 mg resazan dissolved in 100 ml distilled water
5 ml Hemin solution:
50 mg hemin dissolved in 1 ml 1N NaOH. Make to 100 ml with distilled
water.
Autoclave at 121 C for 15 min.
100 ml Rumen fluid:
Spin stored rumen fluid at 10,000 RPM for 10 min.
250 mg Cysteine HC]
25 ml 8% Na2CO3 solution
294.5 ml distilled water

3. pH solution to 6.8

4. Bring to a full boil over Bunsen burner with CO2 blowing into flask
Let cool, assure CO2 continuing to blow over solution

5. Add 9 ml media to each Wheaton bottle and seal tightly assuring anaerobic conditions

6. Autoclave
20 minutes at 120°C

 

79

Table 4: Cellulolytic bacteria activity

 

 

Horse 10'1 10'2 10'3 10“ 10‘5 10'6 10‘7 10'8 10° 10'10
l + + + + + + + + a - -
2 + + +b +al - - - - - -
3 + + + + + +a 4» a - - -
4 + + + + +b + a - - - -
5 + + + +C +d - - - - -
6 + +C +Cl +6 +6 - - - - -

 

+ Degradation of cellulose discs
- No cellulose degradation visible

a . . . . . .
Degradation vrsrble in one out of three repllcatrons

Degradation visible in two out of three replications

C . . . . . .
Degradation Visible in two out of four replications

d . . . . . .
Degradation v1srble in one out of four repllcatrons

80

Table 5: Total anaerobe activity

 

 

Horse 10‘1 10'2 10'3 10“ 10'5 10'6 10'7 10‘8 10'9 10'10

a C

1 + + + + + + + + + -
b

2 + + + + + + + + - -
C

3 + + + + + + + + - -

C

4 + + + + + + + - - -

5 + + + + + + + + + -
d e

6 + + + + + + + + + -

 

+ Cloudy media, visible anaerobe activity
- Clear media, no anaerobe activity

a Degradation visible in four out of five replications

b Degradation visible in two out of five replications

c Degradation visible in one out of five replications
Degradation visible in three out of four replications

C . . . . . .
Degradation vrsrble in two out of four replications

81

Table 6: Estimation of individual, average, and range of cellulolytic bacteria, total
anaerobes, and percent cellulolytic bacteria of the total anaerobes

 

 

Horse number Cellulolytic bacteria Total anaerobes Cellulolytic bacteria
(number/ 1 ml) (number/ 1 ml) (% of total anaerobes)

1 107 108 88%
2 103 107 43%
3 105 107 71%
4 105 106 83%
5 104 109 44%
6 105 10° 56%

Average 105 108 64%

Range 103— 107 106- 109

 

82

VITA

Susan Kathleen Turcott is the daughter of Riley and Mary Lou Turcott and was
born on February 19, 1978 in Petoskey, Michigan.

Following graduation from Petoskey High School, Susan attended Michigan State
University. She received her bachelor of science in Animal Science in May, 2001. She
began graduate school in August 2001 at Michigan State University were she continued
to foster her interest in animal science with research in equine nutrition. In addition to
her course work, Susan continued to be an active participant in the equine industry
through riding and showing. While in graduate school, Susan coached two successful
years of hunt seat and stock seat intercollegiate horse show association riding teams,
taught horsemanship at Michigan State University, and volunteered to help with many
youth, adult, and community extension programs. She enjoys community service,
outdoor activities, and spending time with her friends and family (dogs included).

Susan hopes to continue her active involvement in the equine industry through
helping others to flourish through learning to appreciate and understand the horse.

83

 

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