EFFECT OF DEGREE OF JIUSCLING OF FEEDER CATTLE LTON
SUBSEQUENT FEEDLOT PERFORMA^ICE AND
CARCASS CHARACTERISTICS
by
MELINDA ELAINE WEATHERBEE, B.S.
A THESIS
IN
ANIMAL NUTRITION
Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of
MASTER OF SCIENCE
Approved
Accepted
December, 1981 •'/
f 1
•' < * ,
•' -0 '/•"
ACKNOWLEDGEMENTS
I want to thank Dr. R. A. Long for his assistance with this thesis and my graduate studies. I appreciate Dr. C. B. Ramsey for his help in preparing this thesis. Committee members. Dr. C. R.
Richardson and Dr. F. C. Bryant, are appreciated for the guidance they have given. The help of the Texas Tech University Meats Lab crew in data collection is appreciated. I want to thank the Armour packing plant in Hereford, Texas, for the cooperation and services of its personnel. I appreciate the support and love my parents,
Orville and Frances Weatherbee, gave me during my graduate studies.
The friendship and concern of my fellow students is gratefully acknowledged.
11 TABLE OF CONTENTS
ACKNOWLEDGEMENTS ii
LIST OF TABLES iv
CHAPTER
I. INTRODUCTION 1
II. LITERATURE REVIEW 3
Visual Appraisal of Slaughter Steers 3 Measurements as Indicators of Carcass Composition 5 Feedlot Performance 11 III. EFFECT OF DEGREE OF MUSCLING OF FEEDER CATTLE UPON SUBSEQUENT FEEDLOT PERFORMANCE AND CARCASS CHARACTERISTICS 19
Summary 19 Introduction 20 Experimental Procedure 21 Results and Discussion 25 Initial Frame Size and Fat Thickness 25 Feedlot Performance 25 Carcass Characteristics 29 Relationship of Group With Feedlot Performance and Carcass Characteristics 31 Conclusions 34
LITERATURE CITED 35
111 LIST OF TABLES
Table Page
i. Percentage composition of diets 23
2. Least squares means (±SE) of feeder cattle measurements and fat thickness by muscle groups 26 3. Least squares means (±SE) of feeder cattle measurements and fat thickness by trimness groups 26
4. Least squares means (±SE) for feedlot performance by muscle groups 27
5. Least squares means (±SE) for feedlot performance traits by trimness groups 27
6. Least squares means (±SE) for carcass characteristics by muscle groups 30
7. Least squares means (±SE) for carcass characteristics by trimness groups 32
8. Simple correlation coefficients of feedlot performance and carcass characteristics with muscle and trimness groups ... 33
IV CHAPTER I
INTRODUCTION
Traditionally, feeder cattle have been evaluated by age, breed
and weight with some consideration for grades such as Prime, Choice
and Good, which were offered as a prediction of the quality grade
the feeder steer's carcass would produce at time of slaughter.
Even more unsophisticated grading systems were developed by the
feedlot industry for local use, an example of which would be the
"Okie" 1, 2 or 3 grades which meant different things to different
people. In 1979, the U.S.D.A. revised the feeder grades and based
them on thriftiness, frame size and thickness where variations in
"thickness" were said to reflect differences in ribeye area (REA)
or degree of muscling.
Thriftiness, as a description of animals in good health, is
universally understood and accepted as a desirable qualification
of feeder cattle. Frame size is generally accepted as affecting
the length of the feeding period necessary to reach a certain quality
grade with length of the necessary feeding period increasing as frame
size increases. However, differences in muscling are not as easily
recognized since "thickness" may be confounded with fatness. Further,
there is little data available as to the association of degree of muscling in feeder cattle with subsequent feedlot performance and carcass characteristics at time of slaughter. Therefore, the ob jectives of this study were to examine the effects of differences in muscling of feeder cattle upon: 1. Rate and efficiency of gain during the feeding period,
2. Characteristics of the carcass produced. CHAPTER II
LITERATURE REVIEW
Visual Appraisal of Slaughter Steers
Cattle buyers, packers, breeders and live animal judges rely on visual appraisal to evaluate the worth of an animal for breeding or marketing. The slaughter steer is evaluated for its ability to yield a desirable carcass. Koch (1978) determined that selec tion of cattle by muscling score was correlated with an increase in REA. His results indicated that selection for weaning or year ling weight would lead to increased carcass weight at a given age and a higher proportion of edible meat.
Cundiff et_ al^. (1967) visually scored 40 Angus steers for con formation, muscling and slaughter grade. They found live weight, rather than visual score, to be the best single indicator of weight of roast and steak meat. However, weight of cuts is not a measure of composition or cutability.
Live and carcass shapes of cattle and pigs were studied by
Kauffman £t al. (1973) to determine the influence of two distinct shapes (muscular and nonmuscular) on gross composition. Subjective evaluation favored nonmuscular animals, i.e., nonmuscular animals contained more fat than was suggested by visual appraisal and mus cular animals were leaner than expected. Also, muscle to bone ratios were not constant, ranging from 3.8 for the muscular cattle to 3.0 for the nonmuscular cattle. Similar differences (P<.01) were found in muscle to bone ratios for pork carcasses. However, degree of fatness was more important in determining carcass composi tion than was carcass shape. Muscular animals had higher dressing percentages; however. Callow (1944) attributed differences in dress ing percentage to stage of fatness of the animal. These results were based on data from 14 steers from five breeds with live weights from 295 to 636 kg and with differences in ages from 1 to 4 years.
Exotic breeds, which typically are heavily muscled, were not included in this study.
Schlegel (1979) used the scoring system of Long (1971) and found frame size useful in sorting cattle to determine the time on feed necessary to reach the Choice grade or the optimum endpoint for slaughter.
The relationships of visual appraisal of bone size and actual forecannon circumference to performance and carcass composition were evaluated by Dikeman e^ al. (1976) with 484 mostly crossbred steers. The steers were slaughtered after being on feed for 217,
242 or 284 days. Calves with the heaviest birth weights had the largest cannon bones at weaning and at slaughter. Results suggested that large bone size was associated with late maturing cattle. The steers with large bone size had trim carcasses, high carcass bone percentages and low quality grades (QG), indicating that the cattle were not fed to the same endpoint.
