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thesis entitled

THE EFFECT OF DIETARY ENERGY LEVEL ON FEEDLOT PERFORMANCE.
VISCERAL ORGAN MASS. CARCASS COMPOSITION. AND ACCRETION
RATES OF GROWING LAMBS

presented by

KELLY WAYNE BRUNS

has been accepted towards fulfillment
of the requirements for

MASTER'S degreein ANIMAL SCIENCE

 

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THE EFFECT OF DIETARY ENERGY LEVEL ON FEEDLOT PERFORMANCE,
VISCERAL ORGAN MASS, CARCASS COMPOSITION, AND ACCRETION
RATES OF GROWING LAMBS

By

Kelly Wayne Bruns

A THESIS

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

MASTER OF SCIENCE

Department of Animal Science

1 995

ABSTRACT
THE EFFECT OF DIETARY ENERGY LEVEL ON FEEDLOT PERFORMANCE,
VISCERAL ORGAN MASS, CARCASS COMPOSITION, AND ACCRETION
RATES OF GROWING LAMBS
By

Kelly W. Bruns

Thirty crossbred (Suffolk X Dorset X Rambouillet) wethers were used to
compare performance, visceral organ mass, carcass composition and accretion
rates while consuming either a high concentrate (CONC) or a 100% alfalfa
(ALFA) diet. Diets were fed to appetite with daily feed (Fl) intake measured.
Metabolizable energy values were 2.79 and 2.17 Mcallkg for CONC and ALFA,
respectively. Lambs were started at 30 kg and slaughtered at 52 kg. Internal
organs and fat associated with each organ were weighed. Carcasses were
separated into cuts, and boneless tissue analyzed for dry matter, fat and crude
protein content. Total F I and days on feed were lower (P<.05) and average daily
gain higher (P<.05) for CONC—fed lambs. NO differences were found for
carcass characteristics. Alfalfa-fed lambs had heavier (P<.05) weights than
CONC-fed lambs for: liver, empty gastrointestinal tract, empty small and large
intestine. Protein and fat concentrations in the carcass were unaffected.

Accretion rates of tissue were greater for CONC- than ALFA-fed lambs.

ACKNOWLEDGEMENTS

The completion of this thesis would not have been possible with out the help of
many individuals. For those who have helped to design or conduct the research or
who were instrumental in my education, I am very grateful.

My deepest gratitude is expressed to Dr. Harlan Ritchie for his guidance and insight
throughout my degree program. The knowledge that he has given me concerning
the history and future of the livestock industry is invaluable. His willingness to
provide a detailed answer for the many questions that I ask can never be paid back.
His mannerism and work ethic is one that I hope I can exhibit throughout my career.
It is a privilege to work for such a distinguished and respected individual.

Dr. Werner Bergen deserves much credit for interpreting these research results
and for his valuable counsel in the preparation Of this thesis. The magnitude of
time that he has tirelessly spent molding this neophyte researcher can not be
measured and is greatly appreciated. I am ever indebted to Dr. Bergen for his
unique way Of developing the desire in myself to understand science; truly a
significant accomplishment.

Dr. David Hawkins deserves my most sincere thanks for recruiting me to Michigan
State University and giving this rookie the opportunity to coach in an institution that
is legendary for great coaches, as well as his faith in me tO be directly involved and
responsible for the teaching of students. His advise and willingness to come to my
aid will never be forgotten.

Dr. Margaret Benson deserves many thanks for the development and overseeing
of the trial, as well as her aid in the preparation of numerous articles. Her help will
always be appreciated.

Dr Allen Booren and Dr. Gail Strasburg for their advise regarding the thesis and
their willingness to help is greatly appreciated.

Special thanks are due to Sharon Debar for unending tolerance, instruction, and
patient guidance through the too often perplex laboratory analysis. Without her aid
this thesis would not have been accomplished. To Tom Forton and his crew at the
meat lab I will ever be indebted to for their patience and untiring aid.

I am indebted tO Drs. Mike Allen, Getchen Hill and Steven Rust, as well as their
technicians, Dave Main, Dewey Longuski, and Jane Link for their unselfish use of
their laboratories. In addition, lwould like to thank Drs John Gill and Dennis Banks
for their insight on statistical analysis.

To Shepherd George Good I owe many thanks, not only for his help with the
experiment but also his worldly insight on people and situations will always be

useful. Also, much thanks goes to the sheep barn crew for their aid throughout the
trial.

Sincere gratitude is expressed to Dr. Maynard Hogberg and the Animal Science
Department for financial assistance through an assistantship.

Numerous others have contributed and I am very grateful for their help in the
collection or analysis of data: Dave Allen, Brett Barber, Doug Cook, Tadd Dawson,
Matt Doumit, Josep Garcia, Mark McCully, Daniel Nelson, Roy Radcliff, Janell
Restum, Mike Schelgel, and Dwight Sexton, much thanks.

Most of all I thank those members Of my judging teams who have become good
friends as well as those who have supported and assisted me. Their enthusiasm
and competitiveness has been an inspiration.

I am ever thankful to my parents and family back home in Nebraska for their
ongoing support. I am ever reminded of the attitude they have impressed on me:
That hard work can overcome anything.

TABLE OF CONTENTS

LIST OF TABLES ............................................... vi
LIST OF ABBREVIATIONS ....................................... viii
INTRODUCTION ................................................ 1
LITERATURE REVIEW ........................................... 6
OVERVIEW OF GROWTH ................................... 6
Definition of growth .................................... 6
Measurement of growth ................................. 8

THE ROLE OF ENERGY IN THE FINISHING DIET ................ 8
Overview Of energy in the growing and finishing diet .......... 8

The effect of energy density on carcass composition ......... 12

The effect Of energy density on visceral organ mass ......... 18
ESTIMATION OF BODY COMPOSITION ....................... 19
Linear measurements ................................. 20

Whole body composition and analyses .................... 21

9 - 10 - 11 rib section ................................. 23

Wholesale cuts ...................................... 24

Serial slaughter ...................................... 26

Live animal estimation ................................. 27
OBJECTIVES .................................................. 31
MATERIALS AND METHODS ..................................... 33
RESULTS ..................................................... 45
DISCUSSION .................................................. 74
IMPLICATIONS ................................................ 88
ULAR/AUCAUC ANIMAL USE FORM ............................... 90
LIST OF REFERENCES .......................................... 91

V

Table 1.
Table 2.
Table 3.

Table 4.

Table 5.

Table 6.

Table 7.

Table 8.

Table 9.

Table 10. ~

Table 11.

Table 12.

Table 13.

Table 14.

Table 15.

LIST OF TABLES

Composition Of concentrate diet ......................... 35
Chemical analyses of dietary treatment ................... 37
Effect of dietary treatment on lamb performance ............ 46

Effect Of dietary treatment on total and daily feed intake of

lambs .............................................. 47
Effect Of dietary treatment on slaughter measurements of

lambs .............................................. 49
Effect of dietary treatment on liver, lung, and heart weights

lambs. ............................................. 50
Effect Of dietary treatment on full stomach weights Of lambs . . . 51

Effect of dietary treatment on empty stomach weights of lambs . 52

Effect Of dietary treatment on associated fat Of the gastro-
intestinal tract Of lambs ................................ 53

Effect of dietary treatment on carcass cutability measurements

of lambs ............................................ 55
Effect of dietary treatment on lamb carcass quality traits ...... 56
Effect of dietary treatment on percent carcass composition . . . . 57

Effect of dietary treatment on protein and fatty acid accretion
rates .............................................. 59

Effect of dietary treatment on analyses and composition Of
shoulder cut ........................................ 60

Effect Of dietary treatment on analyses and composition of
leg cut ............................................. 61

vi

Table 16.

Table 17.

Table 18.

Table 19.

Table 20.

Table 21.

Table 22.

Table 23.

Table 24.

Table 25.

Table 26.

Effect of dietary treatment on analyses and composition of
rack cut ............................................ 62

Effect Of dietary treatment on analyses and composition of
loin cut ............................................. 63

Effect Of dietary treatment on analyses and composition Of
breast cut .......................................... 65

Effect of dietary treatment on analyses and composition of
flank cut ............................................ 66

Effect Of dietary treatment on analyses and composition of
shank cut ........................................... 67

Effect Of dietary treatment on analyses and composition Of
neck cut ............................................ 68

Effect of dietary treatment on analyses and composition Of
kidney fat ........................................... 69

Effect Of dietary treatment on performance measurements of
pen trial fed lambs .................................... 71

Effect Of dietary treatment on performance measurements of

pen trial fed lambs .................................... 72
Effect Of dietary treatment on carcass parameters Of pen trial

fed lambs ........................................... 73
Effect Of dietary treatment on breakeven prices of lambs ...... 85

vii

LIST OF ABBREVIATIONS

ADF ........................................... acid detergent fiber
ADG ............................................ average daily gain
ALFA ................................................... alfalfa diet
8 .................................................... body weight
°C ................................................. degree Celsius
cm .................................................... centimeter
CONC ............................................. concentrate diet
CP .................................................. crude protein
d ........................................................... day
DM .................................................... dry matter
DMI .......................................... daily dry matter intake
F I .................................................... feed intake
9 .......................................................... gram
GLM .......................................... General linear model
h .......................................................... hour
kg ...................................................... kilogram
km ...................................................... kilometer
L ........................................................... liter
m ......................................................... meter
Mcal ................................................. megacalorie
NDF ......................................... neutral detergent fibre
SEM ...................................... standard error of the mean
TDN ........................................ total digestible nutrients
wt ........................................................ weight
yr .......................................................... year

viii

INTRODUCTION

The livestock and meat industries have been highly focused on lean animal
growth for the past three decades. Livestock producers have placed considerable
emphasis on reducing the time required for animals to reach a desired market
weight. Rapidly-growing animals generally are biologically and economically more
efficient than their slower-growing contemporaries. Since the late 19605, a high
priority has been placed by the meat animal industry on maximizing lean growth
and limiting excess fat production. Carcass fat has a negative influence on the
amount of lean product in sheep (Carpenter, 1966; Smith et al., 1969; Smith and
Carpenter, 1973). With the development Of the Lean Lamb Certification Program
(USDA, 1989) by the American Sheep Producers Council (ASPC, 1988), a greater
effort has been made by producers to market leaner carcasses. The Lamb
Market Basket Survey (Harris et al., 1990) revealed that primal cuts are being
trimmed to .35 cm of fat to gain consumer acceptability. Excess fat in lamb
carcasses was reported from an intensive national survey by Tatum et al. (1988).
The author evaluated 6,224 head of lambs, from seven major packing plants
across the United States. It was reported that 40 percent Of the lambs surveyed
had yield grades (USDA, 1982) of 4 or higher. This is approximately twice as

many yield grade 4 and 5 carcasses than there were in 1968 and 1971.

2
Carpenter et al. (1968) found 21.3% yield grade 45 and above in 1968. Two

years later, Field at al. (1971) reported a slightly lower proportion of yield grade
4 and 5 carcasses at 19.8%. At the time of Tatum’s et al. (1988) survey only
one-third of the supply of lambs would have met the proposed Lean Lamb
Certification specifications (ASPC, 1988). The American meat producer should
be well aware of the fact that consumers reluctance towards fat has doubled in
the 19803 (NRC, 1988). Because Of this, the American sheep producer can no
longer ignore the fact that they must produce leaner lambs. The concern about
over finished lambs is well documented by Nancy Yanish, a representative for the
Food Marketing Institute, who said, "Retailers, actually supermarket operators,
would rather work with those in the beef industry - who have an over-fat product
but who want to do something about it - than with those in the lamb industry -
who have an over-fat product but who refuse to do anything about it" (Heaton et
al., 1993). Why then has the American sheep producer not responded to the
demand for a leaner product? Producers have not responded to consumer
concerns because it is common practice to price lambs on a guaranteed yield or
dressing percent with seasonal weight docks (Ward and Detten, 1984). When
demand for heavy lambs is high, producers push lambs to heavier weights by
putting on excess fat gain to receive better prices. Packing plants are only
docking lambs that are yield grade 4 and higher which is in excess Of .91 cm (.36
in.) Of 12th rib back fat. This is 2.6 times more fat than the .35 cm that Harris et
al. (1990) reported as a maximum to gain consumer acceptability and .27 cm

higher than that eligible for Lean Lamb Certification. Since over 50% Of the lambs

3

on feed are either owned or contracted to packers, fewer incentives are offered
to private producers for leaner lambs.

In order to survive, producers must take it upon themselves to produce a
carcass that is free of excess fat. Thus, the lamb industry must move more in the
direction Of producing lean, heavy muscled carcasses. The traditional method
to increase lean percent in the carcass of ruminants has been to breed and feed
larger framed, later maturing animals, while still slaughtering them at traditional
weights (Bergen and Merkel, 1991). Baird (1988) reported that lambs that were
larger in their skeletal size in relation to lambs of the same age had lower back
fat measurements. For the livestock production system to obtain a larger mature
body weight animal implies that a larger framed, later maturing cow or ewe is
needed versus an earlier maturing, smaller framed dam. These larger framed
dams will have a greater mature weight and thus require more feed for
maintenance. It has been consistently shown that large framed cows require
more feed and are less efficient than more moderate framed cows (Fox et al.,
1988)

Ruminant nutritionists embarked on extensive research to improve carcass
leanness by reducing the energy level of the diet through alternative feedstuffs or
by reducing daily intake. Much work has been conducted in varying the
concentrate to roughage ratio as well as evaluating alternative roughage sources
(Garret et al., 1960; Osborne et al., 1961; Donefer et al., 1963; Ringkob et al.,
1964; Ray and Mandigo, 1966; Burton and Reed 1969; Glimp, 1971; Craddock

et al., 1974; Rattray et al., 1974; Van Keuren, 1985; Ross et al., 1985; Kinser et

4
al., 1988; Oliverous et al., 1989; Weichenthal et al., 1991; Mader, 1992; Dahlquist

and Mader, 1993). Additionally, studies using feed intake reduced to lower levels
than that Of ad libitum have also been done (Crouse et al., 1978; Fortin et al.,
1980; Fortin et al., 1981; Notter et al., 1984). Reduced intake, however, has not
been a practical approach; even though feed efficiency is increased, average
daily gains tend to decrease. Feeders, however, have found it more profitable to
focus on higher daily gains because, to this date, packers are not rewarding
producers for higher percentages of lean. Many Of the trials varied energy level
in the diet by restricting intake and did not allow animals to consume ad libitum.
Those that did provide ad libitum intakes did not assess carcass composition or
reported conflicting results. Osborne et al., (1961 ) and Ray and Mandigo (1966)
reported that lambs fed low-energy diets had less carcass fat than those fed high-
energy diets when slaughtered at similar weight endpoints. Similar studies by
Ringkob et al. (1964) and Burton and Reid (1969), found that dietary energy
levels did not significantly affect fat content in the carcass. Both trials used lambs
of similar genetic make up and similar body weight endpoints. In a more recent
study, that not only varied the energy composition Of the feedstuffs but also the
level of intake, Crouse et al. (1978) reported that carcass composition was not
affected by dietary treatment; however, internal fat was higher in lambs fed the
high-concentrate diet and thus they had slightly higher yield grades. Because of
the importance Of carcass composition in the market place, as well as conflicting
research reports regarding energy level in diets and its affect on body

composition, this study was designed to evaluate the effects of a high energy diet

5

versus one of a lower energy density on performance and carcass composition
of crossbred feeder lambs. The experimental strategy was to target a heavier
body weight endpoint to better fit the demands Of the industry, which is calling for
producers to market heavier lambs. All lambs would also have ad libitum access
tO the respective diets.

