—V\—_‘— "—-—'v— .— __ _ THE ammonsmp 05 some SERUM HORMONES “TO VARIOUS GROWTH AND CARCASS CHARACTERISTICS OF CATTLE ‘ ' Thesis for the Degree of M. 8‘ ' MICHIGAN STATE UNIVERSITY JOHN STEVEN GRIGSBY 1973 i A 3 ‘AfAlLiJjgarl J; :ke be); Univcmfit ty m» M x ‘, ABSTRACT THE RELATIONSHIP OF SOME SERUM HORMONES T0 VARIOUS GROWTH AND CARCASS CHARACTERISTICS OF CATTLE by John Steven Grigsby The relationships of serum growth hormone (GH) and insulin to some growth and carcass characteristics were studied using 16 Hereford bulls, l7 Angus steers, 40 Holstein heifers, 19 Holstein steers and 13 Holstein bulls. The Hereford bulls were divided into two groups based on selection for either tenderness or leanness. Of the 40 Holstein heifers studied, 20 were fed 0.9 kg of grain daily and 20 were fed 4.5 kg of grain daily. Ten heifers from each nutritional level received 0.45 mg of MBA daily from 2.5 months of age. The Holstein steers were fed either 35% DM silage or 46% DM silage. Insulin and GH were quantitated by double antibody radioimmunoassays. Compositional data were obtained on wholesale rounds of Holstein heifers and 9-10-11 rib sections of Hereford bulls and Angus and Holstein steers. Tenderness was objectively determined using the Warner-Bratzler shear device and subjective measures of juiciness and overall acceptability were determined by taste panels. Angus steers had significantly (P s .05) lower daily gains and H01- stein steers had significantly higher (P s .05) daily gains during the bleeding period (ADGB) compared to the other breed and sex groups. Steers fed 35% DM corn silage had higher daily gains than those fed 46% DM silage. High nutrition as well as NBA treatment increased daily gains among Holstein heifers. Longissimus muscle areas (LMA) were not signifi- cantly different among the breed and sex groups but Angus steers had greater (P s .05) 12th rib fat thicknesses (FT-TH). Steaks from Holstein heifers were significantly (P s .05) more tender than steaks from the John Steven Grigsby other breed and sex groups. Taste panelists rated steaks of Angus steers more (P s .05) acceptable (0AA) than those of Holstein steers. Holstein steers had more lean and significantly more bone (P s .05) while Angus steers had significantly (P s .05) more separable fat than the other breed and sex groups. Among Hereford bulls, Angus steers and Holstein steers, FT-TH was negatively related (r = -.71, P s .01) to ADC and W-B shear values (r = -.28, P s .05) but positively related to 0AA (r = 0.36, P g .01). High levels of grain increased the fat component (P S .05) and MBA treatment depressed (P s .05) bone and W-B shear values among the Holstein heifers. Holstein steers had significantly (P s .05) higher average serum in- sulin (IN-A) while Holstein heifers had lower (P s .05) average serum GH concentrations (GH-A) than the other breed and sex groups. Bulls had lower (P S .05) GH-A levels than steers. Thirty five percent DM Pro-Sil (molasses, anhydrous ammonia and trace minerals) depressed serum GH compared to the 46% DM corn silage diet. Nutritional level among Holstein heifers had no influence upon plasma hormones but MGA treatment significantly increased IN-A. There were few significant correlations between either CH-A or IN-A and growth and carcass characteristics among individual breed and sex groups. In addition, hormone relationships with growth and carcass characteristics were generally inconsistent between breed and sex groups. However, when data of the individual groups were pooled, serum insulin was significantly and positively related to final weight (r = 0.26, P s .01), ADGB (r = 0.37, P s .01) and carcass weight (r = 0.38, P s .01). IN-A was not significantly related to any measures John Steven Grigsby of tenderness but generally was positively related to measures of lean and bone and negatively related to indices of fat. In contrast, GH-A was negatively related to daily gains (r = -.32, P s .01, total feeding period ADG; r = -.15, P > .05, ADGB) and Warner-Bratzler shear values (r = -.69, P s .01). Standard errors of hormone values within breed and sex groups were high and the relationships with growth and carcass variables were often inconsistent between individual groups. However, serum hormOnes were significantly related to a number of economically important growth and carcass characteristics. Insulin, compared to GH, was more highly related to a greater number of growth and carcass characteristics of feedlot cattle. THE RELATIONSHIP OF SOME SERUM HORMONES TO VARIOUS GROWTH AND CARCASS CHARACTERISTICS OF CATTLE by John Steven Grigsby A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Food Science and Human Nutrition 1973 ACKNOWLEDGEMENTS I would like to express sincere appreciation and thanks to Dr. R. A. Merkel, for his direction and support of this research and for his assis- tance in preparing this manuscript. The advflze and assistance of Dr. H. D. Hafs in the design of this experiment and in the development of hormone assay techniques is appreciated. Appreciation is expressed to Dr. R. W. Purchas for contributing data on the Holstein heifers used in this project. I also want to thank Drs. D. R. Romsos and H. D. Hafs for serving as members of my guidance committee. A special thanks goes to Dr. W. T. Magee for his patient assistance with the statistical analysis of these data. I appreciate the suggestions and assistance of Drs. A. Tucker, E. Convey and J. A. Koprowski and the use of equipment in the Dairy Physiology laboratory. I am extremely grateful for the association with and encour- agement of fellow graduate students and other staff members of the Meat Science Laboratory. I am indebted to my parents and to my brother and sister for their constant encouragement throughout my educational endeavors. Finally, I want to thank my wife, Kay, and son, Bricen, for their sacrifices, encouragement and inspiration throughout this work. ii TABLE OF CONTENTS INTRODUCTION . . . . . . . . . . . . . . . . LITERATURE REVIEW . . . . . . . . . . . . . Growth and Composition . . . . . . . . Bone Growth and Development . . Muscle Growth and Development . . Fat Growth and Development . Nutritional Effects . . . . . . . Sex Effects . . . . . . . . . . Breed Effects . . . . . . . . . . Age and Size Effects . . . . . . . Assessment of Growth and Composition . Tenderness . . . . . . . . . . . . . . Nutritional Effects . . . . . . . Age Effects . . . . . . . . . . . Sex Effects . . . . . . . . . . . Breed Effects . . . . . . . . . . Genetic Effects . . . . . . . . . Stress Effects . . . . . . . . . . Anatomical Location . . . . . . State of Contraction . . . . . . . Carcass Position . . . . . . . . . State of Rigor . . . . . . . . . . iii Page 12 13 14 15 20 20 21 23 25 26 26 28 28 29 30 Aging . . . . . . . . . . . . . . . . . . Connective Tissue . . . . . . . . . . . . . Protein Solubility . . . . . . . . . . Cold and Thaw Shortening . . . - . . . . - - Marbling . . . . . . . . . . . . . . . . . . Assessing Tenderness . . . . . . . . . . . . . . Hormones . . . . . . . . . . . . . . . . . . . . Fat Metabolism (Insulin) . . . . . . . . . . Fat Metabolism (Growth Hormone) . . . . . . Protein Metabolism (Insulin) . . . . . . . Protein Metabolism (Growth Hormone) . . . . Insulin and Its Control . . . . . . . . . . Growth Hormone Control . . . . . . . . . . . Relationship of Growth to Hormones . . . . . Relationship of Carcass Quality to Hormones Relationship of Body Composition to Hormones Melengestrol Acetate . . . . . . . . . . Diethylstilbestrol . . . . . . . . MATERIALS AND flTHODS . O O O i O O O O O C . C O O C 0 Experimental Animals . . . . . . . . . . . . . serm collection 0 O O O 0 C O C O C . O I I . Slaughter Procedures . . . . . . . . . . . . . iv Page 30 31 31 32 32 33 34 35 36 37 39 40 44 46 49 49 51 52 53 53 56 57 Page Measurement of Body Composition . . . . . . . . . . . . . . 58 Round . . . . . . . . . . . . . . . . . . . . . . . . 58 9-10-11 Rib Section . . . . . . . . . . . . . . . . . 58 Longissimus Muscle Area . . . . . . . . . . . . . . . 59 Fat Thickness . . . . . . . . . . . . . . . . . . . . 60 Quality Measurements . . . . . . . . . . . . . . . . . . . 60 Tenderness . . . . . . . . . . . . . . . . . . . . . . 60 Hormone Determinations . . . . . . . . . . . . . . . . . . 62 Radioimmunoassay for Growth Hormone . . . . . . . . . 62 Radioimmunoassay for Insulin . . . . . . . . . . . . . 62 Procedure of Insulin Assay . . . . . . . . . . . . . . 69 Calculation of Results . . . . . . . . . . . . . . . . 72 Statistical Analysis . . . . . . . . . . . . . . . . . . . 72 RESULTS AND DISCUSSION . . . . . . . . . . . . . . . . . . . . . 74 Growth Rates . . . . . . . . . . . . . . . . . . . . . . . 74 Carcass Characteristics . . . . . . . . . . . . . . . . . . 8l Hormones . . . . . . . . . . . . . . . . . . . . . . . . . 95 Relationship of Hormones to Growth and Carcass Character- istics . . . . . . . . . . . . . . . . . . . . . . . . 107 SUWIARY O O O O O O O O O O O O O O C O O O C I O O O O 0 O O O 1 2 0 LITERATURE CITED 0 O O O O O O I 0 O O O O I O O O O O O O O O O 123 APPENDIX 0 0 O O I O O O O O O 0 O I O O I O O O O O O 0 o O O O 142 Table 10 ll 12 13 14 15 16 LIST OF TABLES Experimental animals . . . . . . . Grouping of Holstein heifers according to treatment Grouping of Hereford bulls and Holstein steers according to treatment 0 O I O O O O O O O O 0 Various dilutions of GPABI and the corresponding percent 5I-insulin bound . . . . . . . . . Determination of percent insulin recovered Number, code and definition of variables Group number and description . . . . . Means and standard error of weights, ages and growth rates of various breed and sex groups . . Means and standard errors of growth traits of treatment subgroups within Hereford bulls, Holstein heifers and Holstein steers . . . . . . . . . . Means and standard errors of carcass traits of various breed and sex groups . . . . . . . . Simple correlation coefficients between some carcass traits of Hereford bulls, Angus steers and Holstein Steers 0 O O O O O O O O O O O O 0 0 Simple correlation coefficients between traits of Hereford bulls . . . . . . Simple correlation coefficients between traits of Angus steers . . . . . . . Simple correlation coefficients between traits of Holstein heifers . . . . . Simple correlation coefficients between traits of Holstein steers . . . . . Means and standard errors of carcass traits of treatment subgroups within Hereford bulls, Holstein heifers and Holstein steers . . . . . . . . . . vi some carcass some carcass some carcass some carcass Page 53 55 56 65 69 75 77 78 80 82 85 87 89 91 93 96 Table Page 17 Means and standard errors of growth, carcass and endo- crine traits of Holstein heifers . . . . . . . . . . . 98 18 Means and standard errors of serum growth hormone and insulin of various breed and sex groups . . . . . . . 99 19 Simple correlation coefficients between various hormone values 0 O O O 0 0 O 0 O 0 O O O O O I O O O O O O O O 104 20 Means and standard errors of serum insulin and growth hormone values of treatment subgroups within Hereford bulls, Holstein heifers and Holstein steers . . . . . 106 21 Simple correlation coefficients of some serum insulin values with various growth and carcass traits . . . . 108 22 Simple correlation coefficients of some serum growth hormone values with various growth and carcass traits 110 23 Simple correlation coefficients of some serum hormone values with various growth and carcass traits of EDI-Stein heifers O O O O O O O O O O O O O O O O O O O 111 24 Simple correlation coefficients of some serum hormone values with various growth and carcass traits . . . . 117 LIST OF FIGURES Figure Page 1 Dilution-response curve for guinea pig anti-bovine insulin set-Lulu O O O O O O I O O O I O O O C O O O O O O O O O 66 2 Dose-response curves for insulin standards and for ovine and bovine sera . . . . . . . . . . . . . . . . . . . 67 3 Recovery of exogenous bovine insulin added to 150 ul of bovine serum . . . . . . . . . . . . . . . . . . . . . 70 viii LIST OF APPENDIX TABLES Appendix Page I Composition of reagents used in radioimmunoassays . . . 142 II Raw Data 0 O O O O O O O O O O O O O O I O O O O O I O 147 ix INTRODUCTION The demand for red meat in the United States is rapidly increasing as evidenced by an approximate twenty two percent increase in per capita consumption of beef, pork, veal and lamb during the ten year period from 1961 to 1971. Although the efficiency of animal protein production is low compared to plant proteins, livestock producers have generally been able to meet the demand for their product. The ability of livestock pro- ducers to increase production efficiency while concomitantly increasing gross meat production is partially attributed to the use of various growth stimulants and antibiotics. Recently, both oral and implant administration of diethylstilbestrol (DES) have been prohibited. The ban on DES adminis- tration and the seemingly inevitable removal of other growth stimulants and antibiotics from livestock pharmaceutical markets may be attributed to their implication as possible human health hazards and pose a threat to present animal production efficiency. These facts indicate the tremendous need for animal scientists to understand basic physiological factors con- trolling growth, composition and meat quality. If such knowledge were available, it could possibly be used as a tool for selection or manipula- tion of growth and development criteria and; thus, may ultimately provide the basis of controlling carcass composition and meat animal production efficiency. It has been recognized for many years that hormones affect the physio- logical functions of animals. More recently, hormones have been shown to specifically affect or alter estrus cyclicity, sexual behavior, pubertal onset, growth, development, body composition and meat quality in animals. Therefore, it seems apparent that the endocrine system plays an extremely important role in meat animal production and that a thorough understanding of its functions may help to ultimately control or alter economically important factors in the production of muscle for food. The recent development of sensitive assay methods to quantitate endogenous hormone concentrations has provided animal scientists with a tool to study the relationships of circulating hormones to parameters im- portant in meat production. This study was initiated to determine the relationships of endogenous growth hormone and insulin with some growth, composition and meat quality characteristics among cattle differing in sex, breed and nutritional treat- ment. LITERATURE REVIEW Growth and Composition Growth rate and carcass composition are economically important fac- tors which contribute to the efficiency of production and ultimate useful- ness of meat animals. These two factors are interrelated as Hedrick (1968) noted that during growth and development an animal changes in form and composition. The rate and efficiency of growth as well as the factors affecting proportion of muscle, fat and bone in the carcass are current concerns of the animal scientist. His efforts to understand the mechanisms controlling these characteristics may allow him to ultimately use such information in manipulating body growth and/or composition. Attempts to define growth have been made by many workers who generally agree that growth is more than an increase in body size or weight. Brody (1945) defined growth as the production of new biochemical units brought about by cell division, cell enlargement or incorporation of materials from the environment, while McMeekan (1959) defined growth as an increase in weight until a mature size is reached. McMeekan (1959) also defined development as changes in body shape and/of conformation until the body structure and its various parts reach maturity. The inclusion of fat deposition into the definition of growth has met with controversy. Maynard and Loosli (1962) suggested that growth be defined as an increase in structural tissues and should be distinguished from fat deposition. In contrast, Pomeroy (1955) maintained that the distinction between growth and fattening was arbitrary and he could find no logical reason for ex- cluding fat deposition from the growth process. The major tissues of the animal body grow at relatively different rates postnatally (Hedrick, 1968). Hammond (1933) reported a triphasic growth pattern with maximum growth occurring sequentially, first bone deposition, then muscle and finally fat. Furthermore, body proportions change during development with certain anatomical locations developing faster than others. Wallace (1948) reported a gradient of increasing growth intensity in sheep with the lower limbs having maximum growth early and with late maximum growth occurring in the loin region. Luitingh (1962) studied the influence of fattening, age and nutrition on develop- mental changes in beef steers and observed the shoulder to be the slowest growing followed by the round, loin, plate, neck, brisket and finally by the fat depots, flank, cod and kidney fat. According to Palsson (1955) each tissue has a sigmoidal growth curve, but the inflection or point of maximal growth occurs at different ages for each tissue. He attributed the different rates of growth to nutrient priority by various tissues. The order of priority for nutrients of tissues from highest to lowest would be nervous tissue, bone, muscle and fat, respectively. Conforming to this hypothesis, early nutrient restric- tions would have a greater effect on fat than nervous tissue. However, as nutrients become increasingly available, a greater proportion of the available nutrients would be utilized by low priority tissues. The second inflection or point of growth rate deceleration of each tissue occurs at different ages and as each matures their demand for nutrients decrease correspondingly. Therefore, the observation that fat deposition occurs last among the major animal tissues can be explained by Palsson's hypothesis of nutrient priority. Bone Growth and Development. McMeekan (1959) suggested that bone completes a major portion of its growth early in postnatal life. Other workers have determined that the skeleton is better developed at birth than either muscle or fat (Allen, 1966). However, not all bones mature at the same time. Palsson and Verges (1952) measured the effect of various nutritional levels on body component growth in lambs and they observed that sheep on a low level diet early in life and a high level later had the heaviest rib weights. In a reanalysis of the Palsson and Verges data, Fowler ' (1968) suggested that the increase in rib weight may be explained by the function of the rib as a rigid container for the thoracic and anterior abdominal organs rather than the ribs being late maturing bones. The low-high nutritionally treated sheep had heavier thoracic organs and foregut weights; and thus, it follows that these organs would require a larger container. This agrees with the theory pro- posed by Fowler (1965) that an animal tends to respond to environmental changes in such a way that the vital functional relationships between essential body components are preserved or modified to a form which gives the animal its best chance of survival and successful reproduction. Cuthbertson and Pomeroy (1962) reported similar data with pigs and showed that increased weight was associated with increased thickening and ossi- fication of bone. Weiss _E._l. (1971) reported that bone decreased from 32 to 13 per- cent as body weight increased from 1 to 137 kg in pigs, suggesting that bone and body growth were not proportional. Zinn (1967) reported that the growth rate of bone decreased after 150 days on feed in both steers and heifers. Lambuth, Kemp and Glimp (1970) reported a higher percent bone among rapid gaining lambs (slaughtered at 36, 45 or 54 kg) as opposed to those which gained slowly. Muscle Growth and Development. Muscle is the major body tissue by weight (Hedrick, 1968) and its development is intermediate to that of bone and fat. Everitt (1963) indicated that muscle mass was dependent primarily on number, length and cross sectional size of muscle fibers and the associated connective tissues and to a lesser degree on other muscle components. Growth of muscle tissue is characterized by three distinct phases: in the first phase hyperplasia predominates and is followed by a phase of concurrent hyperplasia and hypertrophy and the final