Good e^ al. (1961) evaluated 674 show steers over a 3-year period and found that steers scored as heavily muscled tended to dress higher and have larger REA than steers scores as lightly muscled. The correlation coefficients for muscling score and REA were signigicant, but were not large enough to be of value in pre diction. A significant negative correlation was found between REA and fat cover at the 12th rib, indicating that heavily muscled steers tended to have less fat.
Frame size, condition and muscling were subjectively scored and wither height and length of body were measured by Butts et^ al.
(1980b) on feeder calves before being placed on test. The steers were fed one of two levels of energy and individually slaughtered as they reached an estimated 12 mm of subcutaneous fat over the
12th rib. Initial scores for frame, wither height and length of body were highly correlated with each other but were negatively correlated with fat (P<.001). A subjective score for muscle ex pression was negatively correlated with frame, height and length
(P<.05) and positively correlated with fat. Calves with higher initial scores for frame and lower scores for fat produced heavier carcasses. However, 23 steers failed to reach the estimated 12 mm of fat thickness (FT) before slaughter, indicating that all of the cattle did not have the opportunity to reach the same stage of phy siological maturity.
Measurements as Indicators of Carcass Composition
Muscle. The efficient production of muscle should be a goal of the beef cattle industry. Several studies have been conducted to determine the value of a measure of muscle as an indicator of carcass composition. Circumference of round had a significant posi tive correlation with fat cover at the 12th rib (Good £it al. , 1961) Davis and Long (1962) used a Branson Sonoray to ultrasonically esti mate the REA and FT between the 12th and 13th ribs of slaughter steers. Estimates were highly correlated with actual REA (r = .87) and FT (r = .90).
Orme et^ al. (1960) determined that the weights of six muscles and two groups of muscles were associated with 14 to 92% of the variation in the weight of the total separable carcass lean. As would be expected, the separable lean of a particular beef cut was more descriptive of carcass leanness or muscling than was REA.
Cole e^ al^. (1960) found that REA was associated with only 18% of the variation in separable carcass lean. They demonstrated the validity of using the weight of certain entire muscles to estimate the degree of muscling in a particular beef carcass. Callow (1961) slaughtered 24 steers of three breeds when estimated to dress 57%.
The percentage of fatty tissue was inversely proportional to per centage of muscular tissue. Muscle to bone ratios were not signifi cantly different in the Friesian, Shorthorn and Hereford steers studied.
Hedrick et_ al. (1965) demonstrated that bilateral measurements of fat and muscle were not significantly different, establishing the validity of using carcass data from one side of a carcass.
Muscle area was more highly correlated with weight than with per centage of retail cuts.
Berg and Butterfield (1966) dissected 62 animals from six breed groups. The groups differed significantly in muscle to bone ratio when adjusted to a common level of total muscle, fat, muscle plus bone and carcass weight. In contrast, Koch et_ al. (1979) found only slight differences in muscle to bone ratios among groups of purebred and crossbred cattle (N = 775). Steer carcasses were com pared after adjustment to equal age, weight, FT, fat trim percentage and marbling score endpoints. A small variation in retail product was observed at a constant calculated fat trim percentage. There fore, the researchers concluded that breed groups did not differ significantly in muscle to bone ratio. However, no dissection data for muscle and bone were presented to support this statement. O'Mary et al. (1979) found small differences in muscle to bone ratios be tween Angus and Charolais-Angus steers.
Kauffman et^ ^. (1976) compared 31 steers with varying degrees of muscling. More muscular steers yielded heavier (P<.01) carcasses than fatter steers when holding live empty body weight (LEBW) and fatness constant. Koch (1978) found that selection for muscling favorably changed body composition.
Skeleton. Breeders and buyers use visual estimates of frame size and circumference of bone in the evaluation of cattle. Re searchers have measured cattle in an effort to determine if measure ments are repeatable and to determine if amount of bone has an ef fect on muscling and cutability. Tallis et^ ^. (1959) found that height at the withers, height at the hooks, heart girth and navel circumference had high repeatabilities. Length of body, depth of chest and width of hooks also had high repeatabilities. Orme £t_ al.
(1959) computed repeatability estimates of .96 for height measure ments (at the withers and rump) and .94 to .99 for measures of circumference (fore, flank and middle). Measurements of width of round, rump and shoulder had repeatability estimates ranging from
.84 to .88.
Yao £t_ al. (1953) found that height at the withers was highly correlated with all other height measurements and that length of body was significantly correlated with length of coupling and length of rump. Kohli et^ a]^. (1951) measured Milking Shorthorn steers.
Length of body tended to be positively associated with height mea surements (height at withers and height to floor of chest). Wythe e_t_ al. (1958, 1961) confirmed that bone in cattle develops propor tionally in both length and weight.
Ramsey _et^ al. (1976) classified Hereford bulls, steers and heifers as medium or large type. Differences (P<.05) between sexes were found. Bulls were longer than steers or heifers. \\Tien skele tal measurements were expressed as a percentage of some other skel etal measurement to obtain body proportions, differences between sexes and types were eliminated. Similar results were found regard ing proportionality of cattle by Orme et_ ^. (1959) and Butts ejt al.
(1980a)
Height at the withers of 410-kg steers, was negatively corre lated (P<.05) with slaughter grade, carcass grade and dressing per cent (Cook ^ _aJ^. , 1951). These steers were not slaughtered at the same physiological endpoint.
Weight of bone was positively related to pounds of lean (Wood ward e^ ^. , 1959) . Wythe et_ al. (1961) demonstrated a strong posi tive relationship between bone thickness (as expressed by weight to length ratio) and trimmed boneless cuts. Wilson e^ al. (1977)
found that metacarpal and metatarsal density and dimensions were
positively correlated with the production of edible portion per
day. Orts (1959) examined cannon bone weight and area, weight to
length ratio and specific gravity (SG). These factors had a high
relationship with wholesale cuts weight and REA. Skelley et^ al.
(1972) found significant positive correlations between metacarpus
circumference and wholesale cuts of the carcass. Also, hind and
foreshank circumference was significantly and negatively correlated
with percent kidney fat of the carcass.
Body measurements taken before slaughter of 50 beef steers
were correlated with weights of wholesale cuts by I-Jhite and Green
(1952). The correlation coefficients for the various cuts were:
rib, .97; rough loin, .98; trimmed loin, .97; and round, .93. Green
(1954) found that the single measure most closely associated with
the weights of the round and trimmed loin was live weight. However,
these correlations did not indicate the lean or fat composition of
the cuts. Carcass weight was highly associated with separable lean
(Cole et^ al., 1962) and to boneless steak and roast meat (Abraham
ejt al. , 1968). However, Brungardt and Bray (1963) suggested total
carcass weight was a poor indicator of percent edible portion or
muscle.
Fat. Lush (1928) observed that, in general, steers increased more in width during fattening than they did in length or depth of
body and least of all in height. "Fat is the most variable tissue
in the body...," stated Berg and Butterfield (1976). Kauffman 10 ejt al. (1973) compared muscular and nonmuscular pigs. The four lean cut percentages and the ham and loin percentages when compared with percent total extractable fat constant were not different. There fore, fat was responsible for more variation in lean cut yields than degree of muscularity. Butts e^ al. (1980b) observed that differ ent sized cattle had similar carcass characteristics other than weight when they were slaughtered at the same degree of finish.
However, the same FT on steers of different weights may not yield carcasses with the same composition because the same FT on a smaller steer could make up a larger percentage of his body weight.
Kidwell et^ al. (1959) found that carcasses with higher QG yielded more fat, but less bone and muscle. Carcass grade was found by Ramsey et^ al. (1962) to be positively related to percentage of separable fat (r = .79) when breed effects were ignored in a study involving 133 steers of varying breeds and crosses. Also, neither carcass grade nor YG was superior to a single FT measurement or an average of three FT measurements over the ribeye as an estimator of percent separable lean and fat. Brackelsberg and Williams (1962) in a study with 51 head of cattle found the most valuable measure ment for fat was a probe over the ribeye at the 12th rib. Simple correlations indicated that this live measurement of FT was as ac curate as the conventional 12th rib measurement of FT in the car cass for predicting total carcass fat trim. 11
Feedlot Performance
Washburn (1948) compared three conventional and three compact
Shorthorn steers. The conventional type steers were more efficient in feed utilization but required a longer feeding period to reach
the slaughter condition of the compact steers. Kidwell and McCor- mick (1956) evaluated the performance of Holstein and Hereford
steers. The steers of larger mature size gained more rapidly on
less feed than steers of smaller mature size. However, all of the
steers were not fed to the same endpoint. In one of the trials,
the Holstein steers averaged 15 months of age and the Herefords
averaged 20 months when placed on feed. Furthermore, carcasses
of the larger steers contained a higher proportion of bone and mus
cle and a lower proportion of fat. In 1959, Kidwell ejt _aJ^. found
no relation between feeder grade and subsequent rate of gain and
feed efficiency.
Rate of growth and feed efficiency of 290 purebred Hereford
and Angus calves were evaluated by Bogart et^ ^. (1963) . Growth
rate increased to a weight of 132 kg but was almost constant there
after. Feed efficiency decreased from weights of 227 to 364 kg
even though growth rate did not change during this period. More
rapidly growing calves converted the feed into body weight gains
more efficiently than less rapidly growing calves even though they
ate no more per unit of body weight.
Blaxter et_ al^. (1966) observed that younger animals retained
nitrogen more efficiently than older ones. When nitrogen and en
ergy metabolism were measured, protein energy accounted for 30.5% 12
of the total energy retained in 15-week-old calves and 24.8% in
calves 81 weeks of age. The experimental animals were not slaughtered
to determine the composition of their gain.
Bailey e^ aJ^. (1966) compared the feedlot performance and body
composition of bulls and steers. Bulls grew more rapidly (P<.05)
than steers during feedlot testing and appeared to have an advantage
in feed efficiency. Also, steer carcasses had more fat (P<.01),
less muscle (P<.01) and less bone (P<.05) than bulls. Hedrick et al.
(1969) made the same comparison between bulls, steers and heifers.
Bulls were superior to steers and heifers in live weight gain (P<.05)
and in feed conversion. Total weight and percent retail cuts of
the carcass were greater (P<.05) for bulls than for steers and hei
fers. Intermuscular fat increased with increased time on feed.
Bulls may have an advantage in feed efficiency due to the leaner
composition of their gain. Williams (1965) found bulls gained
faster and more efficiently in a feedlot situation than steers or heifers.
Fox et ^1_. (1972) demonstrated that steers restricted in feed
intake had carcasses lower in fat (P<.01) and higher in protein percentage (P<.05). Knox and Koger (1946) classified steers as
rangy, medium or compact prior to feeding for 168 days. Rangy steers weighed more and had higher dressing percentages than medium or compact steers when slaughtered. Amount of gain was positively correlated with initial weight. Seven regular and seven "comprest" steers were fed a growing ration for 112 days and a fattening ra tion for 173 days by Willey et^ al. (1951). The regular and "com- 13 prest" steers had about the same rate of gain for the growing phase and the first 60 days of the fattening phase. Then, the rate of gain for the "comprest" steers declined. Dressing percent was not different, but the groups of "comprest" steers had a greater num ber of steers in the Choice grade at slaughter. Stonaker et al.
(1952) studied "comprest," intermediate and large type steers.
The intermediate and large steers ate more, had higher average daily gains and reached low Choice weighing 20% more than the "com.- prest" steers when all steers were fed to an estimated 1.3 cm of fat over the ribs.
Cole et_ aJi^. (1963) , using steers from six breeds and one cross of British, Zebu and dairy breeding, found that Hereford steers gained slightly faster with a higher feed efficiency than
Angus steers. Holstein steers gained the fastest of all breeds on less feed, but graded lowest.
Zimmerman et_ al. (1966) fed 20 Hereford yearling steers and
20 Hereford steer calves to determine their rate of gain and feed efficiency. One-half of the yearlings and calves were fed until visually appraised to grade low Choice, and the remaining yearlings and calves continued on feed for at least 90 kg of additional gain.
With increased time on feed, daily gain decreased and more feed was required per unit of gain for both yearlings and calves.
Garrett (1971) conducted comparative slaughter experiments with Holsteins and Herefords. Herefords were 12 to 20% more effi cient than Holsteins in converting feed energy consumed above main tenance to energy storage as fat and protein. The gains of the 14 beef steers contained more fat and therefore more energy than com parable gains by dairy steers.
Smith £t^ al. (1976) collected data from 1,105 steers out of
Hereford and Angus cows by Hereford, Polled Hereford, Angus, South
Devon, Limousin, Charolais and Simmental bulls. One-third of the steers were selected at random in each sire breed by dam breed sub class to be slaughtered at one time. The average times on feed for the groups killed in the 3 years of the experiments were 184 days for the first one-third, 218 days for the second one-third and
251 days for the final one-third. Faster gaining breeds tended to be more efficient than slow gaining breeds. Rapid growth contributed to a more desirable feed efficiency when feed efficiency was measured over weight constant intervals because fewer days of maintenance were required. The more desirable feed efficiency of fast growing breed groups could be due to the leaner com.position of their gain and their resultant lower caloric density.
Dean et^ al. (1976) fed calves from Hereford, Hereford-Holstein and Holstein cows by Angus and Charolais bulls to low Choice. Hol stein progeny were taller, longer and older at slaughter. Progeny of Holstein and crossbred cows consumed more total feed, more feed daily and required more feed per unit of gain than Hereford progeny.
Shape as assessed before cattle were placed on feed was not a determinant of feed conversion when LEBW and fatness were held constant (Kauffman et al., 1977). However, data supported research suggesting that degree of fatness affects efficiency. More muscularly- shaped cattle at a given weight were more efficient converters of feed 15 to fat-free muscle because they were leaner and possibly not as mature as less muscular cattle.
Fecal starch. Fecal starch is an estimate of the amount of dietary starch that has escaped utilization in an animal's digestive tract. Maynard and Loosli (1975) reported that the newborn calf develops the ability to digest starch and has a coefficient of di gestibility of 90% at 4 weeks of age. Waldo (1973) examined the roles of starch in the diet. Starch was first subjected to micro bial fermentation in the rumen with its consequent production of cells and volatile fatty acids and, secondly, to enz3rme digestion in the small intestine, producing glucose.
Karr et a]^. (1966) fitted 360-kg Angus steers with cannulas in the rumen and either the abomasum or the posterior ileum to study sites of digestion. The steers were fed a ration of 2.5 kg of one of four diets with starch levels ranging from 19 to 63.5%. The percentage of starch apparently digested in the gastrointestinal tract ranged from 97.7 to 99. Karr e_t al. (1966) and Little et al.
(1966) concluded that postruminal digestion was inadequate for the optimal utilization of starch. Little et^ al. (1968) observed appar ent starch digestion percentages ranging from 82.1 to 95.9 in 370-kg steers. The steers were fed a basal ration of 4 kg of ground hay with a purified corn starch slurry given twice daily through an abomasal cannula at levels from 200 to 600 g. Significantly more starch reached the feces with 400 and 600 g infusions than with
200 g infusions. 16
Galyean e^ al. (1976) fed 429-kg Hereford steers rations con taining 78% processed corn (dry matter basis) that had been processed by one of four methods (dry rolled, steam flaked, high moisture harvested-ground prior to ensiling, or high moisture harvested-whole corn treated with propionic acid prior to storage). Total starch digestibilities ranged from 95.8 to 99.9%. Intestinal starch di gestibility was not greatly different among the four methods of processing grain in the ration, but the effect of higher dietary intake levels was not determined.
0rskov £t al. (1969) studied lambs that were weaned and placed on test at 5 weeks of age. Lambs were allowed either ad libitum consumption or a restricted intake of 70% of _ad libitum. In experi ment I, the diet was a concentrate containing 80% rolled barley,
4% molasses, 7% soybean meal, 5% fish meal, 2% minerals, 1% poly ethylene glycol, and 1% salt. In one treatment, rolled barley was replaced by ground barley, and in another treatment the concentrate contained 50% rolled barley, 28% maltose, 9% soybean meal, 5% fish meal, 2% minerals, 1% polyethylene glycol and 1% salt. A ration was also composed of 60% of the rolled barley concentrate and 40% dried grass. In experiment II, flaked corn, ground corn or cracked corn was substituted for the rolled barley in the first diet men tioned. Lambs on the all concentrate rolled barley and maltose diet ad libitum had .7% starch in the feces on a dry matter basis.
The lowest percentage recorded was .4 for lambs receiving an ad libitum or restricted diet of 60% rolled barley and 40% dried grass or a concentrate diet of ground barley. In experiment II, the 17 flaked, ground or cracked corn in the concentrate raised the per centage of starch in the fecal dry matter to 1.1 to 2.0. However, mean values never exceeded 1% of dietary intake. Live weight gain was recorded in experiment I. Lambs with restricted intake had
lower gains. The highest daily gains were made by lambs receiving
the rolled barley and maltose concentrate at ad libitum levels.
The iambs consuming the ail concentrate rolled barley and the 60%
rolled barley plus 40% dried grass had gains of .19 and .22 kg/day,
respectively, with ad libitum intake levels.
Waldo (1973) reviewed previous research on starch digestion
in ruminants. Starch digestibility for all grains in the total
tract was 99 ± 1.2%. Feeding large particle sizes to cattle re
duced digestibility in some experiments.
Hinman and Johnson (1974) studied sorghum that had been dry
rolled, micronized, steam flaked or ground. Differences in total
starch digestion as a percentage of total starch intake ranged from
92.4 to 99.6 with micronized and steam flaked sorghum having the highest
digestibilities. The effect of micronizing or steam flaking sorghum
on efficiency of performance was not discussed.
Wheeler e_t al. (1975) fed dairy cows diets with differing
forage to concentrate ratios. At an intake near maintenance, di
gestibility of starch ranged from 96.2 to 96.8%. During lactation
(with intakes from 2.5 to 3.2 times maintenance), digestibility
of starch ranged from 84.7 to 88.1%. Wheeler _et_ al^. (1976) found
that the percentage of starch in the feces increased with an in
crease in the amount of concentrate in the diet of dairy cows. 18
In another trial of the same experiment, three groups of three steers each were fed an all-concentrate diet based on either rolled barley, whole kernel corn or cracked corn. These steers had fecal starch percentages ranging from 19 for a barley diet to 40 for a corn diet.
Decreased utilization of starch by ruminants fed a high energy diet m ight be due to reduced alpha-amylase activity at the lower intes
tinal pH resulting from high energy diets with ad libitum consump
tion. In the final segment of this experiment, ad libitum intake
of high energy diets decreased the pH throughout the gastrointestinal
tract and in the feces.
Wheeler and Noller (1977) studied Holstein steers and cross
bred ram lambs. Starch content of the feces was negatively corre
lated with fecal pH. CHAPTER III
EFFECT OF DEGREE OF MUSCLING OF FEEDER CATTLE UPON
SUBSEQUENT FEEDLOT PERFORMANCE AND
CARCASS CHARACTERISTICS
Summary
Thirty Charolais crossbred, weanling, feeder steers of the
same frame size were grouped for muscling and trimness. Skeletal
linear measurements were taken and fat thickness (FT) was determined
ultrasonically. During the feeding period, individual feed consump
tion and performance data were recorded and periodic fecal samples were collected for starch determinations. After 195 days on feed
the steers were slaughtered and carcass evaluation and data obtained.
No significant differences were found in initial FT or in skeletal measurements, except for a difference in rump length when the steers were grouped by trimness. Feed efficiency was not different when
the steers were grouped by trimness, but a difference in feed effi
ciency was observed when the steers were grouped according to musc
ling. The light-muscled steers were more efficient than the heavy- muscled steers. ADG was not different when grouped by muscle, but when grouped by trimness the medium and trim steers gained signifi
cantly more than the wasty steers. The fecal starch I percentage of the medium-muscled steers was significantly higher than for the
light- and heavy-muscled steers. The fecal starch III percentage was significantly lower for the trim steers in comparison to the wasty steers. Dressing percent, quality grade, specific gravity,
19 20
yield grade and FT were not different when the steers were grouped
by muscle or trimness. Heavy-muscled steers had significantly larger
ribeye areas (REA) and higher conformation scores. The medium and
trim steers had significantly larger REA than the wasty steers.
Conformation score was significantly different for the three trim
ness groups. Visual scoring for muscling and trimness of feeder
calves did not result in differences in feed efficiency that were
large enough to be of value in predicting feedlot performance.
Steers classified as trim and heavily muscled tended to produce
carcasses with higher cutability than steers which were wasty and
thinly muscled.
Introduction
Traditionally, feeder cattle have been evaluated by age,
breed and weight with some consideration for grades such as Prime,
Choice and Good, which were offered as a prediction of the quality
grade the feeder steer's carcass would produce at time of slaughter.
Even more unsophisticated grading systems were developed by the
feedlot industry for local use, an example of which would be the
"Okie" 1, 2 or 3 grades which meant different things to different people. In 1979, the U.S.D.A. revised the feeder grades and based
them on thriftiness, frame size and thickness where variations
in "thickness" were said to reflect differences in REA or degree of muscling. 21
Thriftiness, as a description of animals in good health, is universally understood and accepted as a desirable qualification of feeder cattle. Frame size is generally accepted as affecting
the length of the feeding period necessary to reach a certain qual
ity grade with length of the necessary feeding period increasing
as frame size increases. However, differences in muscling are not
as easily recognized since "thickness" may be confounded with fat
ness. Further, there is little data available as to the association
of degree of muscling in feeder cattle with subsequent feedlot per
formance and carcass characteristics at time of slaughter. There
fore, the objectives of this study were to examine the effects of
differences in muscling of feeder cattle upon:
1. Rate and efficiency of gain during the feeding period.
2. Characteristics of the carcass produced.
Experimental Procedure
Thirty crossbred, weanling, feeder steers from the same ranch,
weaned at the same time, sired by Charolais bulls and visually
selected to be of the same frame size, but with differences in
muscling, were utilized. The cattle were visually scored by the
method of Long (1971) for waste, degree of muscling and frame size.
This method uses a scale from 1 to 10 with 10 indicating a larger
frame size or greater degree of muscling or trimness. Higher scores
for muscling were given to steers with more bulging forearms, thicker
stifles in relation to width of hooks, and more muscle expression
during miovement. Steers with trim briskets and tight dewlaps, under- 22
lines, flanks and twists were assigned higher trimness scores.
Steers scored 3 or 4 for muscling or trimness were considered light-
muscled or wasty. Scores of 5 or 6 were considered medium in
muscling or trimness. Steers scored as 7 or 8 were considered
heavy-muscled or trim.
Skeletal measurements were taken to the nearest millimeter
on 2 consecutive days before the start of the test. A metal cali
per was used to measure height at the withers, height at the hips,
length of rump (from hooks to pins) and length of body (from point
of shoulder to the pins). A metal tape was used to measure the
length of the right metacarpus and metatarsus. The measurements
were taken from the lateral condyle of the proximal end to the
distal synarthrosis of each bone. Circumference of the metacarpus
and the metatarsus and the overlying tissues at the smallest point
was determined with a metal tape. FT was measured by a Model 12
Branson Sonoray instrument. On each of 3 consecutive days at about
1400 hr, each steer was weighed and the average used as the on-test weight.
During a 2-week period, the steers were gradually introduced
to the ration they would be consuming for the first 113 days on
test. This ration contained 1.56 mcal/kg NE , .92 mcal/kg NE^ and m g about 51.4% starch. For the remainder of the study the steers were
fed a concentrate ration containing 1.72 mcal/kg NE^, 1.09 mcal/kg
NE and about 63.7% starch. The composition of the diets is given g in table 1. Salt was available to the steers free choice. Two 23
TABLE 1. PERCENTAGE COMPOSITION OF DIETS
Internat'1 Diet''"' Ingredient ref. no. 1 2
Ground yellow corn 4-02-992 32.5 49.5
Rolled oats 4-03-307 15.0 15.0
Wheat bran 4-05-191 5.0 3.8
Pelleted alfalfa hay, 17% protein 1-00-122 5.0 3.8
Cane molasses 4-04-696 5.0 5.0
Soybean meal, solv-extd, 47% protein 5-04-604 7.5 5.7
Cottonseed meal, solv-extd, 41% protein 5-01-621 5.0 3.8
Cottonseed hulls 1-01-599 24.5 13.0
Ground limestone .5 .4 c Vitamin A
Total 100.0 100.0
Air dry basis.
^Diet 1 was fed for 113 days and diet 2 from 114 to 195 days for kill group 1 and to 202 days for kill group 2.
"2200 I.U./kg 24
Pinpointer^ 4000 electronically activated feeders were used to moni tor and record individual feed consumption. Every 28 days, beginning at about 1400 hr, the steers were weighed and ADG, feed consumption and feed efficiency were calculated.
Visual scores and linear measurements were repeated at the end of the test. The steers were slaughtered when estimated to grade 70% Choice. Fifteen steers were slaughtered after 195 days on feed and the remaining 15 were slaughtered 1 week later at the
Armour packing plant in Hereford, Texas. Carcass data were collected
after 48 hr of chilling. The left side was shipped to the Texas Tech
University Meats Laboratory where specific gravity was determined
by hydrostatic weighing. The sides were fabricated into boneless,
closely-trimmed (<1 cm) retail cuts and ground beef (about 20% fat) .
A fecal sample was taken from each steer on the 28th, 140th
and 168th day on feed, and starch was determined according to the
method of Shetty ejt a]^. (1974) , with the assistance of a technical
bulletin.^ This method involves the gelatinization of the starch,
leaving the starch susceptible to the action of gluco-amylase. Glu
cose was determined by the glucose oxidase method.
Simple correlation coefficients were calculated between muscle
or trimness groups (a score of 3 or 4 was coded as 1; 5 or 6 was
coded as 2; 7 or 8 was coded as 3), and skeletal measurements, feed-
lot performance and carcass traits. The data for feedlot perform-
^UIS Corporation; Cookeville, Tennessee.
^Flozyme-technical bulletin SM526034. Worthington Diagnostics, Freehold, NJ. 25 ance and carcass traits were analyzed by a complete random design analysis of variance, and Duncan's new multiple range test was used to determine significant differences between muscle and trimness groups (Steel and Torrie, 1960; Barr £t al., 1979). The predeter mined acceptable level of probability was 5% and is used throughout
this thesis.
Results and Discussion
Initial frame size and fat thickness. Least squares means and
standard errors for initial linear measurements of skeletal size and degree of fatness by muscle and trimness groups are in tables
2 and 3. No significant differences were found between group means
for any linear measurement except rump length (among the steers grouped by trimness). This measurement (from hooks to pins) includes fat
tissue overlaying the pin bones. However, the sonoray estimate of fat thickness was not different over the 12th rib. The similarity of these means and the small standard errors indicate that these steers were of the same frame size. The fat thickness as measured by sonoray ranged from .5 to 1.5 cm but neither muscle nor trimness groups differed. This result establishes that the cattle were uni form in condition.
Feedlot performance. Least squares means and standard errors for feedlot performance traits of the steers by muscle and trimness groups are in tables 4 and 5, respectively. Weights on test for the light-muscled steers were significantly lower than for the steers with medium- or heavy-muscling. Weight off test was lower for the light- 26
TABLE 2. LEAST SQUARES MEANS (±SE) OF FEEDER CATTLE MEASUREMENTS AND FAT THICKNESS BY MUSCLE GROUPS
Muscle groups Light' Medium Heavy Measurement (N=li) (N=7) (N=12)
Height at hips, cm 109.5 ± .6^ 111.3 ± .7 109.5 ± .5 Height at withers, cm 104.3 ± .6 105.3 ± .7 103.4 ± .5 Length of rump, cm 39.5 ± .3 39.8 ± .4 39.8 ± .3 Length of body, cm 119.1 ± .9 120.8 ±1.3 120.3 ± .9 Length of metacarpus, cm 15.6 ± .2 16.1 ± .2 15.6 ± .2 Length of metatarsus, cm 17.9 ± .2 18.0 ± .2 18.0 ± .2 Sonoray fat thickness, cm .6±.l .9±.l .7-.1
Means in each row are not different (P<.05).
TABLE 3. LEAST SQUARES MEANS (±SE) OF FEEDER CATTLE MEASUREMENTS AND FAT THICKNESS BY TRIMNESS GROUPS
Trimness groups Wasty Medium Trim Measurement (N=6) (N=16) (N=8) Height at hips, cm 109.4 ± .8 109.9 ± .5 110.6 ± .7 Height at withers, cm 104.3 ± .8 104.3 ± .5 110.6 ± .7 Length of rump, cm 39.6 ± .4^^ 40.0 ± .2^ 39.2 ± .3^ Length of body, cm 118.2 ±1.2 120.9 ± .7 119.3 ±1.0 Length of metacarpus, cm 15.6 ± .2 15.7 ± .1 16.0 ± .2 Length of metatarsus, cm 17.7 ± .2 18.0 ± .2 18.0 ± .2 Sonoray fat thickness, cm .7±.l .7-.1 .7-.1
^*^Means in the same row with different superscripts are different (P<.05). 27
TABLE 4. LEAST SQUARES MEANS (±SE) FOR FEEDLOT PERFORMANCE BY MUSCLE GROUPS
Muscle groups Trait Light Medium Heavy
Weight on test, kg 244.6± 3.9^ lll.lt 4.9^ 265.3± 3.7>' Weight off test, kg 461.6± 11.9^ 501.1± 15.0^ 491.4± 11.4^'= ADG, kg 1.1± .1 1.2± .1 1.2± .1 Average daily feed consumption, kg 8.8± .3^ 10.3± .4^ 10.2± .3" Feed/gain 8.1± .2^ 8.7± .3^^ 8.8± .2" Fecal starch I, %^ 6.5± 1.0^ 10.5± 1.2^ 4.0± .9^ Fecal starch II, % 5.6± 1.6 8.4± 2.0 3.4± 1.6 Fecal starch III, % 10.5± 1.5 8.6± 1.9 7.5± 1.3 a b * Means in the same row with different superscripts are different (P<.05). 'Fecal starch I, II and III were sampled on day 28, 140 and 168 of the feeding period, respectively.
TABLE 5. LEAST SQUARES MEAJIS (±SE) FOR FEEDLOT PERFORMANCE TRAITS BY TRIMNESS GROUPS
Trimness groups Trait Wasty Medium Trim
Weight on test, kg 243.0± 6.4^ 263.0± 4.0 264.6± 5.5 Weight off test, kg 434.7± 14.4^ 499.8± 8.8^ 410.5± 12,4^ ADG, kg 1.0± .06' 1.2± .03 1.2± .05' Average daily feed cons ump t ion, kg 8.3± .5' 9.9± .3 10.3± .4 Feed/gain 8.5± .3 8.3± .2 8.9± .3 Fecal starch I, % 6.7± 1.8 6.6± 1.0 6.1± 1.6 Fecal starch II, % 6.3± 2.2 4.5± 1.4 7.1± 2.1 ab Fecal starch III, % 12.5± 1.9' 8.5± 1.1 6.6± 1.6^
^' Means in the same row with different superscripts are different (P<.05). ^Fecal starch I, II and III were sampled on day 28, 140 and 168 of the feeding period, respectively. 28 muscled steers than for the medium-muscled steers. The wasty steers were different in weight on and off test, being lighter than the med ium or trim steers. The steers were of the same frame size, so in creases in weight could be attributed to increases in fat or muscle.
The trim steers were heavier than the wasty steers.
Feed consumption followed expected patterns with heavier steers consuming more pounds of feed per day than lighter steers. The heavy- and medium-muscled steers consumed significantly more feed than the light-muscled steers. The wasty steers, which were lighter in weight, consumed significantly less feed than the medium or trim steers.
ADG was not different for the steers when grouped according to muscle score. When grouped according to trimness score, the wasty steers had a significantly lower ADG than the trim or medium steers.
The light-muscled steers were significantly more efficient than the heavy-muscled steers in feed to gain ratio and the medium-muscled steers were not different from the heavy- or light-muscled steers.
These results are in conflict with those of Hembree (1980) in which no difference in feed to gain ratio was found when the steers were grouped according to muscle. Steers grouped by trimness were not different in feed to gain ratio.
Fecal starch percentages were examined by muscle and trimness groups. The fecal starch I percentage of the medium-muscled steers was significantly higher than the fecal starch I percentage of the light- and heavy-muscled steers. Nonsignificant differences were found for fecal starch II and III when grouped according to muscle. 29
When the steers were grouped according to trimness, no differences were found in fecal starch I and II percentages. The fecal starch
III percentage was significantly lower for the trim steers than for the wasty steers; however, the medium steers were not significantly different from the wasty or trim steers. The lower starch digesti bility by the wasty steers near the end of the feeding period is unexplainable in view of the lack of difference among trimness groups for ADG, feed to gain or measures of fatness.
Carcass characteristics. The least squares means and standard errors for carcass characteristics by muscle group are presented in table 6. Dressing percentage was not different for the three groups, agreeing with the findings of Hembree (1980). The medium-muscled steers had a significantly larger side weight than the light-muscled steers.
When grouped according to muscle, steers that were heavy-muscled had significantly larger REA, which is in agreement with Good e^ al.
(1961), Schlegel (1979) and Hembree (1980). Conformation scores were significantly higher for the heavy-muscled steers than for the light- muscled steers. Although not significantly different, every measure of cutability except fat thickness ranked the heavy-muscled steers as most desirable.
Percent bone was not different for the three muscle groups.
The bone percentages are in agreement with the findings of Berg and
Butterfield (1976), Schlegel (1979) and Hembree (1980). The percent age of bone varies with the percentage of fat and muscle. 30
TABLE 6. LEAST SQUARES MEANS (±SE) FOR CARCASS CHARACTERISTICS BY MUSCLE GROUPS
Muscle groups Characteristic Light Medium Heavy
de bide weight, kg 141.3 ± LK 4 159.3 ±5.5 153.0 ±4.2
Dressing percentage 62.1 -1. .6 63.8 8 62.6 ± .6
Quality grade 11.7 + .3 12.0 ± .4 11.5
Maturity 14.1 + .1 14.0 .1 l^i.O ± .1
Yield grade 2.6 + .2 2.8 2.5 ± .2
Fat thickness, cm 1.0 ± .1 1.1 1.0 ± .1
KPH fat, % 2.4 2.6 2.3
REA, cm^ 74.2 ±1.9 80.6 ±2.6 de 81.9 ±1.9 c d de 13.0 .5 13.8 + Conformation score 12.1 ± .4 Specific gravity 1.0473± .0022 1.0455± .0027 1.0481± .0020
Fat trim, % 17.4 ±1.1 17.6 ± 1.4 15.9 ± 1.1
Bone, % 15.4 ± .4 14.6 ± .5 15.3 ± .4
RCLT, %^ 63.2 ± 1.1 63.4 ± 1.4 65.0 1.0
a,c 10 = Gdo, 12 = Ch-
15 = A-, 14 = Ao.
'^eans in the same row with different superscripts are different (P<.05).
Boneless, closely-trimmed retail cuts plus ground beef. 31
Nonsignificant differences were found between muscling groups for quality grade. This would be expected of cattle of the same frame size that have been fed the same diet for the same length of time. No significant differences were found for carcass maturity when grouped by muscle.
Least squares means and standard errors for carcass character istics by trimness groups appear in table 7. No differences were
found in dressing percentage for the steers in the three groups.
Side weight was significantly larger for the mediimi and trim steers
than for the wasty steers.
Yield grade, FT and KPH fat were not different when the steers were grouped by trimness. Significantly larger REA were found for
the medium and trim steers than for the wasty steers. Conformation
score was significantly different for the three trimness groups with the trimmer steers having the highest scores, suggesting that
the muscling in trimmer steers was more readily identified in the
carcass. No differences were found in SG for the trimness groups.
The trim steers had the largest percent of RCLT although this dif
ference was not significant.
As with the muscle groups, percent bone did not differ between
the three trimness groups. These findings agree with those of Hembree
(1980).
Fat trim percentage tended to be lowest for the trim group of
steers; however, this difference was not significant.
Relationship of group with feedlot performance and carcass
characteristics. Simple correlation coefficients of feedlot per- 32
TABLE 7. LEAST SQUARES MEANS (± SE) FOR CARCASS CHARACTERISTICS BY TRIMNESS GROUPS
Trimness group Characteristic 'Wast y Med ium Trim Side weight, kg 131.8 ± 5.4^ 155.7 ± 3.3^ 153.0 ± 4.6^ Dressing percentage 61.5 ± .5 62.7 ± .5 63.5 ± .7 3, 11.8 ± .4 11.6 ± .2 11.9 ± .4 Quality grade Maturity 14.2 ± .1 14.0 ± .0 14.0 ± .1 Yield grade 2.8 ± .2 2.5 ± .1 2.7 ± .2 Fat thickness, cm 1.0 ± .1 1.0 ± .1 1.1 ± .1 KPH fat, % 2.4 ± .2 2.4 ± .1 2.4 ± .2 REA, cm^ 68.7 ±2.1 82.3 ± 1.3^ 79.4 ± 1.8^ c Conformation score 11.3 ± .4^ 12.9 ± .3^ 14.4 ± .4^ Specific gravity 1.0480± .0030 1.0469± .0018 1.0472± .0026 Fat trim, % 17.2 ± 1.6 17.1 ± 1.0 16.2 ± 1.4 Bone, % 15.4 ± .6 15.1 ± .4 15.2 ± .5 RCLT, % 63.2 ± 1.5 64.1 ± 1.0 64.2 ± 1.3
^'^10 = Gdo, 12 = Ch-. 15 = A-, 14 = Ao. Boneless, closely-trimmed retail cuts plus ground beef. ^'^'%eans in the same row with different superscripts are differ ent (P<.05). formance and carcass traits with muscle and trimness group are presented
in table 8. Muscle group was positively correlated with weight on test
(r = .53), average daily feed consumption (r = .45), and feed to gain
ratio (r = .39). As thickness of muscling increased, weight on test
and average daily feed consumption increased and feed efficiency de
creased.
Trimness group was positively associated with weight on test, weight off test and average daily feed consumption (r = .41, .41 and 33
TABLE 8. SIMPLE CORRELATION COEFFICIENTS OF FEEDLOT PERFORMANCE AND CARCASS CHARACTERISTICS WITH MUSCLE AND TRIMNESS GROUPS
Trait Muscle group Trimness group
Feedlot performance Weight on test .53** .41* Weight off test .31 .41* ADG .12 .31 Average daily feed consumption .45* .51** Feed/gain .39* .20 Fecal starch I -.29 -.05 Fecal starch II -.18 .07 Fecal starch III -.29 -.42*
Carcass characteristics Side weight .32 .42* Dressing percent .11 .33 Quality grade .07 .03 Maturity score .22 -.29 Yield grade .12 -.06 Fat thickness .10 .07 KPH fat •.08 -.00 REA .45* .45* Conformation score .52** .70** Specific gravity .06 -.03 Fat trim -.18 -.10 Bone -.04 -.04 RCLT, %^ .22 .08
^Boneless, closely-trimmed retail cuts plus ground beef. *r >.36, P<.05. **r ^.46, P<.01.
.51, respectively). These results indicate that the trimmer steers
were heavier in weight and ate more feed. Muscle or trimness group
was not significantly correlated with ADG.
Fecal starch III percentage was negatively associated with trim
ness group (r = -.42). The trimmer steers were more efficient in
starch digestion when this sample was taken; however, this is diffi
cult to account for because of the lack of difference among trimness 34 groups for ADG, feed to gain or measures of fatness.
Muscle group was positively correlated with REA and conformation
score. Trimness group explained 18% and muscle group 10% of the variation in carcass side weight. Muscle group and trimness group were positively associated with dressing percentage, FT and retail
cuts and lean trim (RCLT) percentage, but not to an extent to be of value for predicting carcass composition. Quality grade, maturity
score, yield grade, KPH fat, fat trim percentage and bone percentage were negatively associated with muscle group. Trimness group was
positively associated with side weight and REA (r = .42 and .45,
respectively). Trimness group explained 49% of the variation in
conformation score. Small negative associations existed between
trimness group and maturity score, YG, KPH fat, SG, fat trim percent
age and bone percentage. These results indicate that grouping cattle
by trimness or muscling is not a reliable indicator of their subse
quent performance and many carcass characteristics.
Conclusions. Feeder calves can be visually sorted into uniform
frame size groups as determined by skeletal measurements.
Feeder calves of the same frame size, age and sex exhibit uniform
QG when fed the same diet for the same length of feeding period.
Visual sorting according to muscling and trimness of the feeder
calves in this study did not result in consistent differences in feed
efficiency or starch digestibility. Although there was a tendency
for calves classed as heavily muscled and trim to produce carcasses
of higher cutability, the differences were either nonsignificant or
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