The primary Objective of the study was to examine the effects of energy
content in the diet upon whole carcass composition at a specific weight endpoint

when lambs had ad libitum access to dietary treatments.

LITERATURE REVIEW

Definition of growth

As early as 1911, growth was defined as an increase in the mass of a body
during definite intervals Of time (Schlose, 1911). Hammond (1955) defined growth
as an increase in body weight until maturity is attained. There does not appear
to be a universal agreement on a definition Of growth. Many researchers prefer
the definition proposed by Maynard and Loosli (1969), that true growth is an
increase in muscle, bone, and vital organs and should be distinguished from any
increase in adipose tissue. This definition implies that fattening should be
evaluated separately when studying the production Of meat-producing animals.
Judge at al., (1994) proposed that growth can be defined as a normal process of
increase in size, produced by accretion of tissues similar in composition to those
of the original tissue or organ. Growth can be achieved by one or a combination
of the following processes: 1) hyperplasia, an increase in cell number by cell
division, Characterized by an increase in tissue DNA content which is also a
reflection of nuclei number; (2) hypertrophy, which is an increase in Size of
existing cells, expressed as a ratio Of tissue protein to DNA, which is a measure
of amount of cytoplasm per nucleus; and (3) accretionary growth, which is an

increase in non-cellular structural material (Judge et al., 1994; Grant and

Helferich, 1991).

Growth can be divided into two phases, prenatal and postnatal. Prenatal
growth is accomplished primarily by hyperplasia. Differentiation of tissues,
organs, and systems take place at this time (WIddowson, 1980). Postnatal growth
of individual tissues and vital organs can be represented by a sigmoidal curve of
age versus body weight (Hammond et al., 1983). Various tissues however
develop at different times. An example of this phenomenon is that of muscle and
adipose growth. On a normal plane of nutrition during growth of the animal,
muscle growth exceeds fat accretion. As age and body weight increase, muscle
growth slows and the rate of fat accretion surpasses that Of muscle. The order
Of development of tissue has been Characterized by Hammond (1932) and
McMeekan (1940) to be that of skeleton, muscle, and fat with vital organs being
relatively well developed by the time of birth. The plane and level Of nutrition
greatly affects the growth rates Of organs and tissues (McMeekan, 1940;
Hammond et al., 1983). McMeekan (1940) found that reduced feed intake
delayed maturity of later developing tissues. Additionally, energy intake had a
greater effect on the later developing depot of subcutaneous fat than that of
intermuscular fat. From this he concluded that development of tissues can be
regulated by the level of nutrition provided. He also showed that by altering the
growth curve of the whole body, one may change the body ratio Of lean to fat.
Because Of this, many researchers have studied means Of altering the growth
curve to produce a higher percentage of lean and at the same time achieve an

acceptable rate Of gain to maximize profitability.

Measurement of growth

As noted above, growth has been defined in various ways; consequently,
the preferred measurement of growth will vary among researchers. The
accumulation of total body mass from birth to market or maturity is generally an
accepted means Of measuring growth. Rate of gain is calculated from a specific
starting point to a specific endpoint. Variation of digestive tract fill and body
composition make full weight an imprecise indicator of growth. Thus, shrunk
weight is a preferred method of measuring accrued growth, because it allows for
the subtraction Of apparent digestive tract fill (Tolley et al. 1988). However, full,
shrunk, and empty body weight can change independently of muscle mass and
may not fully reflect a Change in lean mass. Consequently, growth is measured
by some researchers as an increase in lean body mass. This does not take into
account the protein content of vital organs (digestive tract, liver, ect.) which may

increase independently Of carcass lean mass (Carstens et al., 1991 ).

Overview Of Energy in the Growing and Finishing Diet

Consumption of dietary net energy for gain ultimately influences the
composition of meat producing animals (Mersmann, 1991). It has been
established by Searle et al., (1972) and Bergen (1974) that fat gain becomes a
large and constant fraction of weight gain beyond a certain body weight.

Mersmann (1990, 1991) explained how early work by McMeeken (1940), as well

9

as his own (Mersmann, 1987), relates to feeding systems in the United States.
He attributed the use of feeding ad libitum, allowing animals to consume their
desired intake freely, as a common agricultural practice in more developed
countries. The United States has an abundance of relatively low cost grains that
are of high energy value. Which has allowed many feeding operations to be
successful and profitable. The strategy of ad libitum intake generally results in
maximum average daily gain and profitability, when marketing on a live or carcass
weight basis (Smith et al., 1977; Bennet, 1988). Palatability of the product is also
increased due to a higher degree of intramuscular fat. Mersmann (1991) stated
if payment to producers is based on retail product weight, diets that utilize lower
energy densities can reduce carcass fat and increase retail product yield. The
result is an increase in carcass value (Bennet, 1988; Loy et al., 1989) due to a
relative increase in the amount Of lean product. Profit per head, however, may
not necessarily be increased.

Limit feeding has been shown to produce leaner animals (Crouse et al.,
1978; Fortin et al., 1980; Fortin et al., 1981; Whittemore, 1986). In addition to
producing leaner carcasses, restricted intake was conducive to greater gain and
improved feed efficiency (Glimp et al. 1989). Glimp et al., (1989) lambs fed a
90% concentrate diet at 92.5%, ad libitum experienced greater average daily gain
and increased feed efficiency than lambs fed ad libitum (Glimp et al. 1989). This
supports work by Old and Garret (1987), who found that when steers were fed at
85% ad libitum, there was a 20% increase in feed efficiency. When feeding large

numbers Of animals in one pen this method may not be as successful because

10

some animals may consume more than their allocated amount, while others
consume less than desired. Thus, limit feeding is more successful when done
individually (Mersmann, 1991). Limit feeding can be accomplished successfully
by using electronically controlled feeders or individual feeding chutes. Both
systems are expensive to install and, despite being automated, are still labor
intensive. Additionally, slower daily gains and lengthened feeding periods result
in lower turnover of animals within the feeding system, resulting in potentially less
revenue under our current economic structure. Because of these problems,
livestock producers in the United States have not been able to justify
implementing limit feeding programs. Utilizing lower energy feedstuffs, such as
use Of high quality roughage, while still maintaining sufficient average daily gain,
could prove beneficial to cattle feeders as well as lamb producers. Studies done
by Ely et al. (1979) showed that lambs grazing bluegrass-clover pasture plus a
13% crude protein supplement diet had similar gains to lambs fed a concentrate
diet in a dry lot situation. The utilization Of 100% forage diets fed ad libitum has
been well documented in relationship to performance levels (Van Keuran et al,
1969). However, less research has been conducted on the effect Of 100% forage
diets on carcass Characteristics. Roughages are of practical use in sheep diets
because sheep appear more efficient than beef cattle at utilizing forages in
pasture situations (Van Keuran et al., 1969). In a grazing study, Van Keuran et
al. (1969) reported that feeder lambs produced more animal product per hectare
than yearling steers. Parker (1982) and Ely et al. (1979) concluded that even

though average daily gain is reduced, lambs may economically be fed to slaughter

11

on pasture alone. Researchers have recommended that the feeding or grazing
of legumes offers a higher degree of performance than grasses (Marten and
Jordon, 1979; Murphy et al., 1994). Average daily gain was increased because
a greater amount Of net energy was consumed by lambs grazing legumes (Waldo
and Jorgensen, 1981). Additionally, pelleting of forage diets increased feed
intake and average daily gain in studies with feeder lambs (Shain and Stock,
1992). Pelleting diets, however, increased cost per unit of feed.

Tatum et al. (1988) conducted a nationwide survey on sheep feeding and
marketing. They reported that 18% of the lambs surveyed were fed on pasture
while the remainder were fed in feedlots. Lambs had to be on feed from 30 to 60
days and fed on a high concentrate diet prior to slaughter to be Classified as
feedlot lambs (Tatum et al. 1988). Feeding lambs in a feedlot situation enables
the feeder to make the most of his facilities while feeding a varitety of grains. A
rapid turnover of lambs can then be attained thus, resulting in a reduction of fixed
costs and an increase in efficiency. When feeding concentrate feedlot diets,
there is a greater chance that metabolic disorders may occur, possibly resulting
in reduced lamb performance (Krehbiel et al., 1994). Thus, it has been the
common practice in the livestock feeding industry to feed combinations of
concentrates and roughages to prevent feedlot related disorders and to insure
profitability. There are however, differences among data between researchers on

how diets varying in energy affect the lean to fat ratio in carcasses.

12

Effect Of Energy Density on Carcass Composition.

Much work has been done with alternating the nutrient density of the diet,
by varying the concentrate to roughage level, and to study its interrelationships
to growth and body composition in sheep and cattle. Early studies only analyzed
the effect of energy density on overall development of the carcass (Wellington et
al., 1954; Hammond, 1955) and did not study the rate of deposition of fat and
lean. Many researchers (Field at al., 1963; Guenther et al., 1965; Burton and
Reid, 1969; Orskov, 1983) reported that nutritional treatment did not affect body
composition. Field et al. (1963), Winter et al. (1976) and Theriez et al. (1981)
found that age or nutritional treatment did not affect body composition Of lambs
that were Of the same breed and sex, when slaughtered at the same weight
endpoint. Field et al. (1963) fed lambs sired by slow, average, and fast gaining
Southdown rams. Lambs were fed to a constant slaughter weight endpoint of 35
kg. The authors reported that type of birth (single or twin) or age did not affect
carcass composition within each group. The faster gaining rams sired lambs that
gained faster and had a greater percent lean. Winter et al. (1976) fed 35 kg
Corriedale wethers three levels Of energy. The first group was fed continuously
while the second and third groups were fed a energy restricted diet to lose 20%
and 28% Of their body weight before being fed to a constant weight endpoint of
63 kg. Winter et al. (1976) concluded that age or nutritional treatment had no
affect on final body composition when finished lambs were Of the same breed and
sex. Burton and Reid (1969) fed lambs at two different levels of energy and

slaughtered them at both an age and a weight constant endpoint. Both diets were

13

formulated to exceed maintenance requirements for growing lambs. Lambs fed
the lower energy diet took a substantial number of days longer to reach the
desired endweight. The authors concluded upon regression analysis that the
variation in body composition was mostly influenced by carcass weight.
Additionally, Orskov (1983) reported that when lambs were slaughtered at
identical weights, the age at slaughter had little or no effect on Chemical
composition. It was also suggested by MCC. Graham (1982) that the greatest
variability in fat and protein ratios Of the carcass was attributed to carcass weight.
Carcass weight in turn affects the length Of the feeding period. In a study by
Glimp et al. (1989), 298 head of Rambouillet ewes and wether lambs were fed
one Of three diets, varying in the level of energy (55%, 72.5%, or 90%
concentrate). Lambs consuming the high concentrate diets were fed three levels
of intake (ad libitum, 92.5% ad libitum, and 85% ad libitum). Level of concentrate
affected days on feed, average daily gain, feed efficiency, and average daily feed
intake. Lambs consuming the high concentrate diet had the highest, most
desirable, feed efficiency. The poorest feed efficiency was that of the lambs
consuming the low concentrate diet who had the greatest daily feed intake. Yield
grade was unaffected by dietary treatment. Diets varying in energy density have
had dramatic effects on feedlot performance; however, carcass Characteristics
were virtually unaffected in some cases.

Nutritional treatment did affect carcass composition in studies done by Ray

and Mandigo (1966), Searle, MCC. Graham and O’Callaghan (1972), Fortin et al.

13

formulated to exceed maintenance requirements for growing lambs. Lambs fed
the lower energy diet took a substantial number of days longer to reach the
desired endweight. The authors concluded upon regression analysis that the
variation in body composition was mostly influenced by carcass weight.
Additionally, Orskov (1983) reported that when lambs were slaughtered at
identical weights, the age at slaughter had little or no effect on chemical
composition. It was also suggested by MCC. Graham (1982) that the greatest
variability in fat and protein ratios Of the carcass was attributed to carcass weight.
Carcass weight in turn affects the length of the feeding period. In a study by
Glimp et al. (1989), 298 head of Rambouillet ewes and wether lambs were fed
one of three diets, varying in the level of energy (55%, 72.5%, or 90%
concentrate). Lambs consuming the high concentrate diets were fed three levels
Of intake (ad libitum, 92.5% ad libitum, and 85% ad libitum). Level of concentrate
affected days on feed, average daily gain, feed efficiency, and average daily feed
intake. Lambs consuming the high concentrate diet had the highest, most
desirable, feed efficiency. The poorest feed efficiency was that of the lambs
consuming the low concentrate diet who had the greatest daily feed intake. Yield
grade was unaffected by dietary treatment. Diets varying in energy density have
had dramatic effects on feedlot performance; however, carcass characteristics
were virtually unaffected in some cases.

Nutritional treatment did affect carcass composition in studies done by Ray

and Mandigo (1966), Searle, MCC. Graham and O’Callaghan (1972), Fortin et al.

14
(1980 & 1981), Turgeon et al. (1986), Zinn (1987), Mersmann (1991), and Murphy

et al. (1994). Mersmann (1991) stated that if animals are to be raised for lean
muscle mass, they should be fed at less than maximum intake. Searle, MCC.
Grahm, and O’Callaghan (1976) reported that lambs fed diets that produce slower
gains will have a greater proportion of their gain as protein. Additionally, lambs
fed for maximum gain had a greater amount of fat gain. This was also
demonstrated by Fortin et al. (1980, 1981). These authors allowed Angus and
Holstein steers to consume a finishing diet at either ad libitum or 70% ad libitum.
They concluded that cattle consuming greater amounts of energy had higher
percentages of fat and lower percentages of muscle when slaughtered at a
constant carcass weight basis compared to cattle on a lower plane Of nutrition.
The work of Turgeon et al. (1986) studied the effect Of slow versus fast growth
rate on lamb carcass composition. They found that the lambs that experienced
slower growth had similar amounts of protein gain but substantially less fat when
compared to lambs fed for fast growth on a concentrate diet. Mersmann (1991)
suggested that when feeding a balanced diet at restricted energy levels, fat
accretion will be reduced, but muscle deposition will remain at the same rate
providing that energy intake does not drop below maintenance. He based this
suggestion on observations made by Smith et al. (1977), Crouse et al. (1978),
and Whittemore (1986). However, in studies done by Smith et al. (1977), low
energy diets consisted of cattle grazing pasture at ad libitum levels. Thus, animals
may have adjusted for the reduced energy level by consuming more feed

(Mersmann, 1991).

15

In a two-year study, Ray and Mandigo (1966) fed diets varying in energy
level. Lambs were allowed ad libitum intakes of a 70% alfalfa and 30%
concentrate pelleted diet versus a 100% alfalfa pellet diet. The lambs were
slaughtered at similar weight endpoints. The authors reported that lambs
consuming the higher energy diet had a greater fat content as a result of an
increase in subcutaneous fat. The authors reported that weight of kidney fat was
not different. Days on feed was not reported for either treatment. Without days
on feed being reported, and dietary treatments being fed in different calendar
years to different lamb crops, environmental factors may have influenced the data.
Whittemore (1986) showed that as feed intake (kg/d) was reduced, muscle and
fat gains (kg/d) were also reduced. Crouse et al. (1978) fed diets that varied in
energy level and amount to feeder lambs to insure differences in energy intake.
Three diets containing metabolizable energy values Of 2.18, 2.39, and 2.80 Mcal,
respectively, were used and the feeder lambs were slaughtered at four different
weight endpoints Of 32, 42, 54, and 66 kg. Crouse et al. (1978) reported that
although percent of carcass protein decreased slightly (P<.01), as energy density
Of the diet increased, there was little effect on overall carcass composition. Yield
grade (USDA, 1969) was higher for lambs consuming the higher energy diets. On
the present yield grading system (USDA, 1989), however, dietary treatment would
not have affected yield grade because it was reported that 12th rib fat thickness
was unaffected by dietary treatment. Additionally, leg conformation score was not
influenced by dietary treatment (Crouse et al. 1978). Thus, the Change in yield

grade can be attributed to a greater amount of internal fat found in lambs

16

consuming the higher energy density diet.

Guenther et al. (1965) designed an experiment to permit the comparison
Of carcass composition on both an age— and weight-constant basis. In these
studies, Hereford-sired calves were fed at different energy intakes. NO difference
was found in the lean content when the calves were compared on a weight-
constant basis. The research group found significant differences in percentages
of fat within the carcass. Cattle fed on a higher plane Of nutrition had higher
percentages Of fat and lower percentages Of muscle on a carcass weight basis
than did cattle consuming a lower energy level diet. Interestingly, the muscle to
bone ratios in the experiments did not differ among dietary treatments.

More recently, Murphy et al., ( 1994) fed 40 crossbred lambs (20 wethers
and 20 ewes) three dietary treatments. Lambs were slaughtered at a common
endpoint of 42 kg. The two phase experiment (phase I, d 0 to 42; phase II, d 43
to slaughter) examined finishing systems Of grazed alfalfa, 100% concentrate diet
fed drylot, and grazed ryegrass for 42 d followed by the 100% concentrate diet
in drylot. Rotational grazing systems were used for forage management. Alfalfa
and ryegrass paddocks were grazed by lambs for 3 to 4 days. Lambs consuming
the 100% concentrate had greater average daily gains in phase I of the study.
In the second half of the study average daily gain was not different among dietary
treatments. Lambs consuming the 100% concentrate diet had greater average
daily gains over the entire trial than for the lambs that grazed ryegrass the first
42 d. No difference, however, was found for average daily gain between lambs

grazing alfalfa or lambs consuming the 100% concentrate diet. The difference in

17

days on feed was due in part to the wider range of average daily gain in phase
II of the study. Energy intake was not measured in the study and, thus, the
authors made the assumption that differences in average daily gain were due to
differences in the energy density of the feed consumed and total energy intake.
Lambs grazing alfalfa had lower dressing percentages and decreased carcass
weights. Lambs grazing alfalfa also had less total carcass fat with similar
amounts of lean tissue than lambs fed concentrate in both phase I and phase II,
as well as lambs consuming the concentrate diet only in phase II. Daily accretion
rates Of fat were greater for lambs consuming the concentrate diet. No
differences were reported for the daily accretion of protein or bone between lambs
grazing alfalfa or lambs on the 100% concentrate diet. Murphy et al., (1994)
reported that it has been well documented (Rouse et al., 1970) that energy intake
would be deposited in the order Of bone, lean, and fat, until the specific tissue had
reached maximal deposition. Thus, the authors concluded that daily energy
intake for the lambs grazing alfalfa may have been sufficient to meet energy
needed for bone and lean tissue while providing less energy to be partitioned
toward fat accretion. Because of the various suggestions made concerning the
effect Of energy level on carcass composition, further research is needed to allow
a more complete understanding of the relationship of high- and low-energy diets

to carcass development.

18

Effect of Energy Density on Visceral Organ Mass

The mass of visceral components is greatly influenced by nutritional factors
(Murray and Slezacek, 1980; Koong et al., 1983; Ferrell and Koong, 1985).
Nutritional depression can be influenced by the quantity or quality Of feed that the
animal consumes. Nutritional depression results in the inability of an animal to
express its full potential for genetic growth. Animals that do not meet their
nutritional requirments experience reduced growth rate or in severe cases live
weight loss (Hogg, 1991). Most notable losses occur in the liver, gut components,
and intestines (WInter et al., 1976; Ferrell et al., 1986; Burrin et al., 1988). By
increasing dietary bulk, Ferrell et al. ( 1986) as well as Jacobs and Lupton (1984),
reported an increase in the weight Of the large intestine. The researchers
attributed this to hypertrophy Of the intestinal tissue. Conflicting reports have
appeared concerning the effect of dietary bulk on the small intestine. Jacobs
(1983) and Jacobs and White (1983) reported that increasing the level of dietary
fiber increased cell proliferation Of the small intestine. In contrast Goodland and
Wright (1983) showed that an increase in dietary bulk decreased the weight Of the
small intestine. Ferrell et al. (1986) reported that an increase in dietary bulk can
increase the energy requirement of the animal irrespective of energy intake.
Johnson et al. (1985) however, reported as the amount Of roughage in the diet
increased from 10% to 80%, with metabolizable energy intake remaining relatively
constant, there was only a small effect on visceral organ mass. Johnson et al.
(1985) also reported a greater increase in gastrointestinal tracts of cattle fed grass

hay versus alfalfa. In a similar study, Rompala et al. (1988) fed cattle diets

19

containing low to high energy densities. When cattle were slaughtered at the
same weight endpoint, the authors reported greater weights Of the large intestine
and stomach components, while the weight of the small intestine was unaffected.
Drouillard et al. (1991) concluded that results from Burrin (1988) and Rompala et
al. (1988) suggest that the stomach and large intestine are influenced more by
Changes in the amount of bulk consumed in the diet while the small intestine is

more sensitive to the amount of available nutrients.

Estimation of Body Composition

Many researchers have been and are still investigating methods that
accurately estimate body composition. As early as 1893, Iowa State researchers
Wilson and Curtis reported results of performance and carcass traits of cattle in
the Iowa Agricultural Experiment Station Bulletin (Schroeder, 1990). Over the
past hundred years, numerous methods have been proposed and investigated
without much application and yet others (Hankins and Howe, 1946) are still being
utilized today. Valid estimation of carcass composition that is reliable as well as
rapid and simple, is needed to establish the value Of an animal’s carcass. This
estimation needs to be fast and simple, so it can be utilized by packing plants that
process hundreds of amimals per hour. The reliability of this measurement is

economically important, as it will be used not only for sorting carcasses into

20

respective yield groups for processing and fabrication, but also to assess total
product percent. Having a reliable estimate of total carcass value would be true
value based marketing. Currently the pork industry is successfully estimating the
composition of hot carcasses on line with ultrasound (Liu and Stouffer, 1994).
While the beef or lamb industry has yet to perfect this method, researchers
(Zhang, 1994) are making progress. Producers would then have an incentive to
produce a leaner more muscular product. The use of new technologies and past
research data is bringing scientists closer to accurately estimating composition in

an indirect, expedient manner.

Linear measurements

To assess growth, workers (Cook et al., 1951; Kidwell, 1955; Bush at al.,
1969) experimented with various anatomical measurements of live animals.
These measurements were related to weight and skeletal size, but were not
useful in estimating fat content and muscle size. Before studying growth
measurements in live animals, workers measured the depth, width, and
circumference of various locations on the carcasses in an attempt to correlate
these measurements to carcass composition. These researchers realized that by
measuring back fat thickness, as well as length and width Of the longissimus
muscle, a crude estimate of percentage fat and muscle content Of a carcass could
be predicted. Measurements of fat depth and muscle area was first done by

Hirzel (1939), Palson (1939), and McMeekan (1941) in beef, sheep and swine

21

carcasses, respectively. Early studies by these researchers laid the groundwork
for later research to come. Brozek (1961), Zobrisky (1963), Kauffman (1971 ), and
extensive work by Berg and Butterfield (1976), as well as Kempster (1986),
documented that backfat thickness and ribeye area are good indicators of carcass
composition. Rouse et al. (1970) reported that a single linear fat measurement
at the 12th rib medially over the longissimus muscle was the best indicator of total
carcass fat in lambs. Additionally, the area of the longissimus muscle was just
as reliable a predictor of total lean deposition as percent lean in the carcass. All
these measurements are predictors and are not 100% reliable (Topel and
Kauffman, 1988). Thus, the search continues for the ultimate method to predict

carcass composition in live animals.

Whole body composition analyses

Because Of variability found when measuring carcass measurements
subjectively, researchers realized that to effectively and accurately evaluate
nutrition or genetic experiments, whole body composition must be done. Whole
body composition analysis entails the physical dissection and subsequent
Chemical analysis (water, protein, or ether extract) Of all carcass components, or
the grinding of the whole carcass. Jesse et al. (1976) completely dissected beef
carcasses, determined water, protein and fat content and concluded that complete
dissection is an acceptable form of estimating carcass composition when whole

carcass grinding can’t be done. Jesse et al. (1976) findings supported previous

22
research done by Haecker (1914, 1916, 1920) and Trowbridge (1919). There are,

however, disadvantages to using total body composition. Williams et al. (1974)
reported that between researchers and facilities, results on lipid and moisture
content may change. The variability in moisture content is due in part to the
amount of time taken to dissect a cut, as well as environmental effects such as
humidity, and temperature. Thus, Kempster (1984) outlined specific steps for
proper dissection. Another disadvantage of whole body dissection is extremely
high cost. Time and the amount of labor needed to carry out a project having an
adequate number of replications is immense. Cost becomes an important factor,
not only because of labor, but also because of loss of animal product. Because
whole dissection of large animals is cost prohibitive, other methods of estimation
are generally used. However, research done with small animals should utilize
whole dissection methods whenever possible (Schroeder, 1990).

Although whole body composition studies are very reliable to measure
aspects Of protein and fat deposition, the resale value of the carcass is lost. Thus
many workers have experimented with correlating composition Of a specific cut
of meat to that of the whole carcass. The first documented data where
researchers were successful in finding a correlation between wholesale rib and
carcass composition was that of Hall and Emmett (1912). The wholesale rib was
Chosen because of its ease of removal. Other workers (Moulton et al. 1922;
Lush, 1926; Hopper, 1944) also found a good relationship between composition
of the wholesale rib and the carcass. More recently, Moran (1982 and 1983)

found significant variation in wholesale rib composition to carcass composition.

23

In his study, he used animals that had been raised differently since birth and were
Of different genetic make-up. He concluded that fat and protein are not
proportional from carcass to carcass. Therefore equations developed by Hopper
(1944) may need further refinement. Although the use of the wholesale rib has
declined because its removal substantially lowers the value Of the carcass, other

methods have been proposed that utilize only components of the rib.

9-10-11 rib section

Hankins and Howe (1946) conducted an in-depth study comparing the
composition of various cuts of meat within the carcass to that Of the whole
carcass. They found high correlations between the 9—10-11 rib section to the
whole carcass and wholesale rib. Thus the 9-10-11 rib section composition
analysis is frequently often employed to estimate composition Of the whole
carcass. Studies conducted by Jones (1985), Lunt et al. (1985), and Miller et al.
(1988) reported findings that support work by Hankins and Howe (1946) and the
use of the 9-10-11 rib section to be a vaild estimation of carcass composition.
However, other researchers (Berg and Butterfield 1976; Moran, 1982), found it to
be less successful when used on heifers versus steers of the same breed or on
cattle of 805 Indicus breeding. Additionally, Allen (1966) studied carcasses from
two different weight groups (227 to 250 kg and 312 to 340 kg). The author found
the correlations of percent muscle, fat and bone to be lower (.4, .4, and .3, for

muscle, fat, and bone respectively) in heavy versus light carcasses. Thus, fat

24

deposition and muscle growth may not be proportional throughout the carcass
from lighter to heavier weights. However, this may be attributed to the fact that
animals were slaughtered at different physiological ages. There would most likely
be different rates of fat and protein deposition between the two groups (Bergen
and Merkel, 1991). In a more recent study by Nour and Thonney (1994) Holstein
and small framed Angus steers where utilized. It was found that Hankins and
Howe’s (1946) equations slightly over estimated water and protein while
underestimating lipid. This is in agreement with similar results found by Crouse
and Dikeman (1974) and Schroeder (1990). More accurate estimates Of carcass
composition can be found using slightly adjusted equations (Nour and Thonney,
1994). However, Schroeder (1990) pointed out that the 9-10-11 rib section is a
widely accepted method of estimating carcass composition and is relatively cost-
effective. Accurate estimations of carcass composition rely on precise prediction

equafions.