phase consists predominantly of hypertrophy (Winick and Nobel, 1965). Robinson (1969) noted that all these developmental stages are dependent upon an adequate substrate supply and that since the musculature is one of the later developing tissues it may suffer as a result of sub- strate inadequacy during cellular hyperplasia. He conducted an experi- ment with pigs involving three nutritional regimes. These regimes included a normal diet throughout pregnancy and lactation, half of the normal diet throughout pregnancy but normal during lactation and the third level con- sisted of half the normal diet during both pregnancy and lactation. He reported that nutritional stress during pregnancy had the least effect on ultimate muscle development, although muscle hyperplasia ceased earlier than in control animals. Nutritional stress during both pregnancy and lactation markedly decreased hyperplasia. Winick and Nobel (1965) noted that tissues are most susceptible to nutritional stress during active hyperplasia and that the effects of severe stress may be irreversible during this stage. The continuation of postnatal hyperplasia disagrees with McMeekan's (1940) suggestion that muscle fiber number is fixed at birth. Most postnatal increase in muscle mass occurs by hypertrophy. Chry- stall, Zobrisky and Bailey (1969) reported a 100 percent increase in muscle fiber diameter from birth to 25 days of age in pigs and only a 10 percent increase from 100 to 125 days. At 150 days, fiber diameter increase was 95 percent complete and after 150 days muscle growth was extremely slow. McMeekan (1940) observed that the coefficient of variation of the longissi- Egg muscle fibers decreased from 44 percent at birth to 25 percent at 28 weeks of age, during which time fiber diameter increased eight fold. Chrystall _£ El. (1969) found that age and weight of pigs were significantly correlated (P < .01) with and accounted for 64 and 72 percent, respectively, of the variation in muscle fiber diameter. Furthermore, they reported correlation coefficients of 0.85 and 0.92 between longissimus muscle area and age and weight, respectively. In this same study protein content did not increase proportionally with the increase in muscle fiber diameter. Swatland and Cassens (1972) studied muscle enlargement in two lines of rats selected for rapid and slow postweaning weight gain and reported greater mean muscle fiber diameter among the rapid gaining rats than for those with slow gains. Brody (1945) noted that during rapid growth fiber diameter increased but the increment in fiber size became progressively less as growth slowed and mature size was attained. Yeats (1964) observed a decrease in cross sectional area of bovine lopgissimus muscle following starvation and attributed it to muscle fiber atrophy and loss of intramuscular fat. He suggested that the connective tissues were relatively unaffected. Subsequent regain of live weight resulted in recovery of whole muscle dimensions and muscle fiber diameters. Thus, it would appear that inadequate nutrition irreversibly affects hy- perplasia while the effect on hypertrophy is reversible. Fat Growth and Development. According to Palsson (1955), fat has the lowest nutrient priority during early development and therefore, it is the latest of the three major tissues (bone, muscle and fat) to develop. During growth and development, fat mass increases by hyperplasia and hyper- trophy. Kirsch (1969) reported that the early growth of fat depots in rats was accompanied by progressive enlargement of fat cells as well as by an increase in cell number. However, during late growth, the increase in fat mass was due entirely to hypertrophy. Hood (1972) showed that during early growth mass of adipose tissue increased by hypertrophy and hyper- plasia in bovine and porcine animals. However, in pigs beyond 20 weeks of age, adipose tissue growth occurred exclusively by hypertrophy. He noted that in young animals, growth rate was positively correlated with adipocyte number but unrelated to fat cell number in more mature animals. By 14 months of age, hyperplasia was completed in all bovine fat depots except the late developing intramuscular adipose tissue. Hood (1972) fasted 109 kg pigs to produce weight losses of 32 kg and reported a significant decrease in fat cell size among both lean and fat strains. In the lean pigs, cell number remained unchanged while in the fat pigs, hyperplasia continued during the fasting period. He suggested that the fat strain had not yet attained maximum cell numbers prior to the onset of fast; and therefore, hyperplasia continued until the ultimate adult cell numbers had developed. Hedrick (1968) indicated that rates of fat deposition in different parts of the body vary widely. The sequence of fat deposition showed that the initial deposit occurs around the viscera and kidney followed by inter- muscular fat, subcutaneous fat and finally intramuscular fat. Nutritional Effects. Nutrition contributes significantly to animal growth and body composition. During gestation, fetal nutrient supply is completely dependent upon the maternal supply of nutrients. Robinson (1969) restricted sows to low levels of nutrition during gestation which resulted in an early cessation of myohyperplasia in their offspring. He stated that nutritional stress imposed at birth caused permanent stunting in tissues in a manner directly pr0portional to their order of development and related to the degree of active hyperplasia proceeding at the time of stress. Ahlschwede and Robison (1971) studied the influence of pre- and postrntal environments on growth and backfat in pigs. Prenatal effects contributed approximately 17 percent of the variance in postweaning growth and backfat while postnatal effects only accounted for 11 percent of the variance. Robinson (1969) reported that growth generally, and in muscle specifically, was much slower in pigs from sows on restricted feeding during pregnancy and lactation compared to those from sows on normal diets during lactation. In addition, pigs subjected to nutritional stress during active hyperplasia reached the same body weight but had a greater proportion of fat than ani- mals on normal diets. lO Berg and Butterfield (1968) indicated that the major tissues of the bovine carcass show differential growth during development and that nutri- tional levels affected tissue growth. They noted that semistarvation depleted fat and decreased muscle deposition with only minor bone depletion. Realimentation restored the normal muscle and bone ratios and the propor- tion of fat was related to the plane of nutrition and length of the com- pensatory feeding period. Carr, Allen and Phar (1971) could not show any depletion of intramuscular fat in the longissimus muscle of fasted steers. Moulton, Trowbridge and Haigh (1922) observed greater percentages of muscle and higher muscle to bone ratios as the level of nutrition increased in steers. Kelly _£._l. (1968) reported increased fat percentages and de- creased bone in cattle as the amount of grain in the diet was increased. Henrickson, Pope and Hendrickson (1965) observed that cattle on a high nutritional level during the last half of the total feedlot gain had 2.8 percent less muscle, 4 percent more fat and 0.8 percent less bone than those fed a moderate level. On a constant weight basis cattle on the moderate nutritional level during the last half of their feedlot gain re- quired 65 days longer to reach slaughter weight. They concluded that the major differences in carcass composition resulted from the level of nutri- tion during the last half of the feedlot gain period. Similar results were reported by Waldman, Tyler.and Brungardt (1971). The type of diet has also been shown to affect composition. Garrigus _£._l. (1967) and Johnson _£__l. (1967) observed increased carcass fat when a corn concentrate diet was fed, especially in the later stages of the feeding period, as compared to hay or corn silage diets. Davey and Morgan 11 (1969) fed either a 12 percent or 20 percent protein diet to pigs selected for high or low backfat. On a 20 percent protein diet, the lean strain pigs had 36 percent more muscle and the fat strain had 11 percent more muscle than those fed 12 Percent protein. In both lines of pigs, the 20 percent protein diet significantly increased average daily gain but had no effect on longissimus muscle area. During the feeding period of beef, (up to 341 kg) muscle weight increases rapidly while bone and fat deposition is slow. From 341 kg to 590 kg bone and muscle weights increase proportion- ally (Waldman, Tyler and Brungardt, 1971) but fat deposition accelerates between 227 kg and 341 kg. Zinn (1967), Stringer _£.§l- (1968) and Hedrick, Thompson and Krause (1969) reported increased fat and decreased retail yields as the length of the feeding period increased. The longissimus muscle area increased but the increase was not proportional to carcass weight. In addition, rate of gain tended to decrease as time on feed in- creased (Stringer _£__l., 1968). Anderson, Fausch and Gesler (1965) fed pigs on three nutritional regimes as follows: 1) ad libitum, 2) one--two hour period per day and 3) two-~one hour feeding periods per day. Pigs allowed to eat twice daily for one hour had less backfat, lower ham weights and smaller longissimus muscles than ad libitum fed pigs of similar weights. However, pigs fed twice daily (two--one hour feedings) had more backfat than those fed only once daily. Ad libitum fed pigs consumed 27 percent more feed but gained 27 percent more weight than pigs allowed to eat only once daily for two hours. 12 Sex Effects. Sex, whether determined at conception or as a result of castration after birth, influences beef carcass composition (Hedrick, 1968). It is generally accepted that, at given weights, bulls have less fat than steers and steers have less fat than heifers. Hankins and Howe (1946) studied the composition of 84 steers and 36 heifers and reported 23.8 and 29.2 percent fat, 58.3 and 55.8 percent muscle and 18.0 and 18.1 percent bone for steer and heifer carcasses, respectively. Bailey, Probert and Bohman (1966), Pearson (1966), Hedrick (1968), Arthaud t al. (1969), Hedrick _£__1. (1969) and Field (1971) all reported higher percents of muscle or percents of retail cuts and lower percents of fat from bull than steer carcasses. Hedrick (1968) reported that steers have greater fat thickness and more total separable fat but less kidney fat than bulls. Hedrick _£__l, (1969) reported that bulls exceeded steers and heifers in rate of gain but that steers and heifers had similar gain rates. In addi- tion, bulls had larger longissimus muscles and less fat than steers or heifers while steers and heifers were remarkedly similar. Steers had higher percents of retail cuts than heifers. Bailey g£__l. (1966) reported 31 and 40 percent fat, 52 and 44 percent muscle and 17 and 16 percent bone for bulls and steers, respectively. They also noted that bulls and steers were similar in preweaning growth rate but that bulls grew more rapidly and were more efficient in the feedlot than steers. On a weight constant basis, bulls yielded 13.2 kg more retail products than steers and on an age constant basis bulls yielded 26.8 kg more boneless retail cuts than steers (Arthaud t 1., 1969). t al. (1969) castrated bulls at birth, 2 months, 7 months Champagne and 9 months of age and they observed less fat over the longissimus muscle 13 of bulls compared to steers, except for those castrated at 9 months. Differences in fat among the 2 and 7 month castrates were not significant. The longissimus muscles of castrates were not significantly different from each other but tended to increase with increasing age at castration. Bull carcasses had significantly more longissimus muscle area and yielded more boneless retail cuts than any group of castrates. Breed Effects. In general, most studies involving breed effeCts on carcass composition have compared beef and dairy cattle or crosses of various breeds. Carrol, Rollins and Ittner (1955) and Riggs and Maddox (1955) compared Hereford and Hereford X Brahman steers and reported that Herefords had less bone, more fat and less muscle than crossbred steer carcasses. Carpenter ~£_~l. (1961) reported a decrease in percent fat and an increase in percent muscle as the percent Brahman breeding increased in Brahman X Shorthorn steers. Cole _£__l. (1964) compared carcasses froux Hereford and Angus, Brahman and Santa Gertrudis and Holstein and Jersey steers. British breeds yielded more fat and less separable muscle than Zebu or dairy breeds while percent separable bone was greatest in cattle of dairy breeding. Angus carcasses had the lowest percent separable muscle and bone but the highest percent separable fat while Holstein carcasses had the lowest percent fat and highest percent muscle and bone. Branaman _£‘_l. (1962) compared carcasses from Hereford and Holstein steers and found no significant differences in percent separable muscle or fat, but dairy steers had significantly higher percentages of bone. Hedrick (1968) reported that dairy breeds have higher percentages of kidney and pelvic fat but lower subcutaneous fat percents than beef breeds. Klosterman, l4 Cahill and Kunkle (1961) and Cahill, Klosterman and Ockerman (1962) re- ported higher percentages of trimmed retail cuts and lower fat percents in Charolais carcasses compared to Herefords. Not only do breeds differ in composition, but strain differences within breeds are also apparent. For example, Davey and Morgan (1969) selected pigs for high and low fat and were able to produce pigs in the fat line with 9.1 percent less muscle, 11.7 percent more fat and 2.5 per- cent less bone than the lean line. Age and Size Effects. The growth and development of various tissues reflects the effect of age on composition. In a review, Hedrick (1968) indicated that, generally, rapid muscle and bone growth at an early age was followed by an acceleration of fat deposition with a concomitant slowing of muscle and bone growth. In addition, he reported that growth rate was more rapid early in life and became slower as maturity was approached. However, he noted that most available data indicated that weight and stage of fattening had a greater effect on composition of the carcass than age pg; £2! Weiss _£‘al. (1971) slaughtered pigs at various live weights. In general, the percentages of muscle and bone decreased and separable fat increased significantly as slaughter weight increased. They also reported a significant weight-by-body section interaction which conformed to the growth pattern of rapid muscle deposition early in life followed by an increase in fat deposition with advancing maturity. They observed a progressive anterior toposterior pattern of muscle development. Hiner (1971) compared pigs at various weights and reported that the three major carcass components increased as weight increased. However, the 15 ratio of lean to fat decreased as live weight increased from 56.7 kg to 124.7 kg. Lambuth, Kemp and Glimp (1970) and Shelton and Carpenter (1972) compared lambs at several live weight intervals and found that percent boneless retail cuts and bone decreased while percent fat increased as weight increased. Hedrick _E.il° (1969) compared animals at 400 and 500 kg live weight and reported that extended feeding resulted in decreased retail cut and bone percentages and increased fat trim in bulls, steers and heifers. Waldman _£.il- (1971) found that the increases in fat and bone were small compared to muscle during early growth in steers. At approximately 227 kg, fat deposition accelerated and paralleled muscle deposition through 590 kg live weight. Allen _£‘_l. (1968) studied the effect of carcass weight on composition in eighty steer carcasses divided into two weight groups (227 to 250 kg and 318 to 340 kg). The light weight group yielded 51.7 percent muscle, 35.5 percent fat and 11.4 percent bone compared to 50.8, 37.0 and 11.2 percent muscle, fat and bone, respectively, in the heavy weight group. Carcass weight significantly (P < .01) affected the weight of separable muscle, fat and bone but the percentages of sep- arable components were not significantly different between the two weight groups. The light weight carcasses yielded higher percentages of retail cuts than the heavy weight groups. Assessment of Growth and Composition Available methods of measuring growth and composition were reviewed by Hedrick (1968) and Pearson (1968). They indicated that only a relatively small percentage of actual variation in retail cuts could be accounted for 16 by subjective estimates on live animals and that precise objective measures are needed for selection of carcass traits. Pearson (1968) noted that, even though there is some relationship between certain linear measurements on the live animal and some carcass traits, these relationships are not high enough to be used for predicting carcass composition or other meaning- ful criteria. He also stated that weight pg£_§g is a more accurate pre- dictor of composition and cutout than most linear body measurements. It appears that the most accurate method of estimating total carcass composition involves the physical separation of fat, muscle and bone from the entire carcass; however, portions of the carcass have been used to compare differences in composition. The most widely used of these portions is the 9-10-11 rib section, followed by the wholesale round and wholesale flank. Lush (1926) and Hopper (1944) concluded that muscle, fat and bone of the wholesale rib adequately represented their respective components in the entire carcass. Hankins and Howe (1946) studied data from 84 steer and 36 heifer carcasses by comparing physical separation of fat, muscle and bone from the 9-10-11 rib section with that of the total carcass. They concluded that a high association existed between physically separable components of the 9-10-11 rib section and those of the entire carcass. Correlation coefficients between separable components of the rib section and the total carcass were 0.93, 0.85 and 0.83 for fat, muscle and bone, respectively, from the 120 carcasses. The correlation coefficient of muscle from the rib section and total carcass muscle was higher for steers (0.90) than heifers (0.72) which led Happer (1944) to conclude that the usefulness of the 9-10-11 rib separable muscle content for estimating total 17 carcass muscle of heifers was questionable. The separable fat of the rib 'section was more highly correlated (0.93) with separable fat of the dressed carcass in steers compared to heifers (0.88) (Hankins and Howe, 1946). When. ether extract and protein determination of the dressed carcass were compared to separable fat and muscle of the 9-10-11 rib section, correla- tions of 0.93 and 0.82, respectively, were obtained. Crown and Damon (1960) reported correlation coefficients of 0.98, 0.94 and 0.73 for sep- arable fat, muscle and bone of the 9-10-11 rib section and corresponding components of the entire carcass. Likewise, Allen (1966) reported corre- lation coefficients of 0.92, 0.94 and 0.76 for muscle, fat and bone, respectively, from the 9-10-11 rib section and the entire carcass. He reported lower correlations in heavy cattle (700 to 750 lb) compared to light cattle (500 to 550 lb); therefore, Hedrick (1968) concluded that a need exists for prediction equations to be developed for well defined weight, sex and fat groups for more accurate results. Powell and Huffman (1968) compared five methods to estimate carcass composition and concluded that the Hankins and Howe method most accurately estimated carcass fat (r = 0.94) and carcass protein (r = -.96), however, it was the least practical method studied. A number of workers have reported high correlations of separable components of the wholesale round with those of the entire carcass. Hedrick (1968) noted that since the round comprises a sizeable portion of the carcass, it should be a good indicator of total carcass composition. Allen (1966) reported correlation coefficients of 0.83, 0.91 and 0.83 between percent separable muscle, fat and bone, respectively, of the round 18 and percent separable components of the entire carcass. Cole, Orme and Kincaid (1960) noted that separable muscle in the round was associated with 90 percent of the variation in total separable muscle in the carcass. Hedrick (1968) concluded that research reports to date are rather con- sistent in the finding that trimmed round or