Wholesale cuts

Research has been done correlating the percent yield of various cuts to the
percent yield and composition of the carcass. Early research by Cole et al.
(1960), Hedrick (1968), Miller (1965) Tuma et al. (1967) and more recently by
Hedrick (1983) showed that percent trimmed round was highly correlated to
boneless retail yield of primal cuts as well as the whole carcass. Cole et al.,

(1960) reported that total separable muscle in the carcass could be 90%

25

accounted for by separable muscle in the round. Crouse and Dikeman (1976)
and Rouse et al. (1989) found high correlations for percentage of trimmed round
to percentage of retail product. However, because Of the high percentage of
saleable meat that comes from the round, its use in estimating carcass
composition has not been popular.

The flank is of less monetary value than either the rib or the round and has
proven to be a good indicator Of whole carcass composition (Hankins and Howe,
1946; Allen, 1966; Dikeman, 1968). Hankins and Howe (1946) reported a
correlation between percent fat Of the flank to that Of the carcass of .95, which
was comparable to the 9-10-11 rib section at .93. Additionally, Allen (1966)
reported correlations Of .91 for both percent fat and muscle in the flank to that Of
the carcass. Dikeman (1968), in a study involving wholesale cuts, reported
results similar to those Of Allen (1966). Dikeman (1968) reported that flank
composition had the highest correlation to the amount of fat trim within the
carcass compared to any of the other wholesale cuts. Correlations for
composition were not only the highest for within-weight groups, but also across
weight groups. It was noted that there are variations in flank removal across the
industry. Thus, the wholesale flank may not be a totally reliable indicator Of
carcass composition. In the same study, Dikeman (1968) also found that the
wholesale plate was the second most highly correlated cut to fat yield and percent

retail product.

26

Serial slaughter

Serial slaughter techniques are presently the preferred method for
researchers to map the growth and development of the animal (Anderson, 1988).
Even though serial slaughter techniques are expensive, they are Often used
because methods for assessing composition Of the live animal are still being
tested (Rouse et al., 1992). The group of animals used in the study must be
genetically, as well as phenotypically, similar and raised in the same environment.
Preferably, animals from the same contemporary group, that are of the same size
and genetic potential, should be used. Animals must be similar because they are
slaughtered throughout the trial to plot composition. These animals are assumed
to not only be similar in composition but they are expected to grow and respond
to treatments like the remainder Of the group throughout the trial so that accurate
growth and composition points can be plotted. However, there are some
complications to this method. Extremely large numbers of animals are needed
to give validity to these types of studies. Although animals may be similar,
variation can occur between animals and not be a true representation of all
animals in the study or the cattle population in general (Anderson, 1988).
Methods that may be used to estimate body composition of live animals are

needed. Presently, researchers are attempting to accomplish this goal.

27

Estimating Carcass Charteristics of the Live Animal

Many research reports have discussed the relationship between body
water, body fat and the weight of the fat free body in the animal (Sheng and
Huggins, 1979; Schroeder, 1990). Researchers have experimented with various
dilution techniques and compounds to estimate total body water content in the live
animal. The most Often used tracers are antipyrine, urea, and deuterium oxide
(Schroeder, 1990)

WIddowson (1968) made the assumption that the fat free body is relatively
constant in water, protein and ash (Schroeder, 1990). Thus, when the animal
reaches its chemical maturity, an in vivo measurement of water can be used to
determine composition. The measurement is accomplished by first injecting a
bolus of tracer into the body water of the animal. Blood is then sampled after
equilibration of the tracer in the body pools has occurred. The blood is then
analyzed to determine the concentration of the tracer. Shipley and Clark (1972)
reported that the volume Of fluids (water) can be calculated by dividing amount Of
tracer injected by the concentration of the tracer at the time of equilibration
(Schroeder, 1990).

Antipyrine was used extensively by early researchers (Krabill et al., 1951
and Wellington et al., 1954). However, more precise results were Obtained by
using urea in cattle by Preston and Koch (1973). More recently, Hammond (1984;
1988) suggested that urea dilution is a useful method in determining body
composition and is a relatively quick and simple method. Also, deuterium oxide

(D20) has been used to measure total body water space. Deuterium oxide was

28

first used in humans and extensively studied by Pinson (1952). Much work has
been done in sheep (Till and Downes, 1962; Foot and Greehalgh, 1970; Farrell
and Reardon, 1972; Trigg et al., 1978). These experiments used deuterium oxide
to estimate total body water in an effort to predict body composition. The
reseachers looked at the ruminant water space as one pool, combining both gut
water and empty body water into the total body water pool. The combination of
pools introduced a large degree of error, because water in the digestive tract is
not related to carcass or empty body components (McCarthy, 1981 ). In an effort
to find a more reliable predictor of body water, Byers (1979) developed a
procedure to estimate both gut water and empty body water by using a two-pool
system. Byers (1979) used tracer kinetics, formulated by Shiply and Clark (1972),
to aid in the separation Of the pools. Byers (1979) reported the two-pool system
to be highly correlated (r2=.965) to chemical analysis. The two-pool system was
then successfully used with cattle (Byers, 1979; McCarthy, 1983; Ferrell and
Jenkins, 1984; Miller et al., 1988). In an extensive review by Schroeder (1990),
it was suggested that because of numerous and conflicting results, further studies
need to be conducted on the best experimental procedures for using deuterium
oxide.

Recently, ultrasound has gained popularity, and this approach appears to
have many applications in the livestock industry (Turner et al., 1990; Wilson,
1992). The use Of ultrasonics was first documented by Wild (1950). Other
researchers (Clause, 1957; Panier, 1957; Price et al., 1958) used ultrasound for

estimating carcass composition. Ultrasonics is the act Of passing high-frequency

29

sound signals through tissues. As the sound signals pass through the tissues,
they reflect back when encountering different densities of tissue. These signals
are then transmitted into a visual form by an oscilloscope (Topel, 1988). Through
the use Of real-time ultrasound or B-mode visualization, an accurate,
instantaneous picture of the depth of subcutanous fat as well as an outline of the
loin eye can be produced (Whittaker et al., 1992). It has been documented that
highly trained personnel can accurately predict fat and muscle measurements by
the use of ultrasound (Bass, 1982; Miller et al., 1986; Recio et al., 1986; Robinson
et al., 1992). Extensive research using ultrasound measurements as an indicator
of muscle and fat was reported for sheep (Gooden et al., 1980; Bass, 1982;
Kempster et al., 1982; Cameron and Smith, 1985; Edwards et al., 1989;
Turlington, 1990; Ramsey, 1991), as well as cattle (Smith et al., 1988; Dolezal et
al., 1989; Duello et al., 1990; Houghton et al., 1990; Perry et al., 1990; Cross and
Whittaker, 1992; Rouse et al., 1992). Edwards et al. (1989) studied various
ultrasound measurements to determine composition Of lamb carcasses. The
authors reported that because ultrasonic measurements could not give a
measurement of internal fat it was not a reliable indicator of carcass composition,
and that more accurate ultrasonic measurements were needed. The researchers
(Edwards et al., 1989) concluded that a visual estimation Of body fat by a trained
livestock evaluator is still a preferred the best predictor Of lamb cutability. These
findings were based on the past grading system where kidney, pelvic and heart
(KPH) fat were factors in determining yield grade. Presently, KPH is removed

during the slaughter process before hot carcass weights are taken. The present

30

method Of assigning yield grades in lambs is based solely on 12th rib fat depth
(80993 and Merkel, 1993). Turlington (1990) scanned 160 ram lambs for 12th rib
back fat and then slaughtered them. The author reported acceptable accuracy
in measuring backfat could be obtained. Because lambs were of a narrower
range in fat depth, the accuracy of predicting extremes in fat depth is limited
(Houghton and Turlington, 1992). Ramsey et al., (1991) found that a single
ultrasonic measurement was a better indicator of percent carcass fat than that of
a needle probe at the at the dorsal midline. The workers concluded that the best
indicator Of percentage carcass fat was an ultrasound measurement Of shoulder
fat over the 5th rib. More success has been found in measuring fat and muscle
in cattle (Kempster, 1981; Rouse et al., 1992). More recently, research has
focused on measuring marbling (Brethour, 1990; Zhang, 1994), as well as total
carcass composition and retail value. If this research proves successful, a true
estimation of composition of an animal and its value can be made without

damaging the carcass or the animal’s value (Cross and Whittaker, 1992).

OBJECTIVE

The ever increasing demand by the consumer for leaner meat products has
left sheep producers faced with the problem of marketing leaner lambs that still
grow rapidly and efficiently. Since the 1960’s, the consumer’s pressure on the
meat animal industry has slowed the production Of fat. However, excess fat still
has the most influence on the amount Of saleable product within a carcass (Smith
and Carpenter, 1973). The sheep industry has been notorious for producing
lambs with excess fat. Tatum et al. (1988), in a national survey, reported that
over 40% of the lambs surveyed were yield grade 4 and above. For the sheep
industry to maintain, as well as gain market share, steps must be taken to reduce
the amount of fat on lamb carcasses.

Many Midwestern producers are examining different feeding regimes in an
effort to market leaner carcasses. TO accomplish this, numerous Michigan
producers are feeding 100% alfalfa dehydrated pellets. Many of these producers
have assumed that feeding a 100% forage diet will result in leaner carcasses and
somewhat slower growth with less risk Of lambs going off feed. The present study
was developed to examine effects of energy density in the diet upon total body
composition when lambs have ad libitum access to dietary treatments. This

experimental design would allow maximum average daily gain, but would

31

32

presumably provide a better understanding of the role that a forage diet plays in
reducing fat content of the carcass as well as its effect on visceral organ mass.
The null hypothesis Of the experiment was:
Lambs consuming a 100% forage diet will have (1) a greater average daily
gain, (2) lighter gastrointestinal component weights, and (3) a greater percentage
of carcass lean than lambs fed a concentrate diet when both are slaughtered at

a similar weight endpoint.

MATERIALS AND METHODS

Experiment I - Individually fed lamb feeding study.

Lambs used in this study were selected from the Michigan State University
commercial ewe flock. Thirty-six Suffolk X Dorset X Rambouillet wether lambs
two months of age were used. All lambs were born twin or triplet within a 10-d
period. Siblings were allocated to different dietary treatments. From birth to
weaning, a pelleted creep diet was available to lambs. After lambs were weaned,
the creep diet and alfalfa hay were fed free choice for the two-week period prior
to the start Of the trial. Lambs were vaccinated for enterotoxemia and tetanus at
30 d of age and again at weaning. Lambs were dewormed at weaning and at the
onset Of the trial. Lambs were shorn prior to the initiation of the trial. Initial
weights were taken following a 24-h fast. Six lambs were randomly selected from
the 35 lambs for determination of initial carcass characteristics and composition.

Lambs were assigned to one of two dietary treatments. The high concentrate
(CONC) diet (Table 1) was formulated and processed as a complete pelleted
ration that consisted Of a 75% corn-soybean meal mixture and 25% roughage.
Metabolizable energy (ME) content of the CONC diet was calculated from NRC
(1985) to be 2.79 Mcallkg. The 100% forage (ALFA) diet consisted of 100%

dehydrated alfalfa pellet. The 100% dehydrated alfalfa pellet had a

33

34
metabolizable energy (ME) value (NRC, 1985) of 2.17 Mcallkg for a pellet

containing 17% CP. The dehydrated alfalfa pelleted diet was Obtained from a
commercial source that utilized second and third crop hay. Both diets were
formulated to contain a crude protein content that was in excess of the
requirement for early weaned lambs with moderate growth potential (NRC, 1985),
so that dietary protein would not be a limiting factor in this study.

Table 2 shows the Chemical analysis Of each diet. The CONC diet had a
calculated ME content that was in excess of the NRC requirement for ME of early
weaned lambs with moderate growth potential, whereas the ALFA diet was
calculated to have less than the daily requirement Of ME. Lambs were individually
fed one of the two diets at 12-h intervals. Diets were fed ad libitum amounts
twice daily with orts measured at each feeding. Trace mineral salt, as well as
clean H20, were available at all times. Feedstuffs were collected at weekly
intervals and analyzed for dry matter (DM), crude protein (CP), neutral detergent
fiber (NDF) and acid detergent fiber (ADF) (AOAC. 1984). Total feed, average
daily feed, and ME intakes were determined from individual feed consumed.

Lambs were individually housed in 1.4 x 1.4 m2 pens. Lambs were
weighed every 7 d prior to the am. feeding to monitor weight gain. A final weight
of 52 kg was Chosen as the targeted endpoint of the feeding period. The
endpoint selection was based on the body type and frame size of the lambs in
this study to ensure that a majority of the lambs would reach a quality grade of
Choice and a yield grade 2. As lambs attained the targeted weight endpoint of 52

kg , they were slaughtered 48 h after the weekly weigh date.

35

Table 1. Composition of Concentrate diet

 

 

Item % dry matter
Corn meal 44.88
Dehydrated alfalfa meal 25.50

48 % soybean meal 18.73

Cane molasses 7.3

Pellet binder 1.7
Limestone .55

Dical 18.5 .55
Ammonium Chloride .39

San .39

Vitamin E .06

 

36

Table 2. Chemical analyses Of dietary treatments

 

Dietary treatment

 

 

Item CONC ALFA
Dry matter, % 88 93
Crude protein, % 21.0 17.2
NDF 19.5 40.7
ADF 9.7 25.9
Nem' 1.83 1.34
Neg‘ 1.21 0.77
Metabolizable energy, Mcallkg‘ 2.79 2.17

 

' Calculated from NRC (1985) values.

37

As lambs that attained the final targeted weight were fasted 24 h and transported
to Michigan State University’s meat laboratory. Prior to slaughter, a final shrunk
weight was Obtained. Euthanasia was accomplished through use Of electrical
stimulation. Exsanguination was done by severing the carotid artery and jugular
vein. Following exsanguination, the pelt and head were removed and weighed.
The gastrO-intestinal tract (GIT) and liver were removed, weighed to the nearest
pound and converted to the nearest .1 kg. The GIT was then ligated into the
following components: ruminO-reticulum, omasum, abomasum, small intestine,
and large intestine. After individually weighing each component, contents were
removed and empty weights and weights of dissected fat associated with each
component were recorded. All GIT component weights were measured to the
nearest .1 9. Heart and lung weights were also Obtained and weighed to the
nearest .1 g.

The carcasses were washed and a hot carcass weight was Obtained.
Following a 24-h Chill at 2°C, carcasses were weighed to the nearest .5 kg and
ribbed between the 12th and 13th ribs. Carcass data were collected by trained
university personnel. Backfat was determined by averaging measurements over
the center of the right and left longissimus muscles between the 12th and 13th
ribs. A lower rib fat measurement, taken 4 cm ventral to the longissimus muscle,
was also taken. Areas of the right and left longissimus (ribeye) muscles were
measured using a grid with 20 dots per square inch. Mean longissimus muscle
area was calculated using the measurements Obtained from the right and left

sides. Leg conformation was subjectively evaluated and carcasses were assigned

38

a numerical leg score that corresponded to prime, choice, good, or utility, with
11=Choice°, 12=choice*, etc. (USDA, 1969). Yield grade was determined (USDA,
1989) by the following equation: yield grade = .4 + (10 x average backfat
thickness (inches)). Quality grade was based on a composite evaluation of
conformation, maturity, and quality Of lean flesh. Conformation included an
assessment of overall muscling with emphasis on the greatest development of
muscling in the highest priced primal cuts: leg, loin, rack, and shoulder.
Conformation was assigned a numerical score that corresponded to prime, Choice,
good, or utility grades (17=choice°, 18=Choice*). Maturity, an assessment of the
physiological age of the animal, was determined by an assessment Of the break
joint as well as shape and color of the ribs. Maturity was scored from 1 to 5, with
5 having the surface of the break joint moist, and porous, as well as bright red;
also the ribs would be red. A score of 1 would be progressively less red, with
drier and harder appearing break joints and ribs. Quality Of lean flesh was
evaluated by the quantity of fat streaking on the inside of the flank muscles,
firmness of the lean flesh and external fat. Lambs were assigned a numerical
quality grade that corresponded to prime, choice, good, or utility grade
(17=choice°, 18=choice*) (Boggs and Merkel, 1993).

For compositional analyses, carcasses were halved. Care was taken in
splitting the carcass to ensure minimal deviation from the medial plane Of the
vertebrae. Any deviation from the medial plane was instantly corrected by
repositioning the carcass before proceeding. However, if any unevenly spilt bone

did occur, it was removed from the corresponding side and added to the other

39

side. The carcasses were separated into fore- and hind-saddles between the
12th and 13th ribs. Kidneys and kidney and pelvic fat was removed and weighed.
Percent kidney and pelvic fat was determined by dividing the amount of fat
removed from the abdominal cavity and pelvic area by chilled carcass weight.

Two methods were used to calculate dressing percent. First, dressing
percent was calculated as carcass weight with kidney fat intact because kidney
fat was included in the overall compositional analysis of the carcass. Current
industry standards require kidney fat to be removed at slaughter before hot
carcass weight is Obtained. Thus, a dressing percent with kidney and pelvic fat
removed from the carcass was also calculated. The right side Of the carcass was
fabricated into wholesale, retail, and miscellaneous cuts, according to the National
Association of Meat Purveyors buyers guide (NAMP, 1992) and used to determine
yields and compositional analyses. The following cuts were fabricated: square
cut four-rib shoulder, neck removed; eight-rib rack; one-rib loin; leg; foreshank;
breast; and miscellaneous cuts (flank, neck, kidney and pelvic, fat). The cuts
were vacuumed packed and stored at -25° C. The left side Of the carcass was
marketed through Michigan State University meats lab to compensate for lamb
cost

Cuts were thawed at 4°C for 24 to 36 h. Cuts were weighed and separated
into tissue and bone. Bones were dissected completely free of muscle, fat,
tendons, and ligaments, but not cartilage. Tissue weights were recorded for each
cut. Soft tissue was then ground three times through a .5 cm plate and mixed

thoroughly by hand between grindings to assure a representative sample was

4O

taken. A 400 to 500 9 sample was collected and stored in a whirl-pac bag at -30°
C until further preparation. Samples were thoroughly homogenized in 1 to 2 l of
liquid nitrogen in a Waring blender until a powdered substance was obtained.
Powdered samples were placed in whirl-pac bags and left open in a -30°C cooler
for 24 h to allow carbon dioxide sublimation prior to sealing. After sealing,
samples were stored at -30°C until analyses.

Duplicate samples were analyzed for dry matter (DM), protein and ether
extract. One- to 2- 9 samples were measured into dried aluminum pans and dried
at 60°C for approximately 15 to 18 h. Weight loss was recorded after cooling the
samples in a desiccator and dry matter was calculated (AOAC, 1984). Dried
samples were stored for ether extract determination in a dry room at 46°C.
Duplicate samples were analyzed for fat content for 12-h in a Soxhlet apparatus
followed by a 12 h evaporation period. Samples were then dried at 60°C for 12
h before reweighing, and fat content was calculated (AOAC, 1984). Crude
protein Of duplicate samples was calculated from total nitrogen. Total nitrogen
(Kjeldahl) was determined using a Technicon auto-analyzer system (AOAC,
1984). Samples weighing 1 to 2 g were analyzed. Analyses Of DM, ether
extract, and nitrogen samples were repeated until a difference Of less than 1.5 %
from the mean was obtained. Percentage DM, protein and fat were used to
determine the total composition of each cut.

TO calculate accretion rates Of protein and fat, equations were adopted

from Anderson et al. (1988). The equation adopted is as follows:

a = ((bC) - (dam/9

41

where:
a = estimated accretion rate of carcass fat or protein (g/d) for a particular lamb
b = carcass weight (g)
c = estimated carcass fat or protein (%)
d = initial live weight (g)
e = average dressing percentage of initial slaughter group
f = initial estimated carcass protein or fat (%)
g = number of days on feed
Data were analyzed using analysis of variance, with diet as the main effect.
Analysis was performed using General Linear Models of SAS (SAS, 1987).
Differences between diets were tested using Bonferroni t test. Least square
means and standard errors are presented in the tables that follow. The ANOVA
model for the trial was as follows: Yij = u + Ti + E”.
where: Yii = Variable being measured ( i.e., performance & carcass data).
u = Overall mean.
Ti = Effect Of treatment (ALFA or CONC).

Eij = Experimental Error.

Experiment Il - Group-fed lamb feeding study.
Lambs used in this study were ofspring selected from the Michigan State
University commercial ewe flock. Forty-eight Suffolk X Dorset X Rambouillet

wether lambs 2 mo of age were used. All lambs were born within a 10-d period

42

of each other. From birth to weaning, lambs were fed a pelleted creep ration.
Lambs were weaned at 60 d of age. The pelleted creep diet and alfalfa hay were
fed free Choice for 2 wk prior to the start Of the trial. Lambs were vaccinated for
enterotoxemia and tetanus at 30 d of age and again at weaning. Lambs were
wormed at weaning and at the onset of the trial. Lambs were shorn prior to the
initiation of the trial. Initial weights were taken following a 24-h fast.

Lambs were blocked by weight and randomly assigned to one of two dietary
treatments. Six weight blocks with eight lambs/block and four lambs/pen were
randomly assigned to pen. The high concentrate (CONC) diet (Table 1) was
formulated and processed as a complete pelleted ration that consisted Of a 75%
corn-soybean meal mixture and 25% roughage. The ME content Of the CONC
diet was calculated from NRC (1985) feed values to be 2.79 Mcallkg (NRC, 1985).
A 100% forage (ALFA) diet consisted of 100% dehydrated alfalfa pellet. The
100% pellet had a NRC (1985) book value of 2.17 Mcal ME/kg for a pellet
containing 17% crude protein. The dehydrated alfalfa pelleted diet was obtained
from a commercial source that utilized second and third crop hay. Both diets
were formulated to have a CP content in excess of the requirement for early
weaned lambs with moderate growth potential (NRC, 1985) so that dietary protein
would not be a limiting factor in this study. Table 2 shows the chemical analysis
Of each diet. The CONC diet had a calculated ME content that was in excess Of
the NRC (1985) requirement for ME of early weaned lambs with moderate growth
potential, whereas the ALFA diet was calculated to have less than the daily

requirement of ME. Diets were fed ad libitum amounts twice daily with orts

43

measured at each feeding. Lambs were fed at 12-h intervals at 6:00 AM. and
PM. Trace mineral salt, as well as clean water, was available free Choice at all
times. Feedstuffs were collected at weekly intervals and analyzed for DM, CP,
NDF and ADF (AOAC. 1984).

Four lambs per group were penned in 3.7 x 1.8 m2 pens. Lambs were
weighed every 7 d prior to the AM. feeding to monitor weight gain. A final weight
of 52 kg was Chosen as the targeted weight endpoint. This was based on the
body type and frame size of the lambs in this study to ensure that a majority of
the lambs would reach a quality grade of choice and a yield grade of 2.

Lambs were slaughtered in two groups. Both groups were slaughtered at
the targeted weight endpoint of 52 kg. Lambs that had attained final weight were
transported 106 km to Wolverine Packing, Detroit, Michigan. Euthanasia was
accomplished through use Of electrical stimulation. Exsanguination was done by
severing the carotid artery and jugular vein. Following exsanguination, the pelt
and head were removed. The GIT was removed followed by removal of the
kidneys and kidney and pelvic fat from the carcass. These Operations were
accomplished by trained personnel manually removing the fat. The carcass was
then washed and a hot carcass weight was Obtained. Kidneys and kidney and
pelvic fat were bagged and identified after removal from the carcass. The sample
was transported back to Michigan State University where they were allowed to
Chill at 4°C. Kidneys were then removed from fat and kidney and pelvic fat was
weighed to the nearest .1 9. Following a 24-h chill at 2°C, lamb carcasses were

ribbed between the 12th and 13th ribs. Carcass data were collected by trained

44

university personnel. Average backfat was measured over the center of the right
and left longissimus muscle between the 12th and 13th ribs. Areas of the right
and left longissimus muscles were measured using a grid with 20 dots / square
inch. Mean longissimus muscle area was calculated using the measurements
obtained from the right and left sides. Leg conformation was subjectively
evaluated and carcasses were assigned a numerical score that corresponded to
prime, choice, good, or utility, with 11=choice°, 12=choice*, etc. (USDA, 1969).
Yield grade was determined (USDA, 1989) by the following equation: yield grade
= .4 + (10 x average backfat thickness (inches)). Quality grade was based on a
composite evaluation Of conformation, maturity, and quality of lean flesh. Lambs
were assigned a numerical quality grade that corresponded to prime, Choice,
good, or utility grades (17=choice°, 18=choice”).

Data were analyzed by analysis of variance with diet as the main effect.
Analysis was performed using General Linear Models Of SAS (SAS, 1987). Least
square means and standard errors are presented in the tables. The interaction
of treatment and block was used as error term for each varrible measured. The
ANOVA model for the trial was as follows: Yijk = u + Ti + Bj + TxBixj + Eijk

where: Yijk = the varrible measured.

u = Overall mean.

Ti= Diet (main effect).

Bj = Pen

TxBixj = Interaction of treatment and block.

Eijk = Experimental Error.

RESULTS

Experiment I - Individually fed lamb feeding study.

Feedlot performance for each dietary treatment, CONC and ALFA, is
shown in Table 3. Mean starting weights of lambs were the same; 30.5 kg for
CONC-fed lambs and 30.6 kg for ALFA-fed lambs. There was no difference in
mean final weight of lambs off-test, since lams were slaughtered at a constant
weight endpoint. Thus, total live weight gain was not impacted by treatment;
however, as time on feed increased, ADG decreased. Concentrate-fed lambs
required 10 fewer days (P<.05) to reach the targeted weight endpoint of 52 kg
than lambs fed the ALFA diet (Table 3). Average daily gains of lambs were
higher (P<.01) for CONC at 425 g/d than ALFA fed lambs at 344 gld. Feed
efficiency, expressed as live animal gain per kg of feed, favored the CONC-fed
lambs (Table 3).

Both daily and total dry matter feed intakes on are shown in Table 4.
ALFA-fed lambs consumed more (P<.01) dry matter, both on a daily basis and
over the duration of the trial. Metabolizable energy intakes were similar on a daily
basis, and for the duration Of the trial. Results of slaughter data between dietary
treatments are given in Table 5. Because lambs were slaughtered at a constant

weight endpoint no differences were found between treatments for slaughter

45

46

Table 3. Effect of dietary treatment on lamb performance

 

 

 

Dietary treatment
Item CONC SEM ALFA SEM P
Initial wt, kg 30.5 .70 30.6 .70 .94
Final wt, kg‘I 52.4 .30 51.8 .30 .19
Gain, kg 21.9 .70 21.3 .70 .53
Days on feed 53 3.0 63 3.0 .04
ADG, gld 425 15 344 16 .001
Gain/feed, kg/kg .26 .01 .18 .01 .0001

 

' Final wt was measured after a 24 h fasting period.
" Feed efficiency is expressed as kg gain I kg feed intake.

47

Table 4. Effect Of dietary treatment on total and daily feed intake of lambs

 

Dietary treatment

 

 

 

Item CONC SEM ALFA SEM P
Total intake
As fed, kg 100.8 6.2 133.4 6.5 .001
Dry matter, kg 86.2 5.6 124.0 5.8 .0001
ME, Mcal‘ 247.5 13.7 268.9 14.1 .29
Avgage daily intake
As fed, kg 1.91 .02 2.11 .03 .0001
Dry matter, kg 1.64 .02 1.96 .02 .0001
ME, Mcal‘ 4.89 .32 4.35 .33 .25

 

‘ Metabolizeable energy content of feed was calculated from NRC (1985)
values.

48

weight when expressed as a shrunk live weight prior to slaughter. Hot carcass
weights were not affected by treatment. When expressing Chilled carcass weight
with the kidney and pelvic fat as a component of the carcass, CONC-fed lambs
had significantly heavier carcasses (P<.05). Thus, dressing percentage was
greater (P<.07) for CONC-fed lambs.

Weights for liver, lungs and heart are shown in Table 6. Lambs consuming
the ALFA diet had heavier (P<.05) liver weights. NO differences were found for
lung and heart weights between dietary treatments. Table 7 presents full
(including digesta) weight of the components Of the GIT. The omasum, and small
and large intestine weights were heavier (P<.01) for ALFA. Full weights (FVV) for
rumino-reticulum and abomasum were unaffected by dietary treatment. Empty
weights of the GIT and corresponding components,shown in Table 8, followed
the pattern of gut component weights including contents. There were no
differences between ruminO-reticulum or abomasum empty weights. Mean empty
weight Of GIT was heavier (P<.01) in ALFA fed lambs. Likewise, omasum (P<.01)
and small and large intestine empty weights were greater (P<.05) for ALFA-fed
lambs.

Fat associated with the whole GIT, as well as separate GIT components,
is shown in Table 9. Visceral fat associated with the rumino-reticulum, omasum,
abomasum, small intestine and large intestine was similar amoung lambs from
both treatments. Omental fat expressed as the sum of the rumino-reticulum,
omasum and abomasum was also similar. Collectively, the total amount of fat

associated with GIT was similar (1.6 kg) for lambs on both treatments, which is

49

Table 5. Effect Of dietary treatment on slaughter measurements of lambs

 

Dietary treatment

 

 

Item CONC SEM ALFA SEM P

Slaughter wt, kg 49.4 .5 48.8 .5 .40
Hot carcass wt, kg 26.5 .4 25.6 .4 .10
Chilled carcass wt, kg 26.2 .3 25.2 .3 .04
Dressing %' 53.1 .5 51.7 .5 .07
Dressing %'° 52.0 .5 50.5 .5 .05

 

' Dressing percent calculated with kidney and pelvic fat within the carcass.
b Dressing percent calculated with kidney and pelvic fat removed from the

carcass.

Table 6. Effect of dietary treatment on liver, lung and heart weights of

50

 

 

 

lambs
Dietary treatment
Item CONC SEM ALFA SEM P
Liver, 9 922.9 18.8 986.6 18.8 .02
Lungs, 9 803.7 27.3 768.6 28.3 .38
Heart, 9 378.9 11.9 376.7 12.3 .90

 

51

Table 7. Effect of dietary treatment on full stomach weights of lambs

 

Dietary treatment

 

 

Item CONC SEM ALFA SEM P
RuminO-reticulum, 9 5230.4 309.9 5426.3 320.8 .66
Omasum, 9 228.6 11.5 298.9 11.9 .0002
Abomasum, 9 604.6 42.7 569.9 44.2 .58
Small intestine, 9 1698.4 54.7 1992.7 56.6 .001
Large intestine, 9 12240 289 1 3095 299 .05

 

Table 8. Effect of dietary treatment on empty stomach weights of lambs

52

 

 

 

Dietary treatment

Item CONC SEM ALFA SEM P
RuminO-reticulum, 9 893.1 24.8 958.7 25.7 .08
Omasum, 9 110.7 5.8 137.7 6.0 .003
Abomasum, 9 181.4 8.1 178.4 8.4 .80
Small intestine, 9 852.9 31.7 976.4 32.8 .02
Large intestine, 9 417.7 23.0 488.9 23.8 .04
Gasto-intestinal tract, 9 2455.7 66.5 2740.1 68.8 .01

 

53

Table 9. Effect of dietary treatment on associated fat of the gastrO-intestinal tract

 

 

 

of lambs
Dietary treatment

Item CONC SEM ALFA SEM P

RuminO-reticulum, 9 693.4 65.7 782.9 68.0 .35
Omasum, g 19.5 3.4 23.6 3.4 .42
Abomasum, 9 126.0 12.0 127.7 11.7 .93
Omental, g‘I 835.3 39.7 892.1 41.2 .60
Small intestine, 9 427.3 25.1 478.1 26.0 .17
Large intestine, 9 256.6 16.1 265.1 16.7 .72
GastrO-intestinal tract, 9 1538.5 88.7 1642.6 92.4 .42

 

'Sum of fat associated with the ruminO-reticulm, omasum and abomasum.

54

approximately 3% of the body weight of the lambs.

Carcass cutability measurements summarized by dietary treatment are shown
in Table 10. NO differences were found between treatments for backfat thickness,
lower rib fat and yield grade. Ribeye area and leg conformation score were also
similar. Total amount of kidney and pelvic fat removed from the carcasses as well
as the percentage Of kidney and pelvic fat in the carcasses were similar across
dietary treatments.

Quality parameters were not affected by dietary treatment as shown in Table
11. Flank streaking, lean color, rib color and conformation scores were the same
between treatments. Thus, quality grades between CONC and ALFA-fed diets
were not different.

Percentages Of fat, protein, bone, and water in carcasses are given in Table
12. When expressing the amount Of fat and protein as a percentage of carcass
weight, no differences were found between dietary treatments.

Daily accretion rates of fat, protein, bone and water are presented in Table 13.
Total grams of fat deposited within the carcass on a daily basis were greater
(P<.05) for CONC-fed lambs. Lambs consuming the CONC diet also deposited
greater (P<.05) amounts Of protein than ALFA-fed lambs. Greater amounts of
water were deposited per d for the CONC than for the ALFA-fed lambs. Thus,
lambs consuming the CONC diet had greater (P<.01) rates of total carcass gain
than the ALFA-fed lambs. When expressing daily accretion as a ratio of the kg

Of fat deposited per kg of protein, no difference was found between treatments.

55

Table 10. Effect of dietary treatment on carcass cutability measurements

Of lambs

 

Dietary treatment

 

 

Item CONC SEM ALFA SEM P

Backfat thickness, cm .38 .04 .46 .05 .17
Lower rib fat thickness, cm 1 .21 .10 1 .17 .10 .77
Yield grade 1.89 .17 2.24 .18 .17
Ribeye area, cm2 15.4 .5 14.1 .5 .07
Leg score 12.0 .1 11.8 .1 .25
Total kidney fat, 9 560.0 52.4 566.0 54.2 .94
Total kidney fat, % ccw 2.10 .18 2.24 .19 .61

 

" 10 = choice' ; 11= choice° ; 12 = Choice“.

56

Table 11. Effect of dietary treatment on quality Characteristics of lamb carcasses

 

Dietary treatment

 

 

Item CONC SEM ALFA SEM P

Flank streakinga 3.20 .17 3.14 .18 .82
Lean color“ 3.20 .15 3.21 .15 .95
Rib color‘ 3.27 .18 3.29 .19 .94
Conformationb 12.00 .13 1 1.79 .13 .25
Quality gradec 17.93 .07 18.07 .07 .17

 

‘ 1 = least desirable; 5 = most desirable.
” 10 = Choice‘; 11 = choice° ; 12 = choice *.
° 17 = choice“ ; 18 = choice° ; 19 = Choice *.

57

Table 12. Effect Of dietary treatment on percent composition of removed carcass

 

 

 

fissue
Dietary treatment
Item CONC SEM ALFA SEM P
Fat, % 22.23 .92 22.37 .95 .92
Protein, % 11.63 .16 11.53 .16 .67
Moisture, % 48.20 .51 48.04 .53 .83

Bone, % 17.93 .44 18.06 .45 .84

 

58

Nine cuts were analyzed to determine composition of the carcass. Each cut’s
bone-in and boneless tissue weight is recored. Boneless tissue was individually
analyzed for DM, fat, and protein. Total composition of the cut was then
calculated and reported in each table. Values for shoulder and leg weights are
shown in Table 14 and 15, respectively. Concentrate-fed lambs had heavier
(P<.01) shoulder cut weights than ALFA-fed lambs. Boneless tissue weights were
heavier (P<.01) for CONC-fed lambs. Chemical analyses for DM, fat and protein
of shoulder tissue did not differ between dietary treatment. When expressing the
total composition Of the cut, dietary treatment had no effect on the proportions of
fat, protein, bone, or water within each cut.

Effect Of dietary treatment on the leg cut (Table 15) was similar to results of the
shoulder cut. Dietary treatment affected leg cut weight as well as boneless tissue
weight. Concentrate-fed lambs had 3.5 % heavier (P<.05) leg cut weights than
ALFA-fed lambs. Boneless tissue weights were 4.0 % heavier (P<.01) for CONC-
fed lambs. Dietary treatment did not affect chemical analyses of boneless tissue
for DM, fat, or protein. Treatment had no effect on the percentage of fat, protein,
bone or water found in the leg cut.

Values for the rack and loin are shown in tables 16 and 17, respectively.
Concentrate-fed lambs tended to have heavier (P<.10) cut weights for both the
rack and loin.; however, boneless tissue weights for each cut were unaffected by
treatment. Chemical analyses of boneless tissue of the seperate cuts, as well as

composition of those cuts, were not affected by dietary treatment.

Table 13. Effect of dietary treatment on daily tissue daily accreation rates

59

 

Dietary treatment

 

 

Item CONC SEM ALFA SEM P
Fat, 9 75.6 4.2 59.5 4.4 .01
Protein, 9 22.8 1.1 16.4 1.1 .0003
Bone, g 17.1 1.9 10.7 2.0 .03
Moisture, g 91.7 4.2 66.7 4.3 .0003
Carcass gain,g 207.5 7.0 157.0 7.3 .0001
Fat / protein 3.35 .27 3.84 .28 .222
Days on Feed 53 3.0 63 3.0 .04

 

60

Table 14. Effect of diet on composition of shoulder cut

 

Dietary treatment

 

 

 

 

Item CONC SEM ALFA SEM P
Shoulder cut wt, kg 2.87 .05 2.64 .05 .01
Boneless shoulder cut tissue wt, kg 2.35 .03 2.18 .03 .002
% dry matter, boneless tissue 39.8 .7 38.9 .7 .34
Analysis of boneless tissue. DM

% fat 59.9 1.1 59.5 1.1 .81

% protein 35.5 1.1 36.7 1.1 .46
Commition of shoulder cuL_fresh basis

% fat 19.6 .7 19.2 .7 .68

% protein 11.5 .2 11.7 .2 .58

% water 49.4 .7 50.5 .7 .23

% bone 16.6 .5 16.7 .5 .86

 

Table 15. Effect of diet on composition of leg cut

61

 

Dietary treatment

 

 

 

 

 

Item CONC SEM ALFA SEM P
Leg cut wt, kg 4.00 .04 3.86 .04 .02
Boneless leg cut tissue wt, kg 3.23 .04 3.08 .04 .01
% dry matter 34.3 .6 35.3 .6 .25
Analysis of boneless tissue. DM

% fat 47.1 1.4 48.2 1.5 .58

% protein 47.0 1.3 45.4 1.3 .38
Composition of leg cut. wet ba_i_s

% fat 13.1 .7 13.7 .7 .52

% protein 13.0 .2 12.7 .2 .34

% water 53.0 .5 51.7 .5 .05

% bone 19.3 .3 19.6 .3 .54

 

62

Table 16. Effect of diet on composition of rack cut

 

Dietary treatment

 

Item CONC SEM ALFA SEM

 

 

Rack cut wt, kg 1.46 .04 1.34 .04
Boneless rack cut tissue wt, kg 1.19 .04 1.11 .04
% dry matter 49.6 1.2 5.5 1.2
Analysis of boneless tissue, DM

% fat 71.9 1.3 72.7 1.3

% protein 25.0 1.2 24.0 1.2
Commsition of rack cut. wet bai

% fat 29.2 1.4 30.3 1.5

% protein 10.0 9.7

% water 40.8 40.2

% bone 18.0 16.9 .8

.07
.14
.61

.66
.58

.59
.37
.57
.33

 

Table 17. Effect of diet on composition of loin cut

63

 

Dietary treatment

 

 

 

 

Item CONC SEM ALFA SEM P
Loin cut wt, kg 1.40 .05 1.28 .05 .08
Boneless loin cut tissue wt, kg 1.15 .04 1.08 .04 .17
% dry matter, boneless tissue 44.6 1.0 45.2 1.0 .65
An_a__lvsis of boneless tissue. DM

% fat 64.8 1.6 65.4 1.7 .81

% protein 32.0 1.4 31.5 1.4 .79
Composition of loin cut. wet Eris

% fat 24.1 1.3 25.4 1.4 .51

% protein 11.8 .3 11.7 .3 .92

% water 45.8 1.0 46.1 1.1 .86

% bone 14.3 .9 14.9 .9 .64

 

64

Tables 18,19, 20, 21, and 22 present cut weights and boneless cut weights, as
well as Chemical analyses Of the boneless tissue and composition of each cut for
breast, flank, shank, neck, and kidney fat, respectively. Dietary treatment had no
effect on cut or boneless cut weights Of these cuts. Chemical analysis of each
cut was unaffected by dietary treatment. Additionally, the proportion of fat,

protein, bone, and water in each cut was unaffected by diet.

65

Table 18. Effect of diet on composition of breast cut

 

 

 

 

 

Dietary treatment

Item CONC 8 EM ALFA SEM P
Breast cut wt, kg 1.17 .05 1.20 .06 .77
Boneless breast cut tissue wt, kg .97 .04 .96 .04 .96
% dry matter 49.9 .9 49.7 1.0 .88
Analysis of boneless tissue. DM

% fat 74.3 1.0 73.8 1.1 .75

% protein 23.3 .9 23.4 1.0 .96
Mosition of breast cut, Wm

% fat 30.7 1.1 29.8 1.1 .58

% protein 9.5 .23 9.3 .24 .66

% water 41.3 40.7 .64

% bone 16.9 .8 17.3 .8 .70

 

Table 19. Effect of diet on composition of flank cut

66

 

Dietary treatment

 

 

 

 

Item CONC SEM ALFA SEM P
Flank cut wt, kg .489 .020 .474 .021 .63
Boneless flank cut tissue wt, kg .488 .020 .474 .021 .62
% dry matter 48.71 1.17 46.69 1.22 .24
Analysis olyneless tissue, DM

% fat 71.48 1.52 69.05 1.57 .28

% protein 25.95 1.34 27.96 1.41 .31
Composition of flank cut, wet basis

% fat 35.1 1.5 32.4 1.6 .23

% protein 12.4 .4 12.9 .4 .40

% water 51.2 1.2 53.2 1.2 .25

% bone 0 0 0 0 0

 

67

Table 20. Effect of diet on composition of shank cut

 

 

 

 

 

 

 

Dietary treatment

Item CONC SEM ALFA SEM P
Shank cut wt, kg .533 .01 .523 .01 .54
Boneless shank cut tissue wt, kg .332 .01 .324 .01 .59
% dry matter 32.8 .5 32.9 .5 .94
Analvsis of boneless tissue DM

% fat 41.5 1.6 42.4 1.6 .70

"/0 protein 53.5 1.5 51.0 1.6 .25
Composition of shank cut. wet ba_sig

% fat 8.6 5 8.7 .86

% protein 10.9 10.3 .15

% water 41.7 .6 41.5 .7 .78

% bone 37.6 1.1 37.6 1.1 .97

 

Table 21. Effect of diet on composition of neck cut

68

 

 

 

 

 

Dietary treatment

Item CONC S EM ALFA SEM P
Neck cut wt, kg .390 .01 .370 .01 .28
Boneless neck cut tissue wt, kg” .286 .01 .274 .01 .37
% dry matter 39.7 1.1 39.6 1.1 .94
Analysis of boneless tissue. DM

% fat 60.1 1.6 57.0 1.6 .19

% protein 37.3 1.3 38.4 1.4 .59
Composition of neck cut. wet ba_sis

% fat 17.7 1.0 16.9 1.0 .58

% protein 10.8 .4 11.1 .4 .55

% water 44.3 .84 44.5 .87 .85

% bone 24.8 1.3 24.6 1.4 .90

 

69

Table 22. Effect of diet composition of kidney fat

 

Dietary treatment

 

 

 

Item CONC SEM ALFA SEM P
Kidney fat cut wt, kg .297 .027 .285 .028 .76
Boneless kidney fat cut tissue wt, kg .297 .027 .285 .028 .76
% dry matter 84.1 1.1 82.3 1.1 .27
Analysis of boneless tissue, DM

% fat 97.6 97.2 .23

% protein 2.7 .2 2.9 .2 .42
Commition of kidney fat cut, wet basis

% fat 82.1 1.2 80.2 1.2 .24

% protein 2.3 .2 2.4 .2 .53

% water 15.9 1.1 17.6 1.1 .27

% bone 0 0 0 0 0

 

7O

Experiment ll-Group fed lamb feeding study.

Performance data for dietary treatments, CONC and ALFA, are shown in Table
23. Starting weights of lambs were identical at 26.1 kg for lambs in each of the
treatments. No differences were found for final weight of lambs Off-test as lambs
were slaughtered at a constant weight endpoint. Thus, total live weight gain was
not affected by treatment. Alfalfa-fed lambs reached the final slaughter weight at
81.0 d versus 78.6 d for the CONC. However, neither days on feed nor ADG
were affected by dietary treatment.

Total and daily feed intakes are presented in Table 24. Intakes are expressed
on a per lamb basis calculated from the average intake per lamb per pen. ALFA-
fed lambs consumed more (P<.01) feed, both on a daily basis and for the entire
trial. When expressing intake on a DM basis, ALFA lambs consumed more
(P<.01) feed for the whole trial and on a daily basis.

Differences between dietary treatment for carcass measurements are shown
in Table 25. Hot carcass weights were heavier (P<.05) for CONC than for ALFA-
fed lambs. Dressing percentage, when calculated using hot carcass weight with
kidney and pelvic fat removed, was greater (P<.05) for CONC-fed lambs. Ribeye
area and leg conformation score were unaffected by dietary treatment. Dietary
treatment did not affect backfat but yield grade was shown to be lower (P<.05) for
ALFA-fed lambs even though they differed only .01 of a yield grade. Diet had no
effect on the weight of kidney and pelvic fat of each carcass. Quality grade of

lambs was not affected by dietary treatment.

71

Table 23. Effect of dietary treatment on performance measurements of lambs
group fed in pens

 

Dietary treatment

 

 

Item CONC SEM ALFA SEM P

Initial wt, kg 26.13 .06 26.11 .07 .97
Final wt, kg 50.50 .48 50.19 .52 .76
Gain, kg 24.36 .48 24.07 .52 .71
Days on feed 78.6 1.6 81.0 1.8 .38

Avg daily gain, g/d 310 8 298 9 .41

72

Table 24. Effect of dietary treatment on total and daily feed intakes of goup

 

 

 

 

fed lambs’I
Dietary treatment
Item CONC SEM ALFA SEM P
Total intake
As fed, kg 135.7 3.5 169.7 3.5 .0001
Dry matter, kg 119.4 3.2 157.8 3.2 .0001
ME, Mcal" 333.1 7.9 342.5 7.9 .41
Averagfi dam intafi
As fed, kg 1.73 .04 2.11 .04 .0001
Dry matter, kg 1.52 .04 2.0 .04 .0001
ME, Mcalb 4.25 .09 4.2 .09 .98
Feed efficiency" .18 .004 .14 .004 .0001

 

‘ Values expressed per individual lamb represent a pen average of 4 lambs.

b Metabolizeable energy content Of feed was calculated by from NRC(1987)
book values.

° Feed efficiency is expressed as kg gain / kg feed intake.

73

Table 25. Effect Of dietary treatment on carcass Characteristics of group fed

lambs

 

Item

Dietary treatment

 

CONC SEM ALFA SEM P

 

Hot carcass wt, kg

Dressing %'

Rib eye area, cm2

Leg scoreb

Back fat, cm

Yield grade

Kidney fat, 9

Quality Gradec

25.25 .54 24.97 .66 .03
50.01 .70 49.35 .86 .04
15.08 .40 15.72 .49 .21
12.3 .1 12.4 .1 .71
.56 .05 .47 .06 .09
2.59 .17 2.58 .21 .05
283 28 265 34 .23
18.25 .07 18.04 .08 .72

 

' Dressing percent calculated with kidney and pelvic fat removed from the

carcass.
b 10 = choice' = ; 11 = choice° ; 12 = Choice”.
° 17 = Choice' = ; 18 = choice° ; 19 = Choice“.

DISCUSSION

Experiment I - Individually-fed lamb feeding study.

Increasing lean tissue and decreasing fat associated with retail product is
extremely important in today’s fat conscious society. 8 - agonists and growth
hormone have been used extensively in research to maximize lean production
while simultaneously reducing fat; however, these agents have yet to approved
by the FDA for on-farm use. TO meet market demands for lean, less-fat meat
products, producers have been selecting for larger framed later maturing animals
for the past 30 years. This method of selection has increased lean to fat ratios
from about 1.0 to approaching 2.0 (Bergen and Merkel, 1991). Producers and
researchers alike have experimented with feeding diets that limit the amount Of
energy an animal receives in an effort to decrease fat production. An Objective
Of the present study was to determine if energy density has an effect on
performance and carcass characteristics when lambs were slaughtered at a
constant weight endpoint.

In the present study, all lambs were of the same breed cross and sex, plus
they were raised and managed at the same location and under the same
conditions throughout the trial. Thus, the trial was designed to have dietary

treatment as the only varrible In the experiment. Differences in the present study

74

75

reflect solely differences in energy density of the diet. Although diets were
formulated to have different ME values (ME mcallkg; CONC 2.79, ALFA 2.17)
lambs nearly consumed the same daily ME since ALFA-fed lambs increased their
DM intake. Results agree with similar studies by Glimp et al. (1989) and Crouse
et al. (1978) who showed that altering energy density of the diet did not reduce
energy intake because lambs consuming the lower energy density diet
compensated by increasing feed intake. Because ME intakes were similar it
would be anticipated that ADG would be the same; however the net energy (NE)
values of the diets differed. The ALFA diet had lower net energy for maintenance
(NEm) and lower net energy for gain (NEg) values. Thus the efficiency of
utilization of ME was greater for CONC-fed lambs.

Lambs in this trial were started on feed at the same weight and age and
slaughtered at a similar weight endpoint. Thus, no differences were found in total
gain or final weight of lambs; however, days on feed and ADG were affected by
dietary treatment. Lambs consuming the ALFA diet had lower ADG than the
CONC fed lambs, which is consistent with data reported by Crouse et al. (1978).
Lambs consuming the lower energy density diet experienced decreased (P<.05)
daily gain and thus needed extra (P<.05) days to reach the targeted weight
endpoint. Similar results were found by Burton and Reid (1969) comparing low
versus high energy diets. The authors reported lambs consuming a lower energy
diet experienced reduced gains and took a greater amount Of time on feed to
reach the targeted weight endpoint. The results in the present study are also in

agreement with those reported by Crouse et al. (1989) and Hart et al. (1989) with

76

sheep. Jesse et al. ( 1976) and Guenther et al. (1965) reported slower gains and
increased days on feed when feeding diets varying in energy density to steers.

Lambs were slaughtered at the same weight endpoint. Hot carcass weights,
however, followed a numerical trend to be heavier (P<.10) for CONC-fed lambs;
thus, Chilled carcass weights were also heavier (P<.05) for CONC-fed lambs than
for ALFA-fed lambs. When dressing percentage was calculated with kidney and
pelvic fat in the carcasses (Boggs and Merkel, 1993), CONC-fed lambs followed
a numerical trend to have higher (P<.10) dressing percentages. Murphy et al.
(1994) reported lambs consuming a 100% forage diet had lower dressing
percentages than lambs comsuming a concentrate diet. When removing kidney
and pelvic fat from the carcass, as practiced by the industry (USDA, 1992),
CONC-fed lambs had higher (P<.05) dressing percentages. The difference in
dressing percentage between treatments can be attributed to the effect of diet on
visceral organ mass. Although dressing percentage of CONC-fed lambs is
statistically different, the numerical difference is 1.5% different between
treatments. Because lambs on both treatments had the same starting and final
weights and were handled the same, dressing percentages were consistantly
1.5% different from each other. Thus, when tested statistically, a small difference
becomes significantly different.

Increasing dietary bulk in the diet has been shown to increase the weight of
visceral components (Murray and Slezacek, 1980; Koong et al., 1983; Ferrell and
Koong, 1985). In the present study, ALFA-fed lambs consuming greater amounts

of feed both on a daily basis and for the duration of the trial had heavier (P<.05)

77

empty GIT weights. Rompala et al., (1988) and Ferrell and Koong (1985) found
similar results when comparing lambs fed a low energy diet versus a high energy
diet.

Alfalfa-fed lambs had heavier (P<.01) empty omasum weights, whereas the
rumino-reticulum and abomasum were similar between treatments. In contrast to
the data reported in the present study, Rompala et al., (1988) reported an
increase in all stomach components Of the lamb. However, lambs were fed for
a longer period Of time in the study conducted by Rompala (1988). ALFA-fed
lambs consuming a higher level of bulk feed had heavier (P<.05) intestinal
weights. These results are consistent with observations by Ferrell et al. (1986)
and Jacobs and Lupton (1984), who found that increasing dietary bulk caused
hypertrophy Of the large intestine. Small intestine weights were affected by
treatment in a manner similar to large intestine. Alfalfa-fed lambs had heavier
(P<.05) small intestine weights. This is in agreement with studies by Jacobs
(1983), Jacobs and White (1983), and Johnson et al. (1985), who reported that
increasing dietary bulk increased the weight of the small intestine due to an
increase in cell proliferation. However, results in the present study are in contrast
with those of Goodland and Wright (1983) who reported that an increase in
dietary bulk decreased the weight of the small intestine. Rompala et al. (1988)
also found that when feeding diets that differed in energy density, the small
intestine was unaffected. Webster et al., (1994), restricting dietary energy to
growing lambs, by restricting feed intake, found no increase in weight Of the small

intestine. The data reported in the present study show that small intestine

78

weights increased 13% when raising the level of roughage from 25% to 100%
while simultaneously maintaining the level of ME intake and more than doubling
the NDF content Of the diet. In a similar study, Johnson et al. (1985) reported
that by increasing the level of roughage in the diet from 10% to 80%, while ME
intake remained relatively constant and NDF more than doubled, the weight of the
small intestine increased (P<.05) by 17%.

Dietary treatment did not affect heart or lung weights which is contrary to
results reported by Rompala et al., (1988), who noted that a 10% increase in
dietary bulk to the diet increased (P<.05) weights of these organs. However, the
results in this study were similar to those found by Aziz et al. (1993), who
concluded that severe energy restriction may reduce heart weight during periods
Of weight loss but that dietary intake of similar energy levels should have no effect
on heart or lung weights.

Liver weights for ALFA-fed lambs were heavier (P<.05) than for CONC-fed
lambs. Contrary to the findings reported here, dietary bulk did not increase liver
weights in studies conducted by Ferrell and Koong (1985), Rompala et al.,
(1988), Drouillard et al. (1991), Aziz et al. (1993) and Webster et al., (1994) when
feeding diets of lower energy content. Webster (1994) noted a 40% decrease in
liver mass of energy-restricted lambs, but after 2 d of realimentation, liver mass
was similar to those on unrestricted energy. Differences in results between
previous investigations and results presented here are likely due to the quality
and quantity Of feed the animals were Offered or the method that livers were

removed from the carcass.

79

No differences were found between dietary treatments for fat associated with
the GIT. Values reported here are higher than those reported by Aziz et al.
(1993). In the study reported here, lambs were slaughtered 20 kg heavier than
those slaughtered in the study conducted by Aziz et al. (1993). Thus, weight of
fat in the GIT would be expected to be higher. NO differences were found
between treatments in either study for fat associated with the ruminO-reticulum,
omasum, abomasum and small intestine. However, Aziz et al. (1993) found
greater amounts Of fat associated with the large intestine Of lambs experiencing
live weight loss than those undergoing live weight gain.

In the present study dietary, treatment did not affect carcass cutability (P<.05).
Thus, data reported here are in agreement with studies by Field et al. (1963),
Burton and Reid (1969), Winter at al. (1976), and Therize (1981), who reported
that age or nutritional treatment had no effect on carcass composition. The
authors also reported that carcass weight had the greatest influence on carcass
composition. In contrast to findings reported here, Murphy et al. (1994) reported
that finishing lambs on a 100% forage diet versus a concentrate diet can result
in decreased fat production when lambs were slaughtered at similar weights.

Backfat thickness between the 11th and 12th ribs was unaffected by dietary
treatment in the present study which was similar to results obtained by Field et
al. (1963) and Crouse et al. (1978). Results reported here are in contrast to those
of Osborne et al. (1961), Ray and Mandigo (1966) and Murphy et al., (1994) who
concluded that a reduction in dietary energy intake would ultimately lead to leaner

carcasses with less backfat when slaughtered at a similar weight endpoint.

80

Murphy et al. (1994) reported that forage-fed lambs would result in a 10%
reduction of fat on a carcass weight basis. However, carcass weights for forage
fed lambs decreased 10% between treatments. If lambs fed by Murphy et al.
(1994) had similar carcass weights there might have been a reduction in carcass
fat. In the present study, because backfat is the sole indicator Of lamb yield grade
(USDA, 1992), yield grade was proportional to backfat and unaffected by
treatment. However, Crouse et al. (1978) reported that higher yield grades were
influenced by a higher (P<.01) degree Of kidney and pelvic fat in lambs fed the
higher-energy density diet. Ray and Mandigo (1969) reported that lambs
consuming a diet higher in energy density had greater amounts of external fat,
while kidney and pelvic fat was unaffected. Crouse et al. ( 1978) reported results
for kidney and pelvic fat that are in contrast to those reported here. In the
present study, dietary treatment did not affect the amount Of kidney and pelvic fat
of lambs expressed either as an absolute weight or as a percentage Of carcass
weight, which is consistent with Ray and Mandigo (1969).

Leg conformation scores and ribeye area were unaffected by dietary treatment
which is consistent with results of Crouse et al. (1978).

Indicators of maturity and quality grade were unaffected by dietary treatment.
Maturity measurements of rib and lean color were similar between treatments.
In contrast, Crouse et al. (1978) reported that indicators of maturity were affected
by energy intake over time or at a constant final weight endpoint. Increased
maturity scores were primarily associated with increased feeding time required for

lambs fed a lower-energy density diet to reach slaughter weight. The increased

81

feeding time noted by Crouse et al. (1978) and Murphy et al. (1994) for lower-
energy density diets was greater than the extra days required by ALFA-fed lambs
in the present study. Scores for flank streaking, conformation, and quality grade
were in agreement with those reported by Crouse et al. (1978) and were
unaffected by dietary treatment.

The principle that carcass weight is directly related to composition Of the
carcass has been established (Bergen and Merkel, 1991). As weight increases
past maturity, fat becomes a greater proportion of carcass weight while
percentage of lean decreases. When animals are slaughtered at the same weight
endpoint carcass composition should not be affected by diet. It has been well
documented by Burton and Reid (1969), Winter (1976), MCC. Graham (1982) and
Orskov (1983) that the greatest influence on carcass composition is weight.
Murphy et al. (1994), Lambuth et al. (1970), and Kemp et al. (1976) concluded
that percentage of carcass fat is directly related to carcass weight. Thus it can
be concluded that carcass composition is directly related to absolute carcass
weight. In the present study, lambs were slaughtered at the same weight
endpoint; thus, no differences in total carcass composition were found between
dietary treatments when expressing fat, protein, water, and bone on a percentage
of the total carcass on a wet basis. Similar results were found by Burton and
Reid (1969) and more recently MCC. Grahm (1982) and Orskov (1983) when
using dietary treatments varying in energy density. In a more recent study,
Murphy et al. (1994) concluded that as dietary energy increased percentage Of

carcass fat increased in lambs consuming a higher-energy density diet. Even

82

though Murphy et al. (1994) reported similar slaughter weight endpoints, chilled
carcass weights differed between treatments by 10%. Chilled carcass weights
favored the lambs consuming the higher concentrate diet. Thus, if carcass
weights had been similar, differences in carcass composition between dietary
treatments may not have been shown (Burton and Reid, 1969; Winter, 1976;
MCC.Graham 1982; and Orskov, 1983).

The density of dietary energy did affect daily protein and fat accretion rates.
Concentrate-fed lambs deposited greater (P<.01) amounts of protein and water
as well as greater (P<.05) amounts of fat and bone. The data presented, are in
contrast to that by Murphy et al. (1994) who reported that lambs grazing alfalfa
versus a 100% concentrate ration had similar daily rates of lean tissue deposition
even though, daily fat accretion rates were greater for lambs consuming the 100%
concentrate diet. Daily accretion rates were not reported in other previously
mentioned studies. However, greater weight gains for lambs consuming the
higher-energy density diets were found by Burton and Reid (1969), MCC. Gram
(1982) and Orskov (1983). In the present study the amount Of fat deposited per
unit Of protein was unaffected by dietary treatment. Thus, fat-to-protein ratios
were similar between dietary treatments, which is in agreement with results
reported by MCC. Gram (1982).

When analyzing the nine cuts used to determine composition Of the carcass,
differences in weight of the cut were found for the shoulder and leg. NO
differences were found between cuts for analysis of tissue fat or protein. Thus,

there were no differences In the composition Of cuts, when composition was

83

expressed as a percentage Of cut weight. Heavier (P<.01) cut and boneless
tissue weights were found for the shoulder, along with the leg cut having heavier
cut (P<.01) and boneless tissue (P<.05) weights. Murphy et al. (1994) reported
heavier primal weights for the leg, shoulder, rack, and loin. The authors also
stated that lambs consuming the 100% concentrate diet had greater percentages
of fat than those grazing alfalfa (Murphy et al. 1994). Similar results were found
for weight and composition Of cuts for the rack, loin, breast, flank, shank, neck,

and kidney fat.

Economic analysis Of Individual fed lambs

Many producers believe that by feeding a 100% forage diet, they can produce
a leaner, more marketable product. Producers also believe that by feeding a
100% forage diet, which costs less per unit of feed than that Of a traditional high
concentrate ration, that they can reduce feed costs per head. Breakeven lamb
prices are presented in Table 26 for each diet. Diets were priced based on
current 1995 spring ingredient prices in the Mid-Michigan area. Lambs consuming
the CONC diet, which had a higher price per unit, consumed less feed and thus
had a lower feed cost on a per head basis than ALFA-fed lambs ($15.17 vs
$17.73, respectively). Lambs consuming the CONC diet were on feed 10 fewer
days and thus had a lower yardage cost than ALFA-fed lambs. Fixed costs were
the same between treatment and included the following: salt and mineral, death
loss, vaccine, shearing, commission, and interest (13%). Feeder lamb prices

were calculated by pricing a 75 lb lamb at $ 75.

84

Based on the current analysis, lambs consuming the CONC diet proved
beneficial in feed efficiency and ADG. Thus the CONC diet reduced the
breakeven price by $2.80 per head versus ALFA-fed lambs.

Lambs consuming the CONC diet converted feed more efficiently with higher
average daily gains offered more potential for profit than 100% forage fed lambs.
Although monitoring metabolic disorders was not part Of this study, CONC-fed
lambs may be more susceptible to metabolic disorders than ALFA-fed lambs. In
feedlot situations the opportunity to reduce bunk management and feedlot
disorders by feeding a 100% alfalfa pelleted diet may prove beneficial to

producers, and thus outweigh the increased cost of feed per head.

85

Table 26. Effect of dietary treatment on breakeven price if lambs

Dietary treatment

 

 

Item CONC ALFA
Feed consumed 189.6 lbs 272.8 lbs
Feed cost/ton 161.00 130.00
Total feed costs/hd 1 5.17 17.73
Days on feed 53 63
Yardage $.025/hd/d 1.33 1.57
Fixed Costs 7.09 7.09
Production Costs 23.59 26.39
75 lb lamb @ $75/cwt 52.50 52.50
Total Costs 76.09 78.89
Wool sales -2.00 -2.00
Breakeven price 4.09 6.89
Current Market

Price $82/cwt $92.40 $92.40
Profit/head $24.31 $21 .51

 

86

Experiment ll - Pen-fed lamb feeding study.

Not all of the results presented in Experiment I are in agreement with results
found in Experiment II. This difference may be caused by experimental design.
The 48 ewe and wether lambs in Experiment II were lambs that were left over
after 30 wether lambs and 15 replacement ewe lambs were selected from the
group. Thus younger, slower growing lambs that weighed less were used in the
trial explaining the increase in days on feed. Lambs were grouped four per pen,
and slaughtered when the pen averaged approximatly 52 kg. Lambs were
slaughtered on two dates when they were near the targeted weight endpoint to
facilitate slaughter at Wolverine Packing, Detroit, Michigan. Thus, there was
greater variation in slaughter weight Of the lambs with less variation in days on
feed. Because Of greater number Of lambs, less variation between treatments,
and consistent results within treatment, small numerical differences when tested
statistically become significant.

No differenes were found between treatments for average daily gain or days
on feed. Differences were observed in feed intake and were similar to results
reported in Experiment I. Alfalfa-fed lambs consumed more (P<.01) feed on a
daily basis and for the duration of the trial, both on an as-fed and DM basis than
CONC-fed lambs.

Similar relationships between treatments were Observed for dressing
percentage and carcass weight in Experiment II as in Experiment I. Higher
(P<.05) dressing percentages (1.3%) were observed in the CONC fed lambs.

Thus, CONC-fed lambs had 1.1% heavier (P<.05) hot carcass weights than

87

ALFA-fed lambs. Ribeye area and leg conformation score were not affected by
dietary treatment, which is similar to results reported in Experiment I and those
reported by Crouse et al. (1978).

Backfat thickness between the 11th and 12th ribs and yield grade were shown
to be significantly different for dietary treatments. Concentrate-fed lambs had .09
cm more backfat which tended to be greater (P<.09) than ALFA-fed lambs.
Comparing yield grades, the differences between dietary treatment means was
a tenth of a yeild grade; yet when tested statistically CONC-fed lambs were shown
to have higher (P<.05) yield grades. Although this difference is shown to be
significant, a tenth of a yeild grade equates to .09 cm of backfat which may be
attributed to rounding errors. Kidney fat was similar between treatments, but
when comparing this to results in Experiment I, the weight of kidney fat for both
treatments was much less. Lighter kidney fat weights may be due to less care

in removing all the fat from the pelvic cavity when lambs were slaughtered.

IMPLICATIONS

Results from the individually-fed lamb feeding study provide support that
moderate alterations in lamb growth does not affect overall composition of the
carcass when lambs are fed to the same weight endpoint.

Feedlot performance favored CONC-fed lambs, as expected. However,
acceptable levels Of performance were observed for ALFA-fed lambs. Feed
efficiency was improved in CONC-fed lambs because a greater amount of feed
was needed to attain acceptable gains in ALFA-fed lambs. Although ALFA-fed
lambs were consuming the diet with a lower cost per unit Of feed, their feed costs
were higher than CONC-fed lambs because of greater feed intake.

Visceral organ mass was affected when feeding a concentrate-based diet
versus an all-forage diet. Lambs consuming the forage diet experienced heavier
gasto-intestinal weights due to increased feed intake.

Diet did not affect total composition Of gain of lambs consuming either diet.
Daily accretion rates Of fat and protein were greater for lambs on the higher plane
Of nutrition. However, the ratio of fat deposited per unit of protein deposited was
similar. The similarity between treatments in fat and protein accretion ratios
supports the data showing that lambs are similar in composition when slaughtered

at a comparable weight endpoint.

88

89

Even though lambs consuming the lower-energy density diet exhibited lower
performance, adequate performance levels were attained while carcass
characteristics were unaffected. Thus, ALFA does have potential as a finishing
lamb diet. However, profit per head is reduced when feeding diets that do not
attain maximum daily gain or efficiency.

Accretion rates of fat and protein, combined with carcass composition data,
would suggest that feeding a 100% ALFA diet does not result in leaner carcasses

when lambs are slaughtered at a similar weight endpoint.

90

I ICHIGAN STATE UNIVERSITY

WWWMIALWWCA” ”WOWO‘itl!”
(WOMW
months-sou

W

TO: Bataan, Margaret . .
Animal Science
113 Anthony Hall of .

FROM: Richard 1. Aulerich, Chairperson /
All-University Committee on Animal Use Care

DATE: July 13, 1993

SUBJECT: APPROVAL OF APPLICATION TO use VERTEBRATE ANIMALS IN RESEARCH

Thisistonotifyyoudiatyourreceritapplieationtousevertebrateanimalsinruearchorteadringhasbeen
approved by the All-University Committee on Animal Use and Care. This approval is for a oneyear period,
beginning on the date of approval by the committee. ‘For external funding agencies. if the Office of the Vice
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willbeextended foroneyear followingthehrndingdate.‘
Myourprojedatmdbeymdmeyw,ywshwwreeubnutymrmqueumdnwmnunee. Fcryour
convenience, the new Yearly Renewal Form is designed so that resubmissions may be accomplished by merely
idattifyingtheearlierproposal andassuringthattheproposaiisbeingresubmittcdwithrevisions.
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to University policy, no significant changes may be made to your animal-use plan without prior approval from
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or by sending a letter to the AUCAUC. C103 Clinical Carter.

Title: LAMB PERFORMANCE AND CARCASS COMPOSITION ON LAMBS FINISHED ON
FELLETED DIETS OF FORAGE (ALFALFA) OR CONCENTRATE

AUP I: 7193-2364)! 0RD I: NIA
Funded By: DEPARTMENT
Approved: 07/08/93 Expires: 07/0804
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cc: Dr. Maynard G. Hogberg. Chairperson

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LIST OF REFERENCES

Allen, OM. 1966. The relationship Of some linear and physical measurements
to beef carcass composition. Ph. D. Thesis. Michigan State Univ. East Lansing.

American Sheep Producers Council. 1988. Lean lamb, a consumer choice, a
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