boneless closely-trimmed retail cuts from the round are indicative of the retail yield of the entire carcass. He also noted that compositional data from the round would result in minimum economic losses and would provide adequate informa- tion for development of an equation to predict retail yield from beef carcasses. Palsson (1955), Luitingh (1962) and Butterfield (1965) have shown that the flank can be used to estimate carcass composition. Hankins and Howe (1946) reported a higher correlation between ether extractable flank fat (r = 0.95) than that of the 9-10-11 rib section (r = 0.93) and total carcass fat. They also reported a correlation coefficient of 0.89 between ether extractable flank fat and fat from the 9-10-11 rib cut. In addition, Allen (1966) observed correlation coefficients of 0.91, 0.91 and 0.32 between percent separable muscle, fat and bone, respectively, of the wholesale flank and separable components of the entire carcass. The low correlation observed for bone is expected since the flank con- tains only a small portion of the 13th rib (Purchas, 1969). Purchas (1969) indicated that the flank should be at least as effective as the round for estimating carcass fat but would probably not be as good an indicator of muscle or bone as the 9-10-11 rib section or wholesale round. The cross sectional area of the longissimus muscle is often used as a measure of total carcass muscle. Cole, Ramsey and Epley (1962) reported l9 correlation coefficients of 0.58, 0.59, 0.39 and 0.63 between total separ- able muscle and the longissimus muscle area at the 5th rib, 12th rib, last lumbar vertebra and an average of these three area measurements, respectively. Hedrick _£_al. (1965) noted that longissimus muscle area accounted for 48 to 70 percent of the variation in weight of boneless retail cuts. Similarly, longissimus muscle area measurements accounted for 49 to 69 percent of the variation in boneless retail cuts of the entire side. In contrast to these observations, Epley £3 1. (1970) concluded that longissimus muscle area was of little value in estimating percent retail cuts of the four major wholesale cuts. Fat is the most variable component of the beef carcass and since there is an almost proportional decrease in muscle as percent fat increases, many workers have studied the relationships of fat measurement to carcass composition (Hedrick, 1968). He indicated that fat thickness over the 12th rib was more highly associated with total carcass fat than any other anatomical fat measurement. Ramsey, Cole and Hobbs (1962) reported correlation coefficients of -.76, 0.83 and -.76 between fat thickness over the 12th rib and percent separable muscle, fat and bone, respectively. Nelms _£H_1. (1970) reported that fat thickness over the 12th rib made a significant contribution to an equation for predicting retail cuts. Like- wise, Powell and Huffman (1968) reported correlations of 0.89 with carcass fat and -.85 with carcass protein and they indicated that over 70 percent of the variation in carcass composition was accounted for by the fat measurement over the 12th rib. 20 Tenderness Tenderness has been shown to be the most important quality factor contributing to consumer acceptability of meat (Brady, 1957; Rhodes _£._l., 1958; Means and King, 1959; Juillerat and Kelly, 1971); however, the range of tenderness acceptable to consumers is rather wide (Pearson, 1966). Tenderness is affected by pre- and postslaughter conditions. Before slaughter, anatomical and environmental factors combine to influence ten- derness while after slaughter physiological factors and physical handling procedures are important contributors to meat tenderness. The relative importance of tenderness to the meat industry necessitates an indepth study of factors contributing to tenderness and an attempt to control or alter meat tenderness in all species of meat animals. Nutritional Effects. Information regarding the effects of nutrition on tenderness is limited. In a review of work involving different nutri- tional regimens, Stringer (1970) noted that low protein diets for pigs were associated with increased marbling and tenderness. Purchas (1969) found nonsignificant differences in tenderness of steaks from Holstein heifers fed either high or low levels of nutrition although those fed high levels tended to have higher Warner-Bratzler shear values. Dube ££ al. (1971) reported that steaks from animals fed corn silage during the early part of the feeding period were more tender than those from hay fed animals. The differences in palatability due to the early feeding regimen were Still evident at heavier weights and they noted that palatability was influenced less by the feeding regimen midway into the feeding period 21 than it was early in the feeding period. When animals of comparable age and of the same sex were slaughtered at 30 day intervals over a 270 day feeding period, Zinn gg‘al. (1970) showed that the first 180 days on feed had a beneficial effect on tenderness and that shear values were lower at 150 and 180 days on feed than at all other periods. Animal age appeared to exert a greater influence after 180 days and an interaction between time on feed and animal age was apparent. Zinn _£’al. (1970) also reported that tenderness of all muscles was not affected equally by certain dura- tions of feeding. Tenderness may be dramatically affected by the nutritional state of the animal just prior to slaughter. Zessin _£H_l. (1961) showed that pigs on a submaintenance diet had less intramuscular fat in the longissimus muscle than pigs on a fattening diet and that roasts and chops from fasted pigs were less tender than those from pigs on a fattening diet. Further- more, Lewis, Brown and Heck (1965) concluded that limited feeding increased shear values. In a review, Hedrick (1965) referred to work involving sucrose feeding immediately prior to slaughter and noted that pigs on a high sucrose ration had pale, soft and watery muscles which were less tender than controls. In contrast, Mellor, Stringer and Mountney (1958) reported that feeding broilers sugar prior to slaughter increased the glycogen level of the muscle and improved tenderness of the pectoralis minor muscle. Age Effects. Although most animals are marketed at a relatively early chronological age, there are some animals which, due to environmental or 22 genetic growth potential, are marketed at advanced ages. Dunsing (1959) reported that consumer panels consistently favored steaks from younger animals and in a review, Pearson (1966) concluded that the degree of maturity of an animal appears to have a definite influence on tenderness, although tenderness is not greatly altered within a narrow age range. Hiner and Hankins (1950), Tuma t l. (1962), Tuma et 1. (1963), Goll t l. (1965), Bre idenstein ___t_ __l_. (1968) and Webb, Kahlenberg and Naumann (1964) agreed that tenderness decreases with advancing maturity. On the other hand, Ritchey and Hostetler (1964), Romans _5 a_1_. (1965) and Champagne t al. (1969) found no significant relationship between animal age and tenderness. In contrast, to both of these concepts, Alsmeyer _t;_l. (1959) and Field, Nelms and Schoonover (1966) reported positive correlations between age and tenderness in some animals. Two possible explanations for these conflicting data may be that in some cases wide ranges in age are studied while in others only narrow ranges are tested or perhaps physiological age may be quite different from chronological age as suggested by Webb t al. (1964). Champagne _£ _1. (1969) did not find any significant differences in Warner-Bratzler shear values of steaks from steers and bulls between birth and nine months of age. They also reported that differences in carcass characteristics attributable to castration age were, in most cases, nonsignificant. Likewise, Ritchey and Hostetler (1964) reported no clear cut evidence of age effects on tenderness in animals between 33 and 62 weeks old. Dissimilarly, Helser, Nelson and Lowe (1930) and Simone, Carroll and Chichester (1959) noted that cattle finished at 18 months of age were more tender than those finished at 30 months of age. 23 Reagan _t_ 531. (1971) obtained similar results when they compared bulls and steers at 385 and 484 days of age. Hiner and Hankins (1950) concluded that tenderness decreased with age in cattle between 2.5 and 66 months of age . Field _t_ a_1_. (1966) reported that when marbling was held constant, bulls 300 to 399 days old were significantly more tender than bulls 400 to 699 days old. However, they could find no significant tenderness dif- ferences among bulls after 400 days of age. In contrast, they found a significant positive correlation between age and tenderness in heifers and steers. Zinn _t_ _1_. (1970) found a significant interaction. between number of days on feed and animal age. They reported that cattle on feed 180 days were more tender than those fed for 270 days, at which time, age of the animal had a greater influence on tenderness than number of days on feed. Hunsley _e_t_ 11. (1971) compared shear values of cattle slaughtered at 6, 9, 12, 15 and 18 months of age and reported cattle. at 6 and 18 months were more tender. Arthaud _t _l. (1970) reported similar results. Sex Effects. Extensive data have been compiled on the influence of SEX on tenderness. Such extensive work has been prompted by the well known facts that bulls grow faster than steers or heifers, are leaner, more efficient and have larger longissimus muscles and that steers are leaner tlhan heifers at equal weights and are easier to manage than either bulls or heifers. However, most of the beef produced in the 0.8. for the fresh meat trade is from steers and heifers because of the concensus that bull beef has inferior quality (Hedrick a a_1_., 1969). Consumer acceptance ratings for loin steaks from young bulls have been lower than those for steers 24 (Field, Schoonover and Nelms, 1964), however, 90 and 88 percent of consumers who bought steaks and roasts, respectively, from bulls said they would buy them again. Shelton and Carpenter (1972) could not show any significant differences in shear values between rams, wethers and ewes slaughtered at weights ranging from 36 to 64 kilograms. Hedrick t 1. (1969) showed no significant differences in‘Warner-Bratzler shear values of steaks from bulls less than 16 months of age and steers and heifers of comparable chronological age. However, shear values of steaks from more mature bulls were greater than those from steers or heifers at the same age. Warwick fig a_1_. (1970) also reported nonsignificant differences in Warner-Bratzler shear values when monozygotic male twins were paired and fed as a bull and a steer and slaughtered at an average weight of 408 kilograms. Champagne 21; __l. (1969), likewise, reported no significant differences in tenderness ratings between steaks from bull and steer carcasses. In contrast, Arthaud _i _l. (1970) reported significant shear value differences between Steaks from bulls and steers. Field t l. (1966), Hedrick gt 1. (1969), Hunsley _g _l. (1971) and Reagan t l. (1971) also reported significant differences between shear values of steaks from bulls and steers. The data available indicate that differences in tenderness attributed to sex may actually be due to a sex x age interaction. Zinn t l. (1970) in a study involving both sex and age variables reported that muscles from heifers were more tender at 150 days on feed (P < .05) while steer muscles were more tender (P < .05) at 240 days. He suggested that the heifers may have matured at an earlier age reaching a peak tenderness about 30 days eal‘lier than steers. That heifers mature at an earlier chronological age 25 was reported by Gramlich and Thalmann (1930) and Hankins (1932). Field t _l_. (1966) studied relationships of tenderness with sex and age in bulls, steers and heifers ranging in age from 300 to 699 days. They found no significant differences between bulls or steers and heifers between 300 to 399 days old. However, steers and heifers 400 to 499 days old had slightly higher palatability scores (more acceptable) than bulls of similar ages and shear scores indicated that bulls 500 to 599 and 600 to 699 days old were tougher (P < .01) than steers and heifers of comparable ages. Data presented by Hedrick _£ __1_. (1969) indicated that chronological age may have a greater adverse effect on tenderness of steaks from bulls than from steers or heifers. Although Field t l. (1966), Arthaud t1. (1969) and Reagan __t __l_. (1971) concluded that variation in tenderness of steaks from bulls is considerably greater than steers and heifers, it appears that when animals are slaughtered at a reasonably young age there would be little consumer discrimination against any sex group in tenderness. Breed Effects. Alsmeyer et a1. (1958) working with Brahman, Shorthorn and various crosses reported that differences in tenderness due to breed of sire were significant. They showed that steaks from Shorthorn progeny were on the average more tender than steaks from progeny of Brahman and crossbred sires. However, they also reported that offspring from some Brahman bulls produced more tender meat than some of the British breeds. Kincaid (1962) showed that tenderness as measured by shear force decreased as the percent Brahman decreased. A very extensive comparison of tender- ness among various breeds was conducted by Ramsey t al. (1963)- Among 26 three types of cattle (British, Zebu and dairy breeding), loin steaks from dairy steers were more tender and Jersey steers showed the greatest tenderness. Loin steaks from British and dairy breeding were not signi- ficantly different in tenderness. Branaman _£‘_l. (1962) also reported no significant differences in tenderness between young beef and dairy type cattle. In addition, Ramsey 25 _l, (1963) reported that steaks of steers from Brahman breeding were significantly less tender than steaks of steers from British or dairy breeding. In their studies, there were no significant tenderness differences in steaks from Hereford, Angus, Holstein or Jersey breeds. Pearson (1966) suggested that conformation or type has little to do with tenderness even though some differences have been reported between breed types. Genetic Effects. Evidence that tenderness can be selected for is provided by Field _£._l- (1970). They made direct selection for either tenderness or leanness in two lines of Herefords for eleven years and found that significant differences in tenderness did exist between the two lines of Hereford bulls. Stress Effects. Selye (1950) noted that animals exposed to a variety of stress factors reacted with an increased secretion of hormones from the adrenal gland which in turn affected the levels of muscle glycogen at the time of slaughter. Webb t l. (1959) and Webb, Kahlenberg and Naumann (1964) showed decreased tenderness in animals stressed with adrenalin in- jections prior to slaughter. Hedrick t 1. (1959) observed that exogenous adrenalin injections reduced muscle glycogen in all animals studied. Low 27 levels of glycogen at slaughter limit the extent of lactic acid formation and hence results in increased postmortem muscle pH. The high pH of postmortem muscle is responsible for "dark-cutting" meat. Hedrick _£‘_l. (1959) reported nonsignificant differences in ten- derness between normal and dark-cutting beef. Loeffel (1942) reported that dark-cutting beef had lower shear values than normal beef and Lawrie (1962) indicated that the lowest tenderness scores for beef were obtained at pH 5.8 to 6.0 and the most tender meat was found at about pH 7.0. The condition of pale, soft and exudative (PSE) muscle is the result of the preslaughter stresses on susceptible pigs. In PSE muscle, lactic acid formation occurs very rapidly postexsanguination (Judge, 1969) thereby allowing muscle pH to decline while body temperature is still high. The rapid formation of lactic acid may be enhanced by the scalding procedure and high adiposity whereby the insulating effect of fat maintains near normal or slightly elevated temperatures. Carpenter (1961), Sayre t l. (1961), Lewis, Heck and Brown (1963) and Kauffman _E'al. (1964) reported normal muscle to be more tender than PSE muscle. In contrast, Judge 25 31. (1958, 1960) and Merkel (1971) showed tenderness to be greater in PSE muscle. Hedrick (1965) reviewed the available literature and concluded that when cattle and lambs were subjected to stress conditions just prior to slaughter they usually had lower muscle glycogen, higher postmortem muscle pH and improved tenderness while pigs subjected to certain stress conditions generally had lower postmortem muscle pH and were less tender than muscle from normal animals. More recently, however, Merkel (1971) presented contrasting results for pigs. 28 Anatomical Location. Not only does tenderness vary from animal to animal but it also varies between different muscles within an animal. Briskey and Kauffman (1971) reported that connective tissue content was greater toward the distal region of a limb and that tenderness was nega- tively associated with the quantity of connective tissue. Knutson _£_§1, (1966) divided carcasses into the loin region, sirloin region and rear quarter region. Averages of muscles within these three groups showed decreasing tenderness in the order from loin region to rear quarter region, respectively. The most tender muscle measured was the longissimus and the toughest was the biceps femoris. Zinn t al. (1970) also reported a sig- nificant effect of muscle location on tenderness. In their study they attributed the low shear value of the triceps brachii and the high shear resistance of the longissimus to the variation in physiological maturity of the muscles, since it had been reported that the longissimus was more mature than the triceps brachii at comparable chronological ages. State of Contraction. The state of muscle fiber contraction influences tenderness. Locker (1960), Herring, Cassens and Briskey (1965) and Herring _E‘gl.(1967a) have reported that muscles allowed to contract such that fiber diameter increased and sarcomere length decreased were less tender than stretched muscles with long sarcomeres and narrow fiber diameters. Herring g£_al.(l967a) reported fiber diameter to be linearly related to tenderness while sarcomere length was curvilinearly related to tenderness. In contrast, Covington t l. (1970), Field t l. (1970) and Hunsley g£_ El. (1971) reported no significant relationship of fiber diameter and/or 29 sarcomere length with tenderness. However, Gothard _£__l. (1966) reported that the state of contraction after 7 days aging appeared to have a greater influence on tenderness than did state of contraction at time of maximum rigor mortis. They concluded that although contraction did not seem to be the factor most responsible for final tenderness, it appeared to have a significant influence. Carcass Position. The recent information regarding the effects of contraction state on tenderness prompted several workers to study the relationship of carcass position before and during rigor mortis with tenderness. The normal procedure is for carcasses to be suspended by the Achilles tendon which, in general, tends to stretch muscles anterior to the femur but allows those posterior to the femur to shorten. Herring g5 al. (1965) hung right sides according to the normal procedure but left sides were placed horizontally, bone down, on a flat surface with the limbs fixed perpendicular to the long axis of the carcass. In the vertical posi- tion, sarcomere length and tenderness was greater in the psoas major, latissimus dorsi and rectus femoris. Muscles with greater tenderness and longer sarcomeres in the horizontally positioned carcasses were the longissimus, gluteus medius, adductor, biceps femoris and semitendinosus. Fiber diameter was highly related to shear (r = .73, P < .01). Hostetler t l. (1970) obtained similar results when carcasses were suspended from the obturator foramen. In addition to the contribution of connective tissue, carcass position appears to account for much of the remaining proportion of the variation found in tenderness. 30 State of Rigor. The phenomenon of rigor mortis is complete when the concentration of ATP has been depleted and glycogen is converted to lactate. Once rigor mortis has set in, muscles become relatively inextensible (Newbold and Harris, 1972) due to the formation of the actomyosin complex and concomitant shortening of muscle fibers. Marsh and Leet (1966 a, b) and Davey, Kuttel and Gilbert (1967) have shown that shortening to 20 percent of the excised (prerigor) length produced relatively small changes in tenderness, whereas further shortening from 20 to 40 percent produced a several fold increase in shear value. Herring g£_§l, (1967a)reported that tenderness of contracted muscles did not reach acceptable levels even after 10 days of aging, but Buck, Stanley and Comssiong (1970) re- ported an increased tenderness among stretched rabbit muscles. Aging. Although meat becomes.tougher until rigor mortis is completed, an aging period at temperatures slightly above freezing results in.subse- quent increases in tenderness. Davey and Dickson (1970) reported that during the aging period the external loading required to stretch bovine sternomandibularis muscle to its fullest extent declines by S to 10 fold. They indicated that the loss of tensile strength was due to a weakening of the myofibrillar structures at the junction of the I filaments and the Z discs of the sarcomeres. Goll _£.§l' (1972) suggested that resolution of rigor was due to l) a modification of the actin-myosin interaction which results in changes in the nucleoside tri-phosphatase activities of actomyosin, changes in ig_yi££g contractile properties of actomyosin, lengthening of the rigor shortened sarcomeres and changes in the dissocia- bility of the actin-myosin complex; and 2) the loss of Z-disc integrity 31 resulting in fragmentation of myofibrils and corresponding decreases in tensile strength of the fibers. Connective Tissue. Although the role of connective tissue in ten- derness has been relegated to that of "background toughness", ultrastruc- tural changes in connective tissue during postmortem aging have been suggested to affect tenderness. Goll _Eil- (1970) concluded that post- mortem changes in connective tissue were probably due to changes in the number or strength of the cross bridges between connective tissue proteins They suggested that increases in collagen solubility were possibly due to rupture or weakening of the cross linkages between collagen molecules. On the other hand, Bouton and Harris (1972) could not mechanically measure changes in connective tissue during aging and concluded that changes in connective tissue were unlikely to contribute to the increase in tender- ness achieved during aging. Protein Solubility. The solubility of meat proteins has been impli- cated as a factor contributing to meat tenderness. Goll _£ _l. (1964 a) reported a decrease in connective tissue solubility with increasing age from 40 days to 10 years, 5 months among cattle. This decrease in solu- bility tended to parallel the decrease in tenderness attributed to age of the animal. Herring, Cassens and Briskey(l967b) and Kruggel and Field (1971) found greater collagen solubility in stretched muscle than in muscle allowed to contract. The stretched muscle was also more tender. Hegarty, Bratzler and Pearson (1963) found myofibrillar protein solubility to be positively correlated (P < .01) to tenderness. Davey and Gilbert 32 (1968) reported that approximately 52 percent of the myofibrillar proteins were extractable from unaged meat compared to 78 percent from aged meat. The aged meat was also more tender. In contrast, Dikeman and Tuma (1971) reported a negative relationship between protein solubility and tender- ness and carcass maturity. Cold and Thaw Shortening. Cold shortening occurs when prerigor muscle is exposed to temperatures approximately 0 to 15 C. The muscle fibers severely contract resulting in meat toughness. Locker and Hagyard (1963) reported cold shortening in beef to be minimal at about 15 to 20 C and it became progressively greater as prerigor temperatures deviated in either direction from 15 to 20 C. Thaw rigor occurs when muscles are frozen in a prerigor state and are subsequently thawed over a short period of time. Upon thawing the muscles contract and become much tougher than muscles frozen after the completion of rigor mortis or after partial resolution of rigor (Marsh, Woodhams and Leet, 1968). The latter authors concluded that shortening and thaw rigor are capable of producing toughness Marbling. The U.S.D.A. quality grading system includes a factor in its grade determination. Marbling has long been be associated with tenderness, but its relative contribution ness is questionable. Some of the early workers (Hostetler, both cold in meat . marbling as believed to to tender- Foster and Hankins, 1936 and Ramsbottom, Strandine and Koonz, 1945) found no rela- tionship between marbling and tenderness. Cover, Butler and Car twr igh t (1956) and Alsmeyer t l. (1959) indicated that marbling had only a 33 slight association with tenderness and Blumer (1963) reported that l to 36 percent of the variation in tenderness was attributable to marbling. Covington ._£._l. (19%)) reported that moderately marbled steaks were significantly more tender than steaks with small amounts of marbling. However, the data showing little or no relationship between marbling and tenderness predominate in the literature. Walter _g _l. (1965) reported no significant effect of marbling on tenderness over a wide range of maturity groups. Reagan _g _l. (1971) reported that at 385 days of age there was no significant difference in marbling between bulls and steers, but steers were more tender. At 484 days of age steers had more marbling than bulls but tenderness was not significantly different. Goll _t‘al. (1965) and Moody, Jacobs and Kemp (1970) reported that steaks with fine textured marbling were more tender. The most recent work which conclu- sively shows a need to deemphasize marbling was reported by Parish (1972). Panel tenderness ratings were 5.2, 5.3 and 5.3 for steaks with slight, modest and moderately abundant marbling. Assessing Tenderness The Warner-Bratzler shear is one of the most widely used objective methods of evaluating meat tenderness (Banks, 1971). It was first devel- oped by Warner in 1928 and modified and improved by Bratzler in 1932. Correlations between Warner-Bratzler shear force and panel sensory scores usually range between 0.60 and 0.85 (Banks, 1971). Bratzler and Smith (1963) and Banks (1971) reported that results from shear and sensory panels 34 were highly related when measuring tenderness of cooked meat. After re- viewing many methods of objective measures of tenderness, Pearson (1963) concluded that the Warner-Bratzler shear affords one of the best relation- ships to sensory methods of measuring meat tenderness. Hormones According to the definition of Frieden and Lipner (1971), hormones are systemic-acting substances produced by specialized cells and released into the circulation to exert relatively specific effects either on all body cells or upon certain cells in specific organs. In adult animals, hormones are responsible for the integrated activity of organ systems and subsystems. They alter cellular functions in response to variation in the external environment, they induce sustained performance by cells and they change the level of activity of tissues and organs to maintain constancy of composition within the internal environment. Hormones maintain meta- bolic rates to meet the needs of the organism and are responsible for control of animal growth and differentiation. Insulin is itself anabolic and is required for the action of other growth promoting hormones. Biological phenomena stimulated by insulin include transport of glucose, certain ions and amino acids, glycogen formation, glucose conversion to triglycerides, nucleic acid and protein synthesis (Krahl, 1972) and it strongly inhibits lipolysis. Growth hormone (GH) mobilizes nonesterified fatty acids from fat depots, increases blood glucose, inhibits muscle tissue utilization of glucose, increases protein 35 synthesis and decreases the sensitivity of tissues to insulin (Frieden and Lipner, 1971). Robinowitz and Zierler (1963) suggested that growth hormone and insulin act sequentially between periods of food intake to 'maintain.an.adequate supply of energy to tissues or to store excess energy in storage depots. Robinowitz and Zierler (1963) and Weil (1965) suggested that the major emphasis in the synergistic stimulation of protein synthesis by insulin and GH changes from insulin to GH as time after food intake increases. Fat Metabolism (Insulin). Insulin is antilipolytic or inhibits fatty acid release from adipose tissues (Fain and Rosenberg, 1972). When insulin is absent, fatty acids are released from adipose tissues and marked ketosis is often seen in animals. However, insulin sufficient to inhibit fatty acid release and ketosis is much less than that required to affect blood glucose (Fain and Rosenberg, 1972). Most work relating the effect of insulin on fat cells has been through the capacity of insulin to stimulate the metabolism of glucose (Crofford 2;.al., 1972). Crofford and Renold (1965 a, b) noted that insulin stimulated glucose metabolism by accelerat- ing the carrier mediated transport of glucose into the cell. However, the antilipolytic action is not dependent on insulin's glucose transport action even though glucose metabolism has an antilipolytic action of its own. ln_yi££g.studies with isolated fat cells show that lipolysis is inhibited by insulin in both the presence and absence of glucose. In the presence of growth hormone and glucocorticoids, fatty acid release is inhibited by only one-tenth the amount of insulin required to stimulate glucose meta- bolismlnrfat cells (Fain, Kovacev and Scow, 1965; Fain, Kovacev and Scow, 36 1966). In addition, Murthy and Steiner (1972) reported increased lipo- genesis in brown adipose tissue through an effect independent of any action on glucose transport or metabolism. He observed that in an ig,yi££g glucose free system, insulin reversed the inhibition of lipogenesis. The mechanism of the antilipolytic action of insulin has not been positively determined. However, Murthy and Steiner (1972) suggested that insulin may promote lipogenesis by lowering adipocyte cyclic AMP levels. They based their hypothesis on work showing a 50 percent inhibition of acetate incorporation into fatty acids when adenosine 3', 5' cyclic AMP was added and on evidence presented by Sutherland and Robinson (1969) who showed that insulin reduced cyclic AMP levels in fat cells. In contrast, Fain and Rosenberg (1972) incubated fat cells with insulin for fifteen minutes and 2.5 hours, respectively, but found no significant effect on adenyl cyclase activity of fat cell ghosts. In addition, when they added insulin to an incubation medium containing cyclic AMP, there was no re- duction in lipolysis. They concluded that the antilipolytic action of insulin may be unrelated to the effects of insulin on cyclic AMP accumu- lation. Fat Metabolism (Growth Hormone). I2 2332, growth hormone promotes keto- sis, decreases fat stores, promotes a transfer of fat from adipose tissue to the liver and increases plasma free fatty acids (Raben and Hollenberg, 1959). Neil (1965) suggested that growth hormone increased catabolism of trigly- cerides resulting in the production of free fatty acids.‘ Goodman (1965) studied the effect of growth hormone administration on adipose tissues lg vitro. Using hypophysectomized rats, he administered fifty micrograms of GH 37 and doubled the U - 14C glucose uptake and incorporation into fatty acids. By one hour after injection, the GH effect was reduced and by 3.5 hours opposite effects were observed. Likewise, Bassett and Wallace (1966) re- ported an "insulin-like" phase with declining glucose, ketones and free fatty acids lasting for one hour after GH injection in intact sheep which was followed by a rapid increase in plasma free fatty acids to a maximum eight hours postinjection. A similar effect was observed in hypophysectom- ized sheep with one half the GH dose given intact animals. In a similar study with rats, Goodman (1968) reported an early "insulin-like" action of GH followed by "anti-insulin-like" actions with reduced glucose utilization and increased adipose tissue lipolysis after 3 hours. Similar results have been reported in dogs by Rathgeb _£‘_l. (1970) and in sheep by Davis, Garrigus and Hinds (1970). In contrast, Wheatley, Wallace and Bassett (1966) reported a slight increase in plasma glucose but no alteration in the concentration of plasma free fatty acids or ketone bodies with 5 mg GH injected daily for four weeks. Machlin (1972) stimulated lipolysis in pigs (13,3132) and in rat adipose tissues (ig_yi££2) with a commercially prepared GH. However, when the GH was further purified, tibia activity more than doubled but ig‘yiggg lipolytic activity was no longer detected. He suggested that lipolytic activity is not an intrinsic part of the porcine growth hormone molecule and is not necessary for tibia growth. Protein Metabolism (Insulin). Insulin enhances the transport of some amino acids into muscle cells and enhances the incorporation of amino acids into proteins (Manchester, 1972). In addition, Manchester and Krahl (1959) 38 noted that insulin enhances the incorporation of intracellular synthesized amino acids into protein and suggested that insulin's effect on protein synthesis is independent of amino acid transport into the tissues. Gold- stein and Reddy (1970) studied transport of amino acids into cells and their incorporation into protein in order to determine the step in protein synthesis in which insulin is effective. Amino acid transport into muscle is sodium dependent. When they incubated muscle in a sodium free system containing insulin and adequate amino acid pools there was no incorporation into the protein. They suggested that the incorporation of labeled amino acids is a result of insulin's effect on active amino acid transport. Krahl (1972) has suggested a mechanism of insulin action in which ions act as second messengers in the initiation of cellular protein synthesis. When~Mg++ and Ca++’were omitted from an ig_yi££g_incubation medium insulin caused no stimulation of protein synthesis. When Mg++ was added, baseline protein synthesis increased in adipose tissue cells if insulin was present. Insulin increased intracellular Mg++ and K+ through the Mg++ - activated (Na+ + K+) - ATPase enzyme system. The ATPase system plays a role in the insulin stimulated ion translocation. Based on the above information, Krahl (1972) has hypothesized that insulin is bound to the plasma membrane to initiate the Mg++ - activated (Na+ + K+) - ATPase enzymes which results in increased intracellular K+ and Mg++. These ions, which may be located Inear the inner surface of rough endoplasmic reticulum, may then act as second messengers to influence intracellular enzyme activities and protein synthesis . 39 Manchester (1972) has reviewed the effects of insulin on protein synthesis. He noted three factors affecting tissue protein synthesis: 1) total ribosomes present, 2) the proportion of ribosomes to polysomes and 3) regulation of the rate of movement of ribosomes along the messenger. Tissues having low rates of protein synthesis characteristically have a low polysome to ribosome ratio. When insulin is administered this ratio increases even when new RNA is not being synthesized, suggesting that in- sulin promotes initiation or the process of attaching ribosomes to m-RNA. Protein Metabolism (growth Hormong. Growth hormone increases the nitrogen content in the carcasses and pelts of hypophysectomized rats (Scow, 1959). All nitrogen fractions in the thigh muscle except alkali- soluble stroma were increased by daily GH injections (0.1 mg). When the dose was increased to 0.5 mg per day, the gains in collagen and stroma fractions were markedly increased. There was a smaller ratio of myosin to collagen in rats receiving the larger dose. Growth hormone affects protein synthesis by increasing the transport of amino acids into tissues (Jefferson and Korner, 1967), increasing the incorporation of amino acids into protein _i_rl 2.13.9 (Kostyo, 1964), in- creasing RNA synthesis (Garren ., Richardson and Crocco, 1967) and by ini- tiation of peptide chain elongation (Kostyo and Rillema, 1971). Frieden and Lipner (1971) noted that recent studies on GH action point to a role in the transcription and translation steps. The latter authors also state that RNA polymerase increased within 24 hours after GH treatment. In addi- tion, both transfer and m-RNA formation increased. However, Korner (1967) 40 has shown that actinomycin inhibits RNA synthesis but not protein synthesis suggesting that the effect of GH is not due to RNA synthesis. He also suggested that GH may influence some factor necessary for ribosomal func- tion and that RNA synthesis may be a secondary effect. Insulin and its Control. Insulin is produced by the B-cells of the pancreas through an RNA - directed mechanism involving the synthesis of a single chain polypeptide precursor (proinsulin) which is then converted to a two chain molecule by enzymes supposedly located in the Golgi apparatus (Turner and Bagnara, 1971). Crystallization of insulin was accomplished by Abel (1926). Sanger, Thompson and Kitai (1955) determined the complete amino acid sequence of insulin from several species and sheep insulin was synthesized in 1963 by Katsoyannis (1964). The bovine insulin molecule is composed of a total of 51 amino acids with 21 in the A chain and 30 in the B chain (Turner and Bagnara, 1971). The two chains are linked by disulfide bonds at positions 7 and 20 in the A chain and at 7 and 19 in the B chain. In addition, cysteine residues at positions 6 and 11 of the A chain are linked by a disulfide bridge. The three disulfide bonds are essential for molecular stability of the molecule. Insulin has been found in the circulation of fetal humans (Milner, Ashworth and Barson, 1972), fetal sheep (Bassett and Thornburn, 1971) and fetal calves (Grigsby and Oxender, 1972) after the first trimester of pregnancy. However, the mechanism of fetal insulin release is not well understood. Davis .¢_e_t__a_l_._, (1971) have shown an increase in fetal insulin in response to exogenous glucose and fructose but noted that glucose was 41 a more potent stimulant of fetal insulin release than fructose. Colwill _£_§l. (1970) have shown that exogenous insulin injected into fetal cir- culation increased fetal glucose utilization and suggested that insulin is released in hyperglycemic fetuses. The ratio of maternal to fetal in- sulin decreased with length of gestation in rabbits (Adam g£_§l,, 1969) and cattle (Grigsby and Oxender, 1972) suggesting increased release of insulin by the deVeloping fetal pancreas throughout gestation. Milner, Ashworth and Barson (1972) showed that plasma insulin could be increased with leucine in human fetuses greater than 200 grams while arginine was only effective in raising plasma insulin in fetuses less than 200 grams. They suggested that the development of different mechanisms for insulin release occurs during gestation. Burr _EIQL. (1971) have suggested a biphasic release of insulin from fetal rat pancreas ig_yi££2, They incubated pancreatic tissue in a glucose medium and showed an early (primary) immunoreactive insulin (IRI) release followed by a smaller late (secondary) release of IRI. When pyruvate was used in place of glucose, there was no release of IRI. Manns _£__l. (1967) induced an increase in plasma insulin by infusing propionate and butyrate and demonstrated that the plasma insulin increase after infusion of these volatile fatty acids (VFA) was greater than after glucose infusion in adult sheep. This finding seems reasonable since VFA .are the most important source of energy in mature ruminants. Horino _£‘_l. (1968) also demonstrated an increase in insulin secretion in ruminants by several of the short chain fatty acids produced in the rumen but no such (effect of VFA was observed on insulin secretion in nonruminant species. 42 Trenkle (19703) studied the effects of short chain fatty acids, feeding, fasting and type of diet on plasma insulin levels. Since the proportion of propionate and butyrate increases in the rumen when readily fermentable carbohydrates are fed, he speculated that diet played a direct role on insulin secretion. After a 30 hour fast, he infused acetate, propionate, butyrate, glucose and saline into sheep. By 15 minutes postinfusion, serum insulin was greatest in sheep given propionate and butyrate with no response observed in saline infused sheep. However, the response was more prolonged in sheep infused with glucose, such that by 2 hours after infusion, insulin had fallen to fasting levels in all but the glucose infused sheep. Grigsby.g£‘gl: (1972) fasted pigs for 24 hours then fed 500 g of a 16 percent protein grower diet. Within one hour after feeding, serum in- sulin had increased 17 fold, glucose rose 50 percent but free fatty acids (FFA) and glucocorticoids were reduced 50 percent. Likewise, Trenkle (1970a) fed fasted sheep and within 4 hours the average plasma insulin rose 23 percent. However, a subsequent 72 hour fast decreased plasma insulin to 32 percent of the concentration at four hours postfeeding. The sudden increase in insulin after feeding monogastric animals has been attributed in some cases to the release of gastrointestinal hormones. According to Lernmark, Hellman and Coore (1968), considerable evidence is available to show that secretin, pancreaozymdn and cholescystokinin stimu- late insulin release. They determined the effects of exogenous gastrin on insulin release from mouse pancreatic tissue ig'yiggg. In the presence of low levels of gastrin, insulin release was inhibited but when large 43 amounts of gastrin were applied to the incubation medium, insulin was re- leased. Young (1963) has suggested that gluopgon stimulates insulin secretion. Glucagon acts by increasing blood glucose concentration which in turn pro- motes insulin release. Another hypothesis for the glucagon effect on insulin is that the close prOximity of the a-cells to B-cells in the panr creas may have a physiological influence on insulin secretion (Lernmark, Hellman and Coore, 1969). They have also reviewed evidence of gastrin secretion by pancreatic a-cells and suggested that the gastrin may influence the function of the B-cells so as to increase insulin secretion. Bassett and Wallace (1967) gave adult sheep 75 mg of cortisol daily for 14 days and observed elevations in plasma glucose and insulin. However, when they increased the daily dose to 150 mg for another 14 days, plasma glucose and insulin were not significantly affected, although insulin tended to decrease during the second week of each period. They concluded that an intact sheep can maintain insulin secretion at a high rate for at least two weeks but that the sheep is unable to maintain high insulin secretion rates for prolonged periods of time. Bassett and Wallace (1967) also observed a continued hyperglycemia even when insulin concentrations were high and they suggested that glucocorticoids are antagonistic to the action of insulin on carbohydrate metabolism. Epinephrine and norepinephrine inhibit insulin secretion, though both hormones elevate blood glucose (Turner and Bagnara, 1971). The latter authors speculated that this action may be mediated through the a—cells and B-adrenergic receptors since insulin is increased when a-receptors are 44 blocked by certain drugs or when the B-receptors are stimulated. However, Creyer, Herman and Sode (1971) could not increase insulin concentrations in baboons by blocking the a-adrenergic receptors. Bassett and Wallace (1966) rapidly infused either 8 or 10 mg of ovine GH into intact sheep and reported an "insulin-like" phase lasting up to one hour. During this time, plasma glucose, FFA and ketone concentrations declined. However, FFA increased rapidly at 8 hours while glucose and ketones increased gradually. By 24 hours plasma glucose, FFA and ketones returned to normal. Bassett and Wallace (1966) also injected 0.2 mg of ovine GH per kg of body weight per day into sheep for 4 weeks. They de- monstrated a marked increase in plasma glucose and insulin concentrations. In addition, the response was biphasic and was positively correlated with increased nitrogen retention. In contrast, Manns and Boda (1965) were unable to demonstrate an increase in plasma glucose or insulin when 1 mg per kg body weight of GH was injected into sheep even though FFA were elevated and plasma amino nitrogen decreased. Likewise, Head g; 31. (1970) reported low plasma insulin concentrations in CH treated dairy calves as well as a failure of GH to elevate plasma glucose. Growth Hormone Control. Bayliss _£‘_l. (1968) have suggested three basic factors affecting GH secretion: 1) stress, 2) decreased energy supply and 3) increased amino nitrogen pool. In addition, Kokka (1972) noted that most current evidence suggests a central nervous system compon- ent regulating GH secretion. Mfiller and Pecile (1966) fasted rats for 18 hours and found that pituitary GH concentrations were reduced. This ob- 45 servation agrees with most work involving monogastric animals which shows decrease pituitary GH content but increased plasma GH concentration during fasting. When GH was administered to fasted rats, pituitary GH, plasma glucose and FFA increased. Insulin given to fasted rats markedly reduced plasma glucose, FFA and pituitary GH. Mfiller and Pecile (1966) concluded that inadequacy of available carbohydrates and the need for sources of energy other than carbohydrates, namely non-esterified fatty acids, rather than absolute hypoglycemia, seem to be the physiological state leading to “pa—7:0 a" I: I him-IT GH secretion. They also suggested an auto feed-back mechanism based on the ability of exogenous GH to inhibit endogenous GH release. Hertelendy _£H_l. (1970) infused L-Arginine into sheep and cows which resulted in prompt and marked plasma GH increases. Plasma GH was not affected by L-Arginine in pigs. Cyclic AMP and theophylline administra- tion in sheep nearly quadrupled plasma GH concentrations (Hertelendy, 1971). When theophylline was administered alone to rat pituitaries 13 XEEEQJ pituitary cyclic AMP and GH in the medium increased (Hertelendy EE .31., 1971). Epinephrine exhibited an inhibitory tendency on theophylline and cyclic AMP stimulated GH secretion. Schally E£.£l' (1968) suggested that a hypothalamic releasing hormone which travels down the hypophyseal portal system exerted a control on GH release. This factor or hormone has been isolated and purified by Schally and Arimura (1971) and has been shown to decrease pituitary GH and increase plasma or incubation medium GH both 33 3332 and ifl_!i££g, respectively. The hypothalamic GH releasing hormone not only induces GH release from the pituitary but also initiates g2 novo GH synthesis by somatotrophs. The 46 centers for hypothalamic GH control have been found to be localized in the ventromedial and arcuate nuclei and in the median eminence in rats. Stimulation of these areas by electrical shock increased plasma GH in 80 to 90 percent of the rats studied (Frohman t 1., 1971). If lesions are electrically induced in these nuclei, GH release is inhibited. Relationship of Growth to Hormones. Baird, Nalbandov and Norton (1952) measured pituitary GH in two lines (rapid and slow gaining) of pigs. They noted that rapid gaining pigs consistently had more GH per unit of anter— ior pituitary tissue than the slow gaining line. Nalbandov (1963) suggested that vigorous growth can occur only as long as the ratio of circulating GH per unit of body tissue is high enough to stimulate bone and muscle growth. Siers and Hazel (1970) bled pigs at 15, 45 and 90 kg live weight. During this time, serum GH decreased from 5.4 to 2.8 ng per milliliter. They stated that GH level declined with age and was negatively correlated with growth rate, longissimus muscle area, carcass length and percent ham and loin. They also suggested that a negative relationship may exist between hormone utilization rate and plasma GH concentration. These hypo‘ theses have been contested by Trenkle and Irwin (1970). The latter authors did not find any significant differences in plasma GH concentration between cattle 18, 198 or 393 days of age. This suggests that growth stasis due to dilution does not seem to be warranted. Siers and Swiger (1971) studied the interaction of age and weight on plasma GH in pigs. They reported negative correlations between average daily gain and weight of lean cuts per day of age. They noted that pigs 47 differing in age but not size had similar plasma GH concentrations but that pigs of increasing age and size had a lower plasma GH concentration. They concluded that size and not age was the factor responsible for the decreased plasma GH concentration° Turman and Andrews (1955) injected pigs with GH and although GH did not increase rate of gain, carcass fat content was reduced and nitrogen retention was increased leading them to conclude that true growth was stimulated. Lind t al. (1968) injected porcine GH (PGH) and measured several growth parameters. PGH increased muscle growth in the semitendin- gsgg muscle as evidenced by increased fiber diameter. PGH appeared to have a depressing effect on long bone length and circumference; however, rate of gain was not significantly affected. Likewise, Wheatley, Wallace and Bassett (1966) injected 5 mg ovine GH per day for 4 weeks into adult sheep and although no measurable change in body weight occurred, nitrogen retention and wool growth was increased. Trenkle (1970)) measured plasma insulin and GH in finishing cattle. Cattle fed stilbestrol had higher insulin GH levels and higher average daily gains than controls. Plasma insulin increased during the feeding period but presumably as a result of increased concentrates in the ration. Although this study (Trenkle,l970b) was limited to the finishing stage of growth, plasma insulin tended to be positively related to gain while GH was negatively related to gain. Curl _E 31. (1968) observed higher pituitary GH concentration in bull calves (29 to 37 kg) than feedlot steers (308 to 378 kg). Cattle with high GH per unit of body weight had carcasses with higher specific gravities 48 (less fat). They also had greater daily gains and higher percentages of body protein. Body weight was highly correlated with pituitary,adrenal and pancreatic gland weights. Macmillan and Hafs (1968) also found a close relationship between body weight and anterior pituitary weight. Both body weight and anterior pituitary (AP) weight increased linearly from birth to one year of age. The only deviation from linearity was a decrease in AP weight at 6 months. However, this was not associated with any marked changes in body growth even though it represented the onset_of puberty. They suggested an increased sensitivity of the pituitary to in- creasing androgen titers. Dev and Lasley (1969) did not find any differences in serum GH between dwarfs, dwarf gene carriers or normal cattle. They suggested a failure of the target cells and organs to respond to GH rather than insufficient GH release to be the cause of dwarfism. No significant correlation of GH with growth rate was observed among the cattle in these studies. Trenkle(l970b) observed a close relationship between plasma insulin in finishing cattle to consumption of grain. As the ratio of grain to hay increased, plasma insulin increased. This resulted in a trend for insulin to be positively related to daily gain. Acetate has been suggested to be a chemostatic regulator of ruminant feed intake. Therefore if insulin decreases plasma acetate, then its effect on daily gain may be a result of increased feed consumption. How- ever,xfluniMuller and Colenbrander (1970) injected insulin into sheep they were able to decrease blood acetate but feed intake was unaffected. 49 Macmillan and Hafs (1968) have suggested that heifers have heavier anterior pituitaries than bulls and attributed this to a possible androgen sensitivity of the anterior pituitary. Trenkle and Irwin (1970) compared steers and heifers and reported no significant differences in plasma GH or insulin at 18 or 198 days of age but at 393 days males had higher plasma insulin concentrations. This was not attributed to sex but to the higher grain ration fed to steers compared to the roughage ration received by heifers. Likewise, Grigsby and Oxender (1972) did not observe any sex differences in Holstein fetal insulin. Relationship of Carcass Quality to Hormones. Purchas _g _1. (19713) reported lower Warner-Bratzler shear values for heifers fed melengestrol acetate (MGA). Heifers fed MGA also had lower plasma GH before slaughter which was significantly and negatively related to growth but not to any measures of carcass composition. Glucocorticoids were negatively related to growth and tenderness. Although Hafs, Purchas and Pearson (1971) have suggested that insulin may have an important effect on carcass quality, there have been no reports of such a relationship to date. Relationship of Body Composition to Hormones. Data relating hormones to certain growth parameters in meat animals (i.e. body weight, average daily gain, etc.) are found in the literature but very few studies have involved the relationship of hormones to carcass composition. In addition, little work has been reported relating endogenous hormones to either growth or composition primarily due to the inadequacy of assays in determining low physiological concentrations. One of the earlier reports involving 50 meat animals was that by Turman and Andrews (1955). They injected GH at five different levels (2.25, 3, 4.5, 5 and 10 mg per 15 kg body weight per day and saline into controls) into barrows weighing 45.4 to 52.2 kg. Dif- ferences in carcass characteristics among the hormone treated pigs were small but differences between treated and nontreated pigs were great. Average backfat thickness of controls was 4.5 cm compared to 3.6 cm for GH injected pigs. Chemical composition of controls was 10.8, 39.4 and 49.3 percent protein, moisture and fat, respectively, while the correspond- ing components in CH treated pigs were 13.5, 49.1 and 36.8 percent, re- spectively. In addition, carcass length was significantly greater in CH treated animals. Lind _E.él- (1968) injected 3 and 6 mg of porcine GH (PGH) per 15 kg body weight per day or guinea pig antiporcine GH (APGH) into Duroc barrows. Pigs given PGH had larger longissimus muscle areas and less backfat than controls and anti-PGH treated pigs. There was no difference in separable fat, muscle or bone of the left ham between treatments but pigs given 3 mg of PGH per 15 kg body weight per day tended to be most muscular. The GH treated pigs had higher percentages of lean cuts than the other groups. Likewise, Machlin (1972) reported increased growth rate and muscle mass and decreased fat thickness and percent fat of the ham among GH treated pigs. Purchas gg gl.(l97lb) fed heifers MGA beginning at 2.5 months of age or at first estrus. Heifers fed MGA had reduced jugular GH levels. Heifers fed MGA from 2.5 months of age had less bone growth relative to total car- cass weight and as a result had a higher muscle to bone ratio as well as 51 lower percentages of fat. Therefore, high endogenous plasma GH was gener- ally associated with greater bone growth, lower percentages of muscle and higher percentages of fat in the round. Trenkle and Irwin (1970) studied plasma GH and insulin relationships to growth and carcass characteristics in suckling, weanling and yearling cattle. Plasma GH concentrations were 18 and 13 ng per ml in sucklings, 16.5 and 14.3 ng per ml in weanlings and 13.5 and 10.8 ng per ml in year- lings for males and females, respectively. Plasma insulin concentrations were 20.3 and 24.3 p U per ml, 21.1 n U per m1 and 45.2 and 18.3 u U per ml for male and female sucklings, weanlings and yearlings, respectively. The only significant correlation between GH and longissimus muscle area (0.514) was found in yearlings. GH was negatively related to fat thick- ness in sucklings. Insulin was not significantly related to longissimus muscle area or fat thickness at any age. Trenkle and Irwin (1970) gave three possible explanations for the low correlations between plasma GH and insulin with carcass characteristics: 1) hormones may not be limiting factors in these animals, 2) high variations between animals, and 3) plasma level and secretion rate may not be closely related. However, Trenkle (1971a) has reported a correlation of 0.97 between GH secretion and plasma GH con- centration. Of the limited data available relating plasma insulin or CH to composition in meat animals, most suggest very low relationships. Melengestrol Acetate. Melengestrol acetate (MGA) has been shown to consistently increase feedlot gain in heifers. Bloss t l. (1966) sug- gested that MGA might exert its effect on growth by allowing continued 52 endogenous estrogen secretion since MGA had no effect on spayed heifers. Purchas _£__l, @9713) observed a 10 percent increase in daily gain with MGA while the mean jugular GH was lower among treated heifers compared to controls. In addition, MGA tended to improve tenderness and percent muscle of the round. MGA increased plasma insulin concentration in feedlot hei- fers which tended to be positively related to daily gain (Trenkle, 1970b). Kalkhoff, Jacobson and Lemper (1970) have suggested that progesterone evokes an enhanced plasma insulin response to insulinogenic stimuli which may explicate the increased gain effect of MGA. Diethylstilbestrol. Diethylstilbestrol (DES) increases growth rate in steers provided adequate carbohydrate sources are available (Clegg and Cole (1954). . Hafs _p‘al. (1971) noted that in almost all cases both cattle and sheep have responded to DES with increased daily gains and increased pituitary weights. Trenk1e(1970b) observed increased daily gain, pituitary weight and elevated plasma GH in steers and increased plasma insulin and GH in heifers receiving DES. Hafs _£.§l' (1971) suggested that increased growth response to DES is probably a function of insulin secre- tion. Bidner _£‘_l. (1972) observed that DES plus methyltestosterone (MT) increased gain efficiency and pituitary weights in barrows and gilts and daily gain in barrows. The hormones also decreased carcass fat and in- creased muscling. The hormone treatment did not affect taste panel eval- uation of roasted loins. These results were observed among pigs studied on a weight constant basis. The effect of DES +'MT upon muscle and fat were not evident among pigs when studied on a constant age basis. MATERIALS AND METHODS This study was not designed to be a controlled experiment with regard vto breed, sex, age, size, ration or housing. In fact, the cattle used in this study were included in order to maximize variability between groups as well as their availability at Michigan State University. Experimental Animals Sixteen Hereford bulls, l7 Angus steers, 40 Holstein heifers, l9 Holstein steers and 13 Holstein bulls were used (table 1) in this study. All cattle were fed twice daily, at 7 am and 3 pm and were on experiment either in 1967 to 1968 or 1970 to 1971. All animals were weighed monthly and again just prior to slaughter. TABLE 1. EXPERIMENTAL ANIMALS. Breed Sex Number of animals Group number Hereford Bulls 16 l Angus Steers l7 2 Holstein Heifers 40 3 Holstein Steers l9 4 Holstein Bulls 13 5 Hereford Bulls. These bulls were selected from an experiment con- ducted at MSU in which selection of two separate lines based on tenderness 53 54 or leanness was made over a period of 12 years. They were housed commun- ally in an open-fronted shed (MSU Beef Cattle Research Center) and were fed 2.7 kg of corn silage, 3.9 kg of corn and 0.45 kg of a 64% protein supplement (85% dry matter basis) per day. These bulls were slaughtered at approximately 14 to 16 months of age. Angus Steers. These steers were compact, small framed animals which were purchased primarily for silage "cleanup” and were not fed the same ration throughout the feeding period. They were fed shelled corn and corn silage supplemented with Pro-Sil (liquid suspension of anhydrous ammonia, minerals and molasses, Ruminant Nitrogen Products Co., Adrian, Michigan). Proportions of corn and silage varied throughout the experi- ment. They were housed in an outside lot. Since ages were not known, weight or subjective estimation of market finish was used as an indication of being ready for slaughter. Holstein Heifers. These heifers were part of an experiment conducted by Purchas (1969). Beginning at 2.5 months of age, 20 heifers were fed 0.9 kg of grain per day (low) and the other 20 were fed 4.5 kg of grain per day (high). Ten heifers from each group were fed 0.45 mg of melenges- trol acetate (MGA, The Upjohn Co., Kalamazoo, Michigan) per animal per day (table 2). All heifers were fed corn silage and alfalfa hay §g_libitum. They were kept in loose housing dry-lot facilities (MSU dairy department) and penned communally according to nutritional treatments. The heifers were slaughtered at breeding size (120 cm withers height). ‘1. 55 TABLE 2. GROUPING 0F HOLSTEIN HEIFERS ACCORDING TO TREATMENT. Group Number of Level of MGA Slaughter number animals nutrition administration criteria 8 10 4.5 kg 0.45 mg/day Breeding grain/day from 2.5 mo. size 9 10 0.9 kg 0.45 mg/day Breeding grain/day from 2.5 mo. size 10 10 4.5 kg None Breeding grain/day size , ll 10 0.9 kg None Breeding grain/day size Holstein Steers. These steers were included in a nutritional experi- ment involving the feeding of two different maturity levels of corn silage. They were penned communally in two lots on the basis of nutritional treat- ment (table 3). Group 12 was fed corn silage harvested at 35% dry matter (DM) and group 13 was fed corn silage harvested at 46% DM. Silage at both levels of DM was treated with 22.5 g of Pro-SiL/kilogram of 35% DM silage (Henderson t 1., 1971). These steers were slaughtered earlier than ori- ginally planned because of the depletion of the supply of corn silage. Holstein Bulls. These bulls were provided by Michigan Animal Breeders Co-Op and Select Sires, Inc. They were housed inside either individually or in groups of 3 or 4 animals. They were fed a growing ration consisting of 4.4 kg of corn, 2.2 kg of oats, 0.5 kg of SBM, 0.1 kg of trace miner- alized salt, 0.14 kg of molasses and 3.6 kg of mixed hay per day. These bulls were used for semen collection and were not slaughtered. 56 TABLE 3. GROUPING OF HEREFORD BULLS AND HOLSTEIN STEERS ACCORDING TO TREATMENT. Group Number of number Breed Sex animals Treatment 6 Hereford Bull 9 Selected for tenderness 7 Hereford Bull 7 Selected for leanness 12 Holstein Steer 10 Corn silage harvested at 35% DM + Pro-Sil 13 Holstein Steer 9 Corn silage harvested at 46% DM + Pro-Sil Serum Collection The Holstein bulls were bled by tail vein puncture using vacutainers to collect 40 ml of blood. The remaining cattle were bled by jugular vein puncture while secured in a restraining chute. Both Angus steers and Hereford bulls became excited during blood collection. All blood was collected in polyethylene centrifuge tubes, allowed to stand at room temp- erature for 2 to 3 hr., loosened from the walls of the centrifuge tubes and cooled at 4 C for 24 hours. Serum was separated by centrifugation at 10,000 rpm in a Sorval RC-ZB centrifuge (Ivan Sorval Inc., Norwolk, Connecticut), decanted into 7 dram plastic snap-cap vials and frozen at -30 C. The plasma collected from Holstein heifers was stored as described above for serum. Prior to hormone determinations, the serum or plasma was thawed overnight at 4 C and then at room temperature for one hour. Homo- geneity of each sample was assured by inverting the vials 3 times. 57 Subsequent refreezing and thawing was carried out as described above. Slaughter Procedures Hereford bulls were slaughtered at the MSU Meat Laboratory in May,' 1971. They were fasted for 24 hr. and transported about 2 miles from the Beef Cattle Research Center on the morning of slaughter. The cattle were stunned with a captive bolt pistol and exsanguinated within 3 min. of stunning. Blood for serum hormone measurement was collected immediately after the jugular vein was severed during exsanguination. Angus and Holstein steers were transported 80 miles to a commercial abattoir (Farmer Peet's Packing Co., Bay City, Michigan) one day prior to slaughter. Two cattle were stunned at one time by captive bolt pistol followed by conventional exsanguination. The Holstein steers were slaughtered in March and Angus steers in June and July of 1971. Holstein heifers were transported approximately 5 miles to a commer- cial abattoir (VanAlstine Packing Co., Okemos, Michigan), weighed, stunned with a captive bolt pistol, and bled within 3 hr. after being removed from their experimental pens at Michigan State University. Thirty-six to 48 hr. postmortem, the right wholesale rib of Angus and Holstein steer and Hereford bull carcasses were removed, identified and shipped to the MSU Meat Laboratory where they were stored at 4 C for 24 hours. The ribs were then frozen in 46 x 76 cm cryovac bags (Cryovac Co., Cedar Rapids, Iowa) and stored at -30 C for l to 3 months. The right hind -quarters of the Holstein heifer carcasses were identified and delivered to the MSU Meat Laboratory within 4 days of slaughter. 58 Measurement of Body Composition Rgufld. Physical separation analysis of the right round of Holstein heifers was determined as described by Purchas (1969). The right hind quarter was held at approximately 4 C and all dissection procedures were carried out at this temperature within 6 days post-slaughter. After re- moval of the perirenal fat from the hindquarter, the round was separated by cutting between the fourth and fifth sacral vertebrae through a point 2 cm anterior to the exposed portion of the symphysis pubis. The flank was removed by making a cut along a line and parallel to the plane of the exposed lumbar vertebrae, starting at a point located laterally from the longissimus muscle equal to its lateral axis on the exposed muscle surface. This cut was extended to meet a second cut made tangential to the ventral surface of the rectus femoris muscle. The rounds were weighed and dis- sected into fat, muscle and bone plus tendon with no attempt being made to dissect the distal 15 cm of the round which consisted mainly of tendons and bone. 9-10-11 Rib Section. Physical separation of the 9-10-11 rib section was carried out as an estimate of carcass fat, muscle and bone. The cutting procedure used was a modification of that described by Hankins and Howe (1946). Wholesale ribs were thawed at 4 C for 3 to 5 days depending on the size of the rib. If they were not completely thawed on the morning that separation was to take place, the ribs were thawed at room temperature for about 2 hours. The 9-10-11 rib section was removed by cutting paralbl and adjacent to the posterior edges of the eighth and eleventh ribs. The 59 longissimus muscle and thoracic vertebrae were cut perpendicular to the long axis of the vertebral column of the wholesale rib. The distal ends of ribs 9, 10 and 11 were removed by cutting perpendicular to the ribs on a line measured 25 cm from the dorsal processes of the vertebrae. Fat along the ventral edges of the vertebrae and medial side of the ribs as well as excessive juice and bone dust were removed from the 9-10- 11 rib sections before they were weighed. Each 9-10-11 rib section was weighed to the nearest gram and placed into plastic bags until physical separation analyses were made. If a rib section was not completely separ- ated after being started on one day, it was wrapped in a plastic bag and stored at 4 C overnight and completed the next day. All separations were carried out at 4 to 8 C. The longissimus muscle was removed and trimmed free of fat but the epimysium was left intact. It was then weighed and immediately refrozen for later tenderness evaluation. The other large muscles of the 9-10-11 rib section were removed, freed of all separable fat and weighed as quickly as possible to decrease moisture loss from dripping and evaporation. Ex- treme care was taken to separate fat from the remaining muscles of each rib section. Components were weighed every 30 min. to minimize evaporation. All bones including cartilage were weighed and recorded as bone after being completely cleaned. The separable components were weighed to the nearest gram. Longissimus Muscle Area. A compensating polar planimeter was used to measure tracings made on acetate paper of the exposed surface (12th rib) 60 of the longissimus muscle of the right hindquarter of all cattle. Fat Thickness. A single fat thickness measurement was made of the subcutaneous fat at the 12th rib after ribbing. The measurement was made perpendicular to the outer fat surface at a point 3/4 the lateral length of the longissimus muscle from the vertical process of the 12th thoracic vertebra (American Meat Science Association, 1967) on the exposed 12th rib surface of the hindquarter. Quality Measurements Tenderness. Tenderness was measured by three different methods on the Angus and Holstein steers and Hereford bulls. Tenderness measurements were made on uncooked longissimus muscles using the Armour Tenderometer (Armour and Co., Chicago, Illinois) which is a nondestructive probe-type apparatus. The needles of the tenderometer probe were inserted into the longissimus muscle along its longitudinal axis between the 12th and 13th ribs of the wholesale ribs or intact forequarters. The probe assembly contained 10 penetration needles mounted on a manifold which in turn was attached to an electronic strain gage (Banks, 1971) from which the read- ings were directly obtained. Two separate readings were made on each rib by inserting the probe into the longissimus muscle until the penetration guide touched the muscle surface (5 cm penetration). Care was taken to prevent touching bone, large connective tissue strands or heavy intermuscu- lar fat deposits. An average of the two readings was calculated and used in the subsequent statistical analysis. 61 Warner-Bratzler shear values and taste panel tenderness scores were determined on cooked steaks from the 9-10-11 rib sections of Angus and HolStein steers, 12th rib sections of Hereford bulls and steaks from the anterior end of the short loin of the Holstein heifers. Only the longiss- img§_muscle of each of these steaks was evaluated for tenderness. Steaks from the Holstein heifers were cut approximately 2.5 cm thick, wrapped in aluminum foil and roasted to an internal temperature of 63 C in an electric oven preheated to 150 C. Shear measurements were determined 24 to 36 hours later on six - 2.2 cm cores with a Warner-Bratzler shear device. Steaks 3.8 cm thick were sawed from frozen 9-10-11 rib sections of Angus and Holstein steers and thawed overnight at 4 C. Steaks from Here- ford bulls were not frozen before cooking. The steaks from Angus and Holstein steers and Hereford bulls were cooked in deep fat (lard, 138 C) to an internal temperature of 63 to 71 C. Internal temperatures were monitored with a polyprobe potentiometer. The cooked steaks used for Warner-Bratzler shear determinations were stored overnight at 4 C. Ten - 1.2 cm cores were removed and used for the shear determinations. Taste panels were conducted with untrained panelists (16 members) to evaluate tenderness, juiciness and overall acceptability. A standard 9 point hedonic scale was used. After cooking, the steaks were trimmed to remove the browned surfaces and they were then cut into approximately 1.2 cm cubes for tasting. A total of 13 different panels were conducted with four steaks being tested at each panel evaluation. 62 Hormone Determinations Radioimmunoassay for CH. Purchas (1969) developed the double anti- body radioimmunoassay for GH used in this study. Antibodies to bovine GH (NIH-GH-BlZ) were produced in guinea pigs with an initial subcutaneous injection of bovine GH and Freund's complete adjuvant followed by subse- quent injections of GH and Freund's incomplete adjuvant (appendix I.C.2). Purchas (1969) determined that a 1:3200 dilution which bound roughly 50% of the iodinated GH was most suitable. Antibodies to guinea pig gamma globulin (Pentex, Kankakee, Illinois, Fraction II) were produced in the sheep as described above for guinea pigs (appendix I.C.l). The assay (presented in detail in appendix I.E) involved the reaction of the unknown serum and GH standards with 200 nl of guinea pig anti- bovine GH (GPABGH) for 24 hr followed by the addition of 100 ul (30,000 cpm per 100 01) of 125I-GH and incubation for 24 hours. Two hundred ul of sheep anti-guinea pig-gamma globulin (SAGPGG) were then added and incubated at 4 C for 72 hours. After the incubation period, 3 ml of 0.01 M phosphate buffered saline (PBS), pH 7.0, were added and each tube cen- trifuged at 2500 x g for 30 min in a Sorval RC-3 swinging bucket centri- fuge (Ivan Sorval, Inc., Norwolk, Connecticut). The supernatant was decanted, tubes inverted and allowed to drain for 30 min before being counted for 10 min or to 10,000 counts in a Nuclear-Chicago Model 4230 autogamma crystal scintillation counter. Radioimmunoassay_for Insulin. A modification of the radioimmunoassay for prolactin reported by Koprowski and Tucker (1971) was utilized to 63 quantify insulin. The assay consisted of a double antibody system using guinea pig antibovine insulin serum (GPABI) and sheep anti-guinea pig gamma globulin (SAGPGG) to form an insoluble complex with mass great enough to be precipitated when centrifuged at 2500 x g for 30 minutes. Standards were prepared from purified bovine insulin (Eli Lilly and Co., Indianapolis, Indiana, lot 795372, 24.2 units per mg) with 100 ul of each standard containing 0.04, 0.06, 0.08, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 3.0, 4.0 or 5.0 ng of insulin (appendix I.B.6). Guinea pig anti-bovine insulin (GPABI) was purchased from Miles Lab- oratories, Inc., Kankakee, Illinois (lot No. 21). The lyophilized serum was reconstituted with 1 m1 of deionized water, diluted 1:400 in EDTA-PBS pH 7.0, (EDTA-PBS, appendix I.B.2) and frozen in 10 ml aliquots at -30 C. To determine the correct GPABI concentration the following titer check was carried out: 1) A microsyringe (Hamilton Co., Whittier, California) was used to transfer GPABI (1:400, appendix 1.3.8) to Erlenmeyer flasks where various dilutions with normal guinea pig serum (NGPS, 1:400) as diluent were pre- pared. 2) 200 ml of the various dilutions of GPABI were added to 12 x 75 mm disposable culture tubes (Scientific Products Co., Romulus, Michigan). 3) 100 ul of 125I-Insulin (approximately 18,000 cpm per 100 01: Amersham Searle Co., Arlington Heights, Illinois, specific activity 50 u ci per US) were added to all tubes. They were then shaken and incubated at 4 C for 18 hours. 64 4) 200 01 SAGPGG (appendix I.B.9) were added, the tubes shaken and incubated for 24 hr under the same conditions described above. 5) Three ml of 0.01 M PBS were added to each tube and then centri- fuged at 2500 x g for 30 minutes. 6) The supernatant was decanted and the tubes left inverted for 30 min on absorbent paper. The tubes were then wiped dry and counted in a Nuclear-Chicago Model 4230 autogamma scintillation counter. 7) The percent of labeled insulin bound was calculated for each dilu- tion of GPABI. These results are presented in table 4 and figure 1. A dilution of l:105,000 GPABI sera was used in subsequent assays for the determination of unknown amounts of insulin. This dilution provides approximately 35% binding of the labeled insulin which is adequate to pro- vide a reasonably fast counting time but low enough to keep nonspecific binding to a minimum. In addition, a range of 30 to 40% binding provided the greatest working range on the standard curve. If greater than 40% binding was used, sensitivity at the low concentrations of the curve was lost. In contrast, if less than 30% binding was used, sensitivity at higher concentrations was lost. At approximately 35% binding sensitivity of the assay ranged from .08 to 1.0 ng per tube (figure 2). Validation of Insulin Assay. Hunter (1967) recommended that all un- known plasma should be determined at different dilutions as a check for dose response parallelism. A microsyringe was used to add 50 to 500 ul bovine and ovine sera to assay tubes to check dose response. Figure 2 shows parallel dose response curves of bovine and ovine seral dilutions to 65 TABLE 4. VARIOUS DILUTIONS OF GPABI AND THE CORRESPONDING PERCENT l251- INSULIN BOUND. Percent of 125I-insulin Dilution bound 123600 82.3 126800 79.6 1:8800 81.0 l:20,800 74.8 l:40,000 60.7 l:50,000 50.3 1:60,000 48.5 1:70,000 44.0 1:80,000 40.2 1:90,000 37.1 l:100,000 34.5 1:110,000 30.7 1:120,000 29.2 l:l30,000 27.2 l:l40,000 24.6 1 150,000 24.9 66 .Edumm cflaomcfl mcfl>onlfiucm men mmcflom qu m>uso mmcommmHICOfluSHflo .H musmflm 307: 55.0 to 223.5 CON". 00—; OD“. ON; 0.". m"— IIIIIII a a 1 4 4 Av 1 ON 1 O? 1 0w . . J. 1 om 0:300 5.3518. .1 00- $0 “COOLOn— 67 .mumm mcfi>on ocm mcfi>o new use moumocmum cflfiomcfi new mm>uso mmcommmulmmoolt.m muzoflm AND. x V Eacom _n to 5.3:. o: on o._ to 3 v0.0 4 u 1 4 H O .. ON 1 ow 1 oo 332.2» £32: £23 2:3 E33 2.33 a .. Om venom 5327.8. so .. oo. Egan. 68 the bovine insulin standard curve. The similar parallel curves of bovine and ovine serum suggest validity in using the bovine system to measure relative concentrations of ovine insulin. Koprowski and Tucker (1971) suggested that close agreement between two quantities of diluted sera in estimating prolactin concentration indi- cates that a specific hormone is being measured. Therefore, all serum samples were usually assayed at 150 and 250 HI sera providing insulin concentration was such that values were on the working portion of the standard curve. In some cases, the serum had to be further diluted to be within the workable range of the standard curve. Normal bovine sera in- cluded with each assay at 150 and 250 pl had an insulin concentration of 36.8 i 1 u U per ml (1.52 ng per m1). This also provides an indication of the repeatability of the assay since the concentration given above is an average of 36 determinations over a 5 month period. Another validation step of the assay was the determination of insulin recovery. One hundred M1 of standards (0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8 and 1.0 ng per 100 ul) were added to 150 ul of normal bovine sera. Since the insulin concentration in the normal bovine sera was known to be 0.23 ng per 150 ul, the sum of the insulin standards plus bovine normal sera could be compared to the insulin concentration actually measured when the standards and normal sera were combined. Table 5 and figure 3 show the results of insulin recovery determinations. Five hundred ng of bovine GH, FSH, LH and prolactin were incubated in the presence of GPABI to determine the specificity of the antibody for bovine insulin. In all cases, the binding of these hormones did not exceed 69 TABLE 5. DETERMINATION OF PERCENT INSULIN RECOVERED. ng of insulin ng of insulin Total ng ng std added + in 150 pl = insulin insulin Difference per tube normal bovine added actually sera measured 0.1 0.23 0.33 0.35 + .02 0.2 0.23 0.43 0.45 +-.02 0.3 0.23 0.53 0.56 + .03 0.4 0.23 0.63 0.65 + .02 0.5 0.23 0.73 0.72 - .01 0.6 0.23 0.83 0.82 - .01 0.8 0.23 1.03 0.98 - .05 1.0 0.23 1.23 1.15 - .08 the binding in those tubes which had only PBS-1% BSA. The sensitivity of the bovine insulin antibody for bovine proinsulin or fragments of bovine insulin was not determined. However, Kitabchi (1970) has reported that bovine and porcine proinsulins exhibit a similar degree of immunoreactivity and indicated that proinsulin reactivity with the insulin antibody was 25 to 33% that of insulin. Bovine and porcine connecting peptides had no significant immunoreactivity. Procedure for Insulin Assay. 1) Either 250 or 350 ul of 0.05 M phosphate buffered saline - 1% bovine serum albumin, pH 7.4, (hereafter called Buffer B l, appendix I.B.S) were added to all tubes prepared for serum samples. Four hundred U1 of B l were added to the tubes for the 7O .Edumm mcfl>on mo H1 OmH 0» ounce :HHdmCM mcH>OQ msocmooxm mo >um>oomm .m musowm 884 £32. 9. 3.. 3.0 8.0 o - d W 4 d 1 0N0 . 00.0 .. 9.0 n 00.. 353»: .. mm. 5.3:. o: 71 bovine insulin standards. This was added before volume was brought to 500 p1 with serum samples (150 or 250 p1) and standards (100 pl), respect- ively, to prevent any binding of the hormone to walls of the glass culture tubes. 2) On day zero, 200 p1 of GPABI diluted 1:105,000 (appendix I.B.8) in NGPS were added, the solution was shaken with a whirli-mixer, and then incubated for 24 hr at 4 C. 3) One hundred pl of 125I-Insulin (approximately 18,000 cpm) were added on day one, shaken and incubated at 4 C for 24 hours. 4) On day two, 200 ul of SAGPGG (dilution which would optimally pre- cipitate GPABI) were added, vortexed and allowed to incubate at 4 C for 96 hours. 5) Following incubation, 3 ml of PBS were added to each tube (except total count) and all tubes were then centrifuged at 2500 x g for 30 min in a refrigerated centrifuge with a swinging bucket rotor (Sorval Model RC-3, Ivan Sorval Inc., Norwolk, Connecticut). 6) The supernatant was decanted and the tubes left inverted on absor- bent paper for 30 minutes. The tubes were wiped dry and counted for 10 min or 10,000 counts, whichever came first, in a Nuclear-Chicago Model 4230 autogamma scintillation counter. Tube number and counting time was simultaneously punched onto a paper tape (Teletype Corp., Skokie, Illinois) which was subsequently used in the calculation of unknown insulin concen- trations. 72 Calculation of Results. A standard curve was calculated on the basis of percent of labeled insulin bound. Those tubes with 500 pl of B 1 in lieu of standard insulin were arbitrarily set at 100% binding. As the concentration of unlabeled insulin increased the percent of labeled in- sulin decreased in a dose response relationship (figure 2). The average time for each standard concentration in four sets of standards was calculated and punched onto cards with their respective in- sulin concentrations. The calculated standard curve consistently accounted for greater than 99.5% of the variation in the curve. Regression coeffi- cients calculated by the C.D.C. 3600 were entered into an Olivetti com- puter (Programma 101, Olivetti Underwood, New York, New York) which corrected for dilution and automatically calculated hormone concentrations of unknown sera as counting time and tube number were entered via the punched tape editor (Beckman Model 6912 Tape Editor, Beckman Instruments, Inc., Fullerton, California). All antibody preparations, buffers and other reagents in the study are given in detail in appendix 1. Statistical Analysis Data were analyzed on the C.D.C. 3600 computer at the Michigan State University Computer Laboratory. A least squares analysis was used to determine differences between treatment means. When significant differ- ences were observed by least squares analysis, the Duncan's Multiple Range test was utilized to determine the group means differing from each other 73 (Snedecor and Cochran, 1969). Simple correlation coefficients were deter- mined as described by Snedecor and Cochran (1969). RESULTS AND DISCUSSION The means and standard error of the means for all variables and correlation coefficients between the variables are presented in tables 8 to 24. The codes for each variable and their specific units used in the presentation of the results are defined in table 6. Each group of cattle and the treatments within groups are numbered and defined in table 7. The raw data for all variables are presented in appendix '11. Growth Rates The Holstein steers were significantly (P s .05) heavier than Here- ford bulls, Angus steers and Holstein heifers one month prior to slaughter and again at one day prior to slaughter (table 8). Hereford bulls had the highest (P s .05) average daily gain over the entire feeding period (ADGT) followed by Holstein heifers and steers which were not signifi- cantly (P > .05) different. Angus steers had the lowest (P s .05) ADGT. However, when average daily gain (ADGB) was computed for the period from the first to last bleeding (average of approximately 2.5 months) all groups were different (P s .05) from each other. Holstein steers had the highest ADGB followed by Holstein heifers, Hereford bulls and finally Angus steers. The data suggest that Holstein heifers and steers were in the acceleratory portion of the growth curve during the bleeding periods since their ADGB was greater than their ADGT. On the other hand, Hereford bulls and Angus steers had apparently reached the upper inflection 74 75 TABLE 6. NUMBER, CODE AND DEFINITION OF VARIABLES. Number Code Definition 1 BR Breed 2 SEX Sex 3 RTN Ration 4 T‘L Line selection in Hereford bulls (6 = tender line; 7 = lean line) 5 AN-NO Animal number 6 C-WT Carcass weight 7 FT-TH Fat thickness over the twelfth rib (inches) 8 LMA Longissimus muscle area (square inches) 9 RD-WT Weight of the wholesale round (pounds) 10 RD-LN Weight of separable lean from the wholesale round (pounds) 11 RD-FT Weight of separable fat from the wholesale round (pounds) 12 RD-BN Weight of separable bone from the wholesale round (pounds) 13 RD-L/BN Round, lean to bone ratio 14 RD-L/FT Round, lean to fat ratio 15 RD-% LN Round, percent lean 16 RD-% FT Round, percent fat 17 RD-% BN Round, percent bone 18 ADGT Average daily gain during total feeding period (pounds/day) l9 ADGB Average daily gain during the period from first to last bleeding (pounds/day) 20 W-B Warner-Bratzler shear values (pounds/square inch) 21 AT Armour Tenderometer (pounds) 22 JUI Taste panel juiciness (9 point hedonic scale) 23 0AA Taste panel overall acceptability (9 point hedonic scale) 24 TEND Taste panel tenderness (9 point hedonic scale) 25 RB-WT Weight of the 9-10-11th rib section (pounds) 26 RB-LN Weight of separable lean from the 9-10-llth rib section (pounds) 27 RB-FT Weight of separable fat from the 9-10-llth rib section (pounds) 28 RB-BN Weight of separable bone from the 9-10-llth rib sec- tion (pounds) 29 RB-L/BN 9-10-11 rib sectionalean to bone ratio 30 RB-L/FT 9-10-11 rib section,lean to fat ratio 31 RB-% LN Rib percent, lean 32 RB-% FT Rib percent,fat 33 RB-% BN Rib percent,bone 76 TABLE 6. NUMBER, CODE AND DEFINITION OF VARIABLES (continued) Number Code Definition 34 WT-O Live weight at slaughter or final bleeding (pounds) 35 WT-l Live weight one bleeding period before slaughter (pounds) 36 WT-2 Live weight two bleeding periods before slaughter (pounds) 37 WT-3 Live weight three bleeding periods before slaughter (pounds) 38 WT-4 Live weight four bleeding periods before slaughter (pounds) 39 AGE-0 Age at slaughter or final bleeding (days) 40 AGE-l Age one bleeding period before slaughter (days) 41 AGE-2 Age two bleeding periods before slaughter (days) 42 AGE-3 Age three bleeding periods before slaughter (days) 43 AGE-4 Age four bleeding periods before slaughter (days) 44 IN-A Average serum insulin concentration of all bleeding periods (uU/ml) 45 IN-O Serum insulin concentration at slaughter or final bleeding (DU/ml) 46 IN-l Serum insulin concentration one bleeding before slaughter (pU/ml) 47 IN-2 Serum insulin concentration two bleeding before slaughter (uU/ml) 48 IN-3 Serum insulin concentration three bleedings before slaughter (uU/ml) 49 IN-4 Serum insulin concentration four bleedings before slaughter (uU/ml) 50 GH-A Average serum GH concentration for all bleedings (Hg/m1) 51 GH-O Serum GH concentration at slaughter or final bleeding (ms/ml) 52 GH-l Serum GH concentration one bleeding before slaughter (us/m1) 53 GH-2 Serum GH concentration two bleedings before slaughter (ms/m1) 54 GH-3 Serum GH concentration three bleedings before slaughter (us/m1) 55 GH-4 Serum GH concentration four bleedings before slaughter (us/m1) 77 TABLE 7. GROUP NUMBER AND DESCRIPTION. Group number Description 10 11 12 13 Hereford bulls Angus steers Holstein heifers Holstein Holstein Hereford Hereford Holstein Holstein Holstein Holstein Holstein Holstein steers bulls bulls selected for tenderness bulls selected for leanness heifers fed high nutrition plus MGA heifers fed low nutrition plus MGA heifers fed high nutrition without MGA heifers fed low nutrition without MGA steers fed corn silage harvested at 35% DM steers fed corn silage harvested at 46% DM 78 .Amo.v m0 mHucmonwome ummmwu muawuomquSm unmummmflo cuw3 momma .ocHH %om o0m.o.o.o .o manna :H meowwmu mum maomflum> comm wow mufloam nwm.o a am.a e8.0 a mH.m 08.0 a s~.~ m-.o a mm.o aka.o a as.a Ammo mega 000.0 a mH.~ oso.o a AH.N e8.0 a om.a emo.o a mm.m Away euo< so.n a oH.mm~ Amqv «-mu< mo.s a mm.wm~ Amsv m-mo< uoH.ma a mo.mmm poo.a a om.sam Aasv N-mu< nos.oa a mo.omm 0mm.“ a mm.nem na~.q a aa.kmm Aoev H-mo< soH.aa a mo.emm usm.s a No.mam nem.e a mH.mHe Ammo o-mu< H~.~H a mm.aom AmmV «-93 so.~H a Na.m~o AamV m-e3 uom.aq a oo.meoH nao.mo a so.mmo Acne «-93 ems.wm a mm.H~HH UHO.HH a Na.wmm emo.ma a oo.~am ama.ma a mo.amk neo.o~ a mN.som Ammo H-e3 ueH.Nq a mo.NoHH um¢.ma a 0H.HHHH emo.NH a wo.omw nko.nu a NH.mam nsm.aa a No.wa Aemv o-ez mow, ~¢w, ans Ame, ~40 massage mHHSD waumaom mummwum CwmumHOI mumwwwfi CkumHO$ mummum meC< mHHDQ UHOmemm USN 0000 macho mfinmwum> .mmzomu xmm az< amaze msoum<> so mmemH HmCOwuHuuac mo mmmH nuummmu <02 0: no <02 new mumwwon cwmumaom mo muwmuu nu3ouw mo muouuo upmocmum use momm2w .ucmEummuu <02 mo mmmfiuumwmu ooflufinusc mo mHm>mH 302 no swan umcuflm new mummflmn :wmumao: mo muflmuu su30uw mo muouum uumocmum com momm2m .200. v 00 sauemuauacwam umwwwo muafluomumasm ucmumwwwo £003 momma .asouw xmm one compo ham aficufi3 mafia mom coo.o .5 use m .N mmfiomu CH meowwmu mum mucmeummuu osouoo .o mfiomu ow umCHmmo mum mHomfium> comm now meadow 0H.0 a 00.~ 00.0 a am.N No.0 a 0~.N 00.0 a em.~ Ammo 000< oso.o a wo.~ omo.o a 0N.~ um0.o a co.m ooH.o a qw.~ Awfiv Hoa< om.ma H mm.¢~m 0o.om a oo.m¢m mn.¢~ a mo.mHm mm.w2 a 05.nqw Aqmv Que: <02 oz <02 Gawuwuuso 304 :ofluwuusc awe: wmummwmc owmumao: mmumwwmc :wmumHo: 0NN.0 a 00.~ o-.0 a 00.0 0N.0 a am.a 0N.0 a 50.0 2020 000< 000.0 a a0.~ 000.0 a 00.~ 00.0 a 00.N 00.0 a 0m.~ 2020 so0< -.m2 a mm.wmm wo.w2 a oo.wmm om.qm a «H.0mw ~0.m~ a ca.mne Ammo 2-93 mH.om a oo.maoH m~.mH a om.mNHH <0.~m a o~.20w ww.- a aq.mom Aqu Onez 20 New 20 Nmm smog umoomH mucosa: com mummum owmumaom mafioo oMOMmumm mooo mfiomwum> nmsouo .mmmmhm ZHMquom Dz< mammHmm zHMquom .mAADm QMOhmMmm ZHEHH3 mmDOMUmDm HZM2H .05) and Holstein steers (r = 0.34, P > .05) (tables 12, 13 and 15). Weights of the 9-10-11 rib sections did not differ significantly be- tween Hereford bulls, Angus steers or Holstein steers; however, significant differences in separable components were observed (table 10). Angus steers had less RB-LN (P s .05) and more RB-FT (P S .05) than Hereford bulls or Holstein steers while Holstein steers had more RB-LN than Angus steers (P s .05) and less RB-FT and more RB-BN than either Hereford bulls or Angus steers (P s .05). Hedrick (1968) reported lower percentages of subcutan- eous fat among dairy breeds compared to beef breeds and Branaman t 1. 82 .Amo.v m0 kHucmo000cw0m 000000 000000000050 ucmpmMMHo 5003 0:008 .mGHH mam o00.0.o 00000um> £000 000 000:00 .0 maomu :0 om50wmo mum 000.0 a 00.00 000.0 0 00.00 000.0 0 00.00 0000 20 0-00 000.0 0 00.00 000.0 a 00.00 000.0 0 00.00 0000 00 0-00 000.0 0 00.00 000.0 0 00.00 000.0 0 00.00 0000 20 0-00 000.0 a 00.0 000.0 a 00.0 000 0 0 00.0 0000 00\0-00 000.0 0 00.0 000.0 a 00.0 000.0 0 00.0 0000 20\0-00 000.0 0 00.0 000.0 a 00.0 000.0 0 00.0 0000 20-00 000.0 a 00.0 000.0 0 00.0 000.0 0 00.0 0000 00-00 000.0 0 00.0 000.0 0 00.0 000.0 0 00.0 0000 20-00 00.0 0 00.0 00.0 0 00.0 00.0 0 00.0 0000 02-00 00.0 0 00.0 0000 0200 000.0 0 00.0 000.0 0 00.0 0000 <00 000.0 0 00.0 000.0 0 00.0 0000 000 000.0 0 00.00 000.0 0 00.00 000.0 0 00.00 0000 00 000.0 a 00.00 000.0 0 00.00 000.0 a 00.00 000.0 a 00.00 0000 00000 02 00.0 a 00.00 0000 20 0-00 00.0 0 00.00 0000 00 0-00 00.0 a 00.00 0000 20 0-00 00.0 0 00.0 0000 00\0-00 00.0 a 00.0 0000 20\0-00 00.0 0 00.00 0000 20-00 00.0 0 00.0 0000 00-00 00.0 a 00.00 0000 20-00 00.0 0 00.00 000 03-00 00.0 0 00.0 00.0 0 00.0 00.0 0 00.0 00.0 0 00.00 200 <20 000.0 0 00.0 000.0 0 00.0 000.0 0 00.0 000 00-00 000.0 0 00.000 000.0 0 00.000 000.0 0 00.000 000.00 0 00.000 000 02-0 000-- 000 000 000- 0 000500 000000 :0000000 mumemL :«mumaom mummum mnwc< 0003n uuowmum: now 0000 0:000 0000000> .003020 200 Qz< ammMm mDOHm<> mo wHH oboe manmwum> n.m.mmmm9m szquom Qz< mmmmem mDQz< .mAADm Dmommmmz mo mHHQmH mm Auwscfiucoov .m.mmmm8m ZHMquom 92¢ mMmMHm mDUZ< .mqqam omommMmm mo mHH AH mqm .mqqnm .m Qmommmm: mo mHH .NH mqm mcou manm0um> AthC0ucouV .00000 00000000 00 000000 0000000 0200 2003000 002000000000 20000000000 000200 00 00000 89 000.0 u 00. w 0 0000.0 u 00. w 0 0 a m 00 u 00.- 00.0 00.- 00.0 00.0 00.0 00.0 00.- 00.0 00.0 0000 000 00.- 00.0 00.- 00.0 00.0 00.0 00.0 00.0 00.0 00.0 0000 000 00.- 00.0 00.- 00.0 00.- 00.- 00.- 00.- 00.- 00.0 0000 00 00.0 00.0 00.0 00.- 00.0 00.0 00.0 00.- 00.0 00.- 0000 ...0000 03 00.- 00.- 00.0 00.0 00.- 00.0 00.0 00.0 00.0 00.0 0000 0000 00.- 00.- 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 0000 0000 00.0 00.- 00.0 00.- 00,- 00.- 00.- 00.- 00.- 00.- 0000 20 0-00 00.- 00.0 00.- 00.0 00.0 00.0 00.0 00.0 00.0 00.0 0000 00 0-00 00.0 00.0 00.0 00.- 00.0 00.- 00.0 00.- 00.- 00.- 0000 20 0-00 00.0 00.- 00.0 00.- 00.0 00.- 00.- 00.- 00.- 00.- 0000 0000-00 00.0 00.- 00.0 00.0 00.0 00.0 00.- 00.0 00.0 0000 20\0-00 00.0 00.- 00.- 00.- 00.- 00.- 00.- 00.- 0000 20-00 00.0 00.0 00.0 00.0 00.0 00.0 00.0 0000 00-00 00.0 00.0 00.0 00.- 00.0 00.0 0000 20-00 00.0 00.0 00.0 00.0 00.0 0000 03-00 00.0 00.- 00.0 00.0 000 020 00.0 00.0 00.0 000 00-00 00.0 00.0 000 03-0 00.0 0000 0-03 0000-00 2000-00 20-00 00-00 20-00 03-00 020 00-00 03-0 0-03 00050: 000 mwou wanm0um> 0.0 0000 manm0um> .mmmmHm mDUZ< mo mHH mvoo wHLMwum> AvmncHuCOUV .m.m¢mmem mDOZ< mo mHH 00 u a 00.0 00.- 00.0 00.0 00.0 00.- 00.- 0000 00000 03 00.0 00.0 00.0 00.0 00.0 00.0 00.0 0000 0000 00.0 00.0 00.0 00.0 00.0 00.0 00.0 0000 0000 00.0 00.- 00.- 00.- 00.- 00.- 00.- A000 20 0-00 00.0 00.0 00.0 00.0 00.0 00.0 00.0 0000 00 0-00 00.- 00.- 00.0 00.- 00.- 00.- 00.0 0000 z0 0-00 00.- 00.- 00.0 00.- 00.- 00.- 00.- A000 00\0-00 00.- 00.0 00.0 00.0 00.0 00.0 00.0 0000 z0\0-00 00.0 00.0 00.0 00.0 00.0 00.0 00.0 0000 20-00 00.0 00.0 00.0 00.0 00.0 00.0 0000 00-00 00.0 00.0 00.0 00.0 00.0 0000 20-00 00.0 00.0 00.0 00.0 000 03-00 00.0 00.0 00.0 000 000 00.0 00.0 000 03-0 00.0 0000 0-03 zmuom Hm-Qm zu-Qm H3nmm .m.mMMmHm: ZHMHmAO: mo mHH 0000 0000000> 00000000000 0.0.0000000 ZHMquox mo mHH n.m.mmMMHm szHmdom mo mHH .mH mqm mwou 0000000> Av0:C0ucou0 n.0.m¢mmem szemqo: mo mHHmH 5mGO0uwuusc mo wmoavumm 00 oa 0mnu0m vow 000000: CwoumHOm mo 00000u nuaouw mo 000000 vumvcmum cam mammzo .500.v 00 0580080050050 000000 00000o000050 ucmumMW0v 2003 00008 .asouw xmw vcm Ummun 050 005003 0:00 0cm 500.0 .5 vcw m .N 085900 :0 va0wmv mum mucmEummuu asouon .0 mHQmu :0 voc5mmv mum 000000m> Loam pow 000630 000.5 0 00.50 800.0 0 00.00 00.5 0 00.00 05.5 0 00.00 5000 00800 0: 00.0 0 00.05 50.0 0 00.05 00.0 0 00.05 00.0 0 05.05 5550 20 0-00 50.0 0 50.05 00.0 0 00.05 050.0 0 00.55 850.0 0 00.05 5050 00 0-00 05.5 0 00.00 00.0 0 00.50 050.0 0 00.00 800.0 0 00.00 5050 20 5-00 50.0 0 55.0 00.0 0 50.0 050.0 0 05.0 805.0 0 00.0 5050 0050-00 000.0 0 50.0 800.0 0 00.0 00.0 0 00.0 00.0 0 50.0 5050 2050-00 055.0 0 00.55 805.0 0 50.05 00.0 0 00.05 05.0 0 00.05 5050 20-00 00.0 0 00.5 00.0 0 50.5 000.0.“ 05.0 800.0 0 50.0 5550 00-00 50.0 0 50.50 00.0 0 00.50 00.0 0 00.00 55.0 0 50.50 5050 20-00 00.0 0 55.00 50.5 0 00.00 000.5 0 00.00 800.5 0 00.50 500 02-00 50.0 0 00.0 00.0 0 00.0 00.0 0 00.0 00.0 0 50.05 500 <20 55.0 0 05.000 50.05 0 00.000 000.0 0 00.550 805.55 0 00.000 500 03-0 <02 oz <02 :0000003: 300 50000003c Lw0m 0003650 000 000008: C00005om 0000000; 0000050: mwoo m5nm0um> H 0:000 50000550080 .000000 025000002 020 0000500 25000000 .00000 00000002 szHHB mmbomumam Hzm29 comm 000 000530 .N 05000 :0 0050000 000 50000003: 00 050050.59 .0 @5900 CH 0000000 000 00.5 0 00.0 00.0 0 50.0 00.0 0 50.0 00.5 0 00.0 5000 0-00 00.0 0 05.5 00.0 0 00.0 00.0 0 00.0 50.5 0 05.0 5000 0-00 00.0 0 00.5 00.0 0 50.0 00.0 0 00.5 00.0 0 00.5 5000 0-00 00.0 5 00.0 00.0 0 50.0 00.0 0 55.0 00.0 0 50.0 5000 5-00 50.0 0 00.0 00.0 0 50.0 00.0 0 05.0 50.0 0 00.0 5500 0-00 00.0 0 00.0 00.0 0 00.0 00.0 0 05.0 00.0 0 00.0 5000 0-00 00.05 0 55.00 00.0 0 50.00 00.05 0 00.00 00.05 0 00.00 5000 0-25 00.0 0 00.00 00.0 0 00.00 50.00 0 05.00 00.05 0 00.00 5000 0-25 000.0 0 50.50 000.0 0 05.00 800.05 0 00.05 850.00 0 00.00 5500 0-25 0800.0 0 00.00 000.0 0 55.00 800.00 0 05.05 805.0 0 00.55 5000 5-25 00.0 0 55.00 00.0 0 00.00 55.05 0 00.00 00.55 0 00.00 5000 0-25 000.0 0 50.00 000.0 0 05.50 800.55 0 00.00 800 0 0 00.50 5000 0-25 000.5 0 00.00 0800.0 0 55.00 855.5 0 00.00 0855.5 0 00.00 5000 00800 03 00.0 0 55.05 00.0 0 50.05 00.0 0 00.05 00.0 0 00.05 5550 20 0-00 000.0 0 00.55 805.0 0 00.05 050.0 0 05.55 805.0 0 05.05 5050 00 0-00 0855.0 0 00.00 0800.0 0 05.00 000.0 0 00.00 800.0 0 00.00 5050 20 0-00 050.0 0 00.0 800 0 0 50.0 005.0 0 00.0 800.0 0 00.0 5050 0050-00 50.0 0 00.0 00.0 0 00.0 05.0 0 00.0 00.0 0 00.0 5050 2050-00 850.0 0 00.55 000.0 0 00.05 050.0 0 00.05 855.0 0 50.05 5050 20-00 0800.0 0 00.5 050 0 0 00.0 800.0 0 00.0 000.0 0 05.0 5550 00-00 00.0 0 00.00 50.0 0 00.00 50.5 0 00.00 55.5 0 05.00 5050 20-00 0805.5 0 00.00 050.5 0 00.00 800.5 0 00.50 000.5 0 00 00 500 03-00 00.0 0 05.0 50.0 0 05.05 50.0 0 05.0 00.0 0 50.05 500 020 005.05 0 00.000 050.05 0 00.000 000.05 0 00.000 800.05 0 00.500 500 03-0 00.0 0 50.0 005.0 0 00.5 000.0 0 00.0 805.0 0 05.0 5050 0000 050 0 0 05.0 005.0 0 00.0 000.0 0 00.5 800.0 0 00.0 5050 0000 00.55 0 00.000 05.00 0 00.000 05.00 0 00.000 50.00 0 00.000 5000 0-03 00.05 0 00 000 05 00 0 00.000 00.00 0 05.000 50.00 0 05.000 5500 0-03 05.05 0 00.050 00.50 0 00.000 00.00 0 55.050 00.00 0 00.005 5000 0-03 000.00 0 00.005 000.05 0 00.005 050.00 0 05.505 800.00 0 00.000 5000 5-03 0800.05 0 00.000 000.00 0 00.000 000.00 0 00.000 855.00 0 00.000 5000 0-03 5550 5050 000 000 0.080500 <02 0000053 <02 0005053 <0: 0053 002 0003 000 0008 c0000003c 3oq coHuHHusc cme cowuwuusc 304 COH000050 :w02 manmwum> n-ucmaumwuH .0000500 25000000 00 005000 025000020 020 0000000 .003000 00 000000 00002000 020 0200: .55 00000 99 .000000000 mOum02 :0 00000000000 000 0000000 00 m.m x 000000: 0000000: 00 :0 000000020 .5m0.V m0 000000000cm00 000000 000000000030 000000000 5003 0000s .0000 0:0 000.0.0 0000000 000 0000000> £000 000 000020 .0 05000 05 00.0 0 00.0 05000 0-00 800.0 0 00.0 000.0 0 05.00 05000 0-00 000.0 0 00.00 800.0 0 00.50 005.0 0 00.0 000.0 0 00.50 05000 0-00 005. 0 00.05 005.0 0 50.00 850.0 0 00.0 000.0 0 00.50 050.0 0 00.50 05000 5-00 050.0 0 00.05 000.0 0 00.00 800.0 0 00.0 005.5 0 50.50 000.0 0 00.55 05500 0-00 000.0 0 00.05 050.0 0 50.00 800.0 0 05.0 000.0 0 05.00 050.0 0 00.05 05000 0-00 05.0 0 00.00 5000 0.25 05.5 0 00.50 50.5 0 00.00 5000 0-25 000.0 0 00.00 800.05 0 50.00 000.0 0 00.00 050.0 0 00.00 5500 0-25 005.0 0 00.50 850.05 0 50.50 050.0 0 00.00 000.5 0 00.00 8005.0 0 00.00 5000 5-25 00.0 0 00 00 00.0 0 00.00 00.0 0 00.00 00.05 0 05.50 05.0 0 50.00 5000 0-25 005.0 0 05.00 800.0 0 50.05 000.0 0 50.00 000.0 0 05.00 005.0 0 05.00 5000 0-25 500 500 000 000 050 0 0000000 00.2.5 Gwmuwaom 0.00000 Cwmumaom 0000.00; waumaom mhwmum mswc< mHHDD 0.0.0me.005 00000 $0000 @3000 0000000> .000000 000 020 00000 0005000 00 2500025 020 0200000 003000 00000 00 000000 00002000 020 0200: .05 00000 lOO Neither serum insulin nor CH of Hereford bulls, Angus steers, Holstein heifers or Holsteins bulls changed significantly during the bleeding periods. Serum insulin of Holstein steers decreased from 94 u U/ml at 2 months prior to slaughter to 48 u U/ml on the day of slaughter; however, GH concentra- tion did not change during this same period of time. Trenkle (1970) re- ported an increase in insulin concentration with length of time in the feedlot. He attributed this observation to increased grain consumption. Since hormone concentrations showed little change throughout the bleeding period, presentation of the results and subsequent discussion will be restricted to average hormone concentrations (CH-A and IN-A). Holstein steers had significantly (P s .05) higher IN-A than Hereford bulls, Angus steers and Holstein heifers and bulls. The latter four groups did not differ significantly but Holstein bulls tended to have the lowest in- sulin concentrations (table 18). Trenk1e(1970b) noted that the concentra- tion of plasma insulin in finishing cattle appeared to be closely related to consumption of grain and concentrate in the ration. He also reported that lambs fed corn plus alfalfa hay had nearly twice as much plasma in- sulin as lambs fed only alfalfa hay. When readily fermentable carbohydrates are fed to ruminants a greater proportion of total volatile fatty acids produced in the rumen is made up of propionate and butyrate (Trenkle, 1970a). These fatty acids have been shown to significantly increase insulin concen- trations when infused into mature sheep (Trenkle, 1970a). In the present study, Holstein steers were fed a corn silage diet that had been treated with Pro-Sil (anhydrous ammonia, molasses and minerals). The high insulin values of Holstein steers may be due to the corn silage diet since corn silage is readily fermentable and has been found to produce high levels of lOl butyrate (Bergen personal communication). In addition, possible nonfer- mented or residual molasses could provide a source of readily digestible carbohydrate which might account for the increased serum insulin of H01- stein steers. There were no significant differences in GH-A between Hereford and Holstein bulls or between Angus steers and Holstein steers; however, bulls of both breeds had less GH-A (P s .05) than Angus and Holstein steers. Holstein heifers had significantly (P s .05) lower GH-A than the other breed and sex groups. Trenkle (1971 b) reported that dietary energy level had no effect on plasma GH concentration, although in one experi- ment he observed that sheep on grain diets tended to have lower plasma GH levels than those fed high roughage diets. In addition, he reported that neither feeding nor fasting for 72 hr had any influence on plasma GH, even though blood glucose was depressed and plasma FFA were elevated among fasted animals. Although no record was made of the consumption of rough- age of each breed and sex group in the present study, it is possible that the Angus and Holstein steers received higher roughage diets than the other breed and sex groups since they were fed primarily corn silage. The plasma GH values for Holstein heifers were determined by Purchas (1969). When plasma GH was assayed on these same samples for this study (1971), approximately 2.5 fold greater values were observed. The only explanation appears to be the possibility that a change in CH standards may have been responsible for the observed 2.5 fold differences since all other variables were the same as those described by Purchas (1969). In addition, pooled normal plasma concentrations in four GH assays were nearly 102 identical, essentially eliminating the possibility that the 2.5 fold difference occurred merely by chance alone. In order to compare GH values between breed and sex groups, a 2.5 fold correction should be applied to the Holstein heifers. Even after applying a 2.5 fold correct- ion, Holstein heifers still had the lowest plasma CH levels compared to Hereford bulls, Angus and Holstein steers or Holstein bulls. Siers and Swiger (1971) reported that sex did not influence serum GH levels in pigs. They noted that pigs at a constant age and size did not differ in serum GH levels but that differences in animal size were responsible for differ- ences observed in circulating GH concentrations. In contrast, Stern, Baile and Mayer (1971) have suggested that ruminants responded differently at different ages (suckling, weanling and mature) to various GH stimu- lants. For example, injections of deoxy-glucose into ruminants increased GH most among suckling calves and least in mature cattle while arginine infusion increased CH least among suckling ruminants. The GH values reported in this study were somewhat higher than those reported by Trenkle (1967; 1971 b) for sheep but are within the ranges reported for cattle (Trenkle, 1967; Dev and Lasley, 1969; Yousef t al., 1969; Stern gt al., 1971). Eaton, Klosterman and Johnson(l968a) have re- ported that bleeding chute stresses increased serum GH from 6 ng/ml to 116 ng/ml. This high level (116 ng/ml) declined rapidly to 13.5 ng/ml after 7 minutes. Additionally, they noted that GH levels determined in 24 daily samples fluctuated markedly from day to day with a standard error greater than the mean. Koprowski, Tucker and Convey (1972) reported that serum CH of dairy cows did not exhibit circadian periodicity and was much 103 more stable than prolactin values from the same cows. Eaton _£‘_1. (1968a) noted that the day to day variation as well as mean CH values decreased as age increased in Holstein cattle. Eaton g; El~ (1968 b) observed some breed, sex and age differences for serum CH in cattle bUt concluded that, in view of the effects of stress, any differences should be cautiously interpreted. He suggested that different CH levels in stressed animals may reflect either true differences in normal circulating levels or may reflect differences due to stress-response, length of stress, pituitary reserves or combinations of these and other factors. Correlation coefficients between serum insulin and CH in this study were low (table 19) and nonsignificant. Trenkle (1971 c) reported that large doses of insulin were required to create hypoglycemic conditions in sheep. He further stated that hypoglycemia p§£_§g_was not a stimulus for growth hormone secretion but rather sudden decreases in blood glucose provided the stimulus for CH secretion. The low but consistently negative correlations found between serum insulin and CH levels in this study may be a result of the insensitivity of ruminants to insulin induced hypogly- cemia. There were no significant differences in serum insulin or CH between the tender and lean lines of Hereford bulls (table 20). However, the tender line tended to have higher insulin and lower CH concentrations than the lean line of bulls. Among the Holstein steers, nutritional treatment did not affect serum IN-A but CH-A was significantly (P s .05) higher among steers receiving 46% DM corn silage compared to steers fed 35% DM corn silage. 104 TABLE 19. SIMPLE CORRELATION COEFFICIENTS BETWEEN VARIOUS HORMONE VALUESa. Variable code and numberb Variable code and numberb IN-A IN-O IN-l CH-A GH-O CH-l IN-A 1.0 IN-O 0.54 1.0 IN-l 0.83 0.34 1.0 CH-A —.03 -.11 -.07 1.0 CH-O -.05 -.12 -.07 0.79 1.0 CH-l -.03 -.10 -.09 0.90 0.63 1.0 an = 105; P s .05 = 0.192; P s .01 = 0.251. bUnits for each variable are defined in table 6. 105 The level of grain in the diet did not influence plasma IN-A or CH-A of Holstein heifers (table 20) which is in contrast to the findings of Trenkle (1970a, 1970b, 1971b) for ruminants. However, feeding MGA to Holstein heifers significantly (P S .05) increased plasma insulin. Haist (1965) suggested that adrenal and gonadal steroids increased insulin pro- ducing tissue and concomitantly increased insulin secretion. Bassett and Wallace (1967) reported that daily injections of cortisol produced hyper- glycemia in sheep and resulted in a marked increase in plasma insulin. These authors observed that among cortisol treated animals, glucose and insulin changes were exaggerated following feeding; however, insulin was not related to increases in glucose. A direct effect of cortisol on insu- lin secretion has not been reported, thus, Bassett and Wallace (1967) sug- gested that cortisol and possibly all glucocorticoids are antagonistic to the action of insulin on glucose metabolism in the sheep. It is pOSsible that other steroids may act similarily to cortisol in decreasing ‘glucose metabolism. If this in fact is true, theeflevated insulin levels observed for both progestin and estrogen treated cattle may be the result of the attempt of the pancreas to overcome the steroid antagonism to its action on glucose metabolism. Trenkle (1970b) has reported plasma insulin values of 46.8 uU/ml, 67.6 uU/ml and 107.0 uU/ml in control, MCA and stilbestrol treated finishing heifers, respectively. In this study, plasma CH was depressed by MGA but the differences were not significant. If blood glu- cose remains elevated during MGA treatment and if the hypothesis that CH is released only when blood glucose levels fall rapidly is accepted, then the observation that MCA depresses CH would be expected. However, blood .Hm>mH HmCOHquusc mo mmmavumwmu <0: oc uo <02 vow meMHo; swoumao: mo mufimuu cu3ouw mo muouum pumwcmum can mcm02m .ucmeumouu <0: mo mmmapumwou :oHuHuuoc mo mam>oa 30H no cw“; pmcuwm vow muomwm; cfioumao: mo muwwuu guacum mo muouuo ppmccmum was mammZm .Amo. v av sHHcmoHHHcmHm HouHHe xwm paw poops ham cfinuw3 mafia xcm cov.o mmfinmu cw nmcfiwop mum mucoEummuu asouun muawuomuwasm ucmumwwflv Luwz momma .asouw .n was m .N 106 .o mfinmu cw uwcflwwp mum wanmwum> some you muwcam mm.o H m~.m Ne.o H om.~ Ho.o H om.m ¢¢.o H No.m Ammv «-mo mc.H H oo.o em.o H oo.m om.H H Ho.e cm.H H mm.e Asmv m-:o Hm.o H CH.~ H~.o H H¢.H NN.o H mm.H om.o H HH.N Ammo N-mu Hm.o H mH.N em.o H nw.~ mm.o H mm.~ mq.o H mq.~ Ammv H-mo oq.o H mm.m oe.o H om.~ NH.o. H so.m nm.o H Hm.N Aamv o-mu mm.o H H¢.m om.o H mm.~ Hm.o H HH.m am.o H -.m Aomv «-mo eem.a H mm.wm omN.¢ H Hm.mm mm.HH H N¢.Hm nm.~ H eq.me Aoqv H-zH emm.m H oe.~m oom.mH H mm.mo Hm.oH H we.me mm.m H NH.~H Aqu m-zH nem.m H hm.om umm.mH H Hu.mn wN.HH H NN.mm om.mH H qc.em Akav N-zH enm.o H oN.HH oa~.oH H H~.on mm.HH H H~.mo 05.5 H -.Hm Aoqv H-2H emo.e H Ho.Nm uoo.w H Ho.am NH.~ H wo.~¢ we.“ H km.wq Amqv o-zH ea5.m H N¢.mm omo.n H mH.oo om.o H No.Hm o~.o H oo.¢e Aeqv «-zH mzozmom mHzomu Qz< ZHAszH ZDMmm mo mmommm Qm .05; r = 0.277, P s .05, respectively). However, the significant positive relationships of insulin at 393 days of age with weaning and yearling weights were attri- buted to increased insulin values which in turn were due to high levels of 113 grain in the diets of steers. In this study, no one variable can be im- plicated as a causitive factor for the positive relationship between IN-A and WT-O since nutritional treatment was not controlled. No explanation is apparent for the differences in correlations of CH-A with WT-O between the pooled groups and that of the individual breed r1 and sex groups. In all of the individual groups, CH-A was negatively i correlated with WT-O but a positive correlation was obtained when the 3 groups were pooled. Siers and Hazel (1970) and Bidner _t‘al. (1973) have ‘ reported negative relationships between serum CH and live weight in pigs while Dev and Lasley (1969) reported negative correlations between CH and weight of cattle. It appears that any particular trend for serum CH to be either negatively or positively correlated with WT-0 is dependent upon the homogeniety of the particular group involved. In this study and in the reported literature, negative relationships between CH and body weight are prevelant among the more homogenous groups in both cattle and pigs. As heterogeniety increased, the relationship became negative due to variation in both body weight and CH-A among the groups. ADGT was computed only for Hereford bulls, Angus steers, Holstein heifers and Holstein steers, while ADGB included the Holstein bulls in addition to the other four breed and sex groups. Insulin was positively correlated with ADGT (r = 0.26, P S .05) and ADGB (r = 0.37, P s .01) among the pooled groups of cattle. In addition, these relationships were positive, although nonsignificant, for the individual breed and sex groups. Trenkle (1970b) reported elevated insulin levels and increased daily gain in feedlot heifers fed MGA or stilbestrol when compared to control heifers. 114 In both steers and heifers,insulin was positively related (nonsignifi- cantly) to feedlot gain (Trenkle, 1970b). Hafs _g‘al. (1971) suggested that body growth may be influenced by estrogens through the action of estrogen on the pancreas since both lambs and cattle had been reported to respond to DES with increased gain and plasma insulin. They concluded that increased growth in response to DES was probably a function of insulin secretion. In contrast, Trenkle and Irwin (1970) reported non- significant negative correlations between plasma insulin and feedlot gain in cattle. ADGT (table 24) was significantly related to CH-A (r = -.32, P S .05) but the relationship of CH-A with ADGB was nonsignificant (r = -.15, P s .05). Although Trenkle and Irwin (1970) reported a positive rela- tionship between feedlot gain and plasma CH concentration in cattle, negative relationships have been reported by Trenkle (1970b), in cattle and by Siers and Hazel (1970), Siers and Swiger (1971) and Bidner _£__l. (1973) in pigs. Purchas, Macmillan and Hafs (1970) reported a positive relationship for plasma GH concentration with "specific growth rate” but when total CH content of the plasma was computed and correlated with specific growth rate the relationship was negative and highly significant. In addition, they reported a low relationship between plasma and pituitary CH concentrations. However, it should not be concluded from these ob- servations that the negative relationship of serum CH with measures of growth implies that endogenous CH is antagonistic to body growth. Indeed exogenous CH has been shown many times to increase nitrogen retention and long bone growth as well as improve feed efficiency and daily gain of pigs, cattle and sheep. If CH was being utilized or removed from the _‘u - 9...-.-n-n—nu. fl. ‘ . , 115 circulation more rapidly in rapidly growing animals, then the negative relationship would merely be a function of CH turnover. Siers and Swiger (1971) noted that circulating CH decreased as size of pigs increased and suggested that since slower growing pigs generally are smaller at any particular age the negative relationship between serum CH and growth rate is not unexpected. Trenkle and Irwin (1970) found that the plasma CH concentrations of yearling cattle were within the normal range of values found in young cattle. They suggested that a more plausible explanation for the low correlation between plasma CH and growth rate might be that with maturity, target tissues become less responsive to low physiological levels of these hormones in biological fluids. The possibility also exists that CH pg£_§g may not be directly responsible for increasing growth but may influence secondary hormones which may be potent stimulators of body growth. In a review, Tanner (1972) suggested that somatomedin, a peptide of molecular weight about 4000, may be the "growth hormone stimulated" secondary hormone responsible for body growth. In addition, he noted that after exogenous CH treatment, somatomedin remained elevated for 24 hours. If somatomedin is the true'growth hormone; then it is possible that ade- quate amounts of somatomedin to promote growth are secreted by the liver when low levels of CH are present in the circulation and that CH is not the limiting substance controlling body growth rate. Hafs _£‘_l. (1971) did not find any evidence that plasma levels of CH or androgen limited growth rates of 65 bulls studied. In the present study, fat thickness was measured in carcasses of the Hereford bulls, Angus steers and Holstein steers. Insulin was negatively related to FT-TH (r = -.37, P s .01) but FT-TH was not significantly related 116 to CH-A., The negative relationship of IN-A with FT-TH is surprising in view of the fact that insulin is a lipogenic hormone and is in contrast to work reported by Trenkle and Irwin (1970). In their studies, insulin measured at 18 and 198 days of age was positively and more highly related to fat thickness than insulin measured at 393 days of age. In the same study, plasma CH was negatively related to fat thickness, although the relationships were significant only when insulin was measured at 18 days of age. Turman and Andrews (1955) and Lind _t_al. (1968) have reported that exogenous CH decreased backfat in pigs when compared to untreated controls. Siers and Hazel (1970) reported a negative correlation between backfat of pigs and plasma CH at weaning but when CH was measured at 90 kg the relationship was positive. They suggested that since the time of most rapid fat deposition was in the latter growth stages, the correlation of backfat with CH at 90 kg was more meaningful than that at weaning. Bidner _£.al. (1973) reported that data from one experiment strongly sug- gested a negative relationship between CH and fat thickness in pigs; however, they did not observe this same relationship in a second experi- ment. Neither IN-A nor CH-A were related with LMA in this study. At 393 days of age, Trenkle and Irwin (1970) reported a positive and significant relationshiphbetween CH and LMA, while insulin only tended to be related to LMA. Siers and Hazel (1970) and Bidner.ggflal. (1973) found inconsistent and low relationships between LMA and CH at various body weights of pigs. The only significant relationship of hormones with carcass quality (tenderness) was between Warner-Bratzler shear and CH-A (r = -.69, P s .01). 117 TABLE 24. SIMPLE CORRELATION COEFFICIENTS OF SOME SERUM HORMONE VALUES WITH VARIOUS GROWTH AND CARCASS TRAITS. Variable code and number3 Variable code and number8 n IN-A (44) CH-AngO) WT-O (34) 105b 0.26 0.25 ADGT (18) 92C 0.26 -.32 ADGB (19) 105b 0.37 -.15 C-WT (6) 92C 0.38 0.55 FT-TH (7) 52d -.37 0.01 LMA (8) 92C 0.04 0.01 WB Shear (20) 92C -.01 -.69 0AA (23) 36e -.26 0.05 RB-WT (25) 52d 0.03 -.09 RB-LN (26) 52d 0.28 -.02 RB-FT (27) 52d -.24 -.13 RB-BN (28) 52d 0.31 0.29 RB-L/BN (29) 52d -.08 -.40 RB-L/FT (30) szd 0.30 0.16 RB-Z LN (31) 52d 0.27 0.01 RB-Z PT (32) 52d -.30 -.11 RB-% EN (33) 52d 0.31 0.29 3Units for each variable are defined in table 6. bGroups included = l, 2, 3, 4 and 5 (See table 7 for group identification); P s .05 = 0.192; P s .01 = 0.251. CCroups included = 1, 2, 3 and 4; P s .05 = 0.205; P s .01 = 0.267. dCroups included = 1, 2 and 4; P s .05 = 0.273; P s .01 = 0.354. eGroups included 2 and 4; P S .05 = 0.320; P S .01 = 0.412. 118 Insulin tended to be negatively related to overall acceptability, but was not related to W-B shear. To my knowledge, relationships of endogenous insulin with carcass quality characteristics have not been previously re- ported. Weight of the 9-10-11 rib was not related to either IN-A or CH-A (table 24). IN-A was positively related with RB-LN (r = 0.28, P s .05) and RB-BN (r = 0.31, P s .05) but tended to be negatively related with RB-FT (r = -.24, P > .05). CH-A was also related to RB-BN (r = 0.29, P s .05) but was not significantly related to RB-LN or RB-FT. To my knowledge, no other work has been reported involving the study of the relationship of insulin to composition; however, a number of workers have correlated carcass composition with serum CH. For example, Siers and Hazel (1970) reported negative relationships for percent ham and loin with plasma CH at weaning, 45 kg and at 90 kg live weight but these relationships were not significant. Additionally, Siers and Swiger (1971) reported low, but negative correlations for pounds of lean cuts per day of age with serum GH at 71, 104 and 147 days of age in pigs. They suggested that if SH utilization rate could be measured it should be positively correlated with the percent lean cuts and percent ham and loin. Since their correlations were negative, they suggested that animals which utilized CH at the fastest rate had the lowest circulating levels. These inferences were made lnsed on the fact that CH has a positive influence on protein deposition and a negative influence on fat deposition. Machlin (1972) reported signifi- cantly higher percentages of protein and lower percentages of fat in hams from CH treated pigs when compared to untreated controls. In contrast, 119 Bidner _£__1, (1973) reported negative correlations between serum CH and fat trim but positive relationships of serum CH with percentages of ham and loin. In a second experiment, these authors reported that the rela- tionships for the same traits were low and inconsistent. RB-L/BN was not significantly related to IN-A but was negatively related to CH-A (r = -.40, P s .01) in this study. The negative relation- ship appeared to be due to the high amount of bone in Holstein steers (which also had high serum CH) rather than to any differences of RB-LN. When the RB-L/FT was correlated with hormones, the relationships were significant (P s .05) and positive with insulin (r = 0.30) but nonsignifi- cantly positive with CH-A. These relationships are difficult to explain in view of the lipogenic role of insulin and the lipolytic effects of CH. Thus the data in this study do not conform to the expected physiological effects of CH and insulin in lipid and protein metabolism. Among the carcass components expressed as percentages, only RB-% BN was significantly (P s .05) correlated with serum CH (r = 0.29). Exogenous CH has a positive influence on long bone growth in rats. Insulin was significantly (P s .05) correlated with RB-Z BN (r = 0.31) and RB-% FT (r = -.30) while RB-% LN (r = 0.27) approached significance. The relation- ships of hormones to weight of separable components are comparable and generally of the same sign as relationships for percentages of separable components. SUMMARY Sixteen Hereford bulls, l7 Angus steers, 40 Holstein heifers, 19 Holstein steers and 13 Holstein bulls were used to study the relationship of bovine serum growth hormone (CH) and insulin to various growth and carcass criteria. The Hereford bulls were divided into two groups based on selection for either leanness or tenderness; Holstein heifers were fed on either a high or low level of nutrition with or without MGA treatment; Holstein steers were fed either 35% or 46% DM corn silage. Live weight (WT-0) was greatest (P s .05) among Holstein steers and bulls compared to Hereford bulls, Angus steers or Holstein heifers. Here- ford bulls had the highest (P s .05) ADGT (total feeding period) while Holstein steers had the highest (P s .05) ADGB (bleeding period). Holstein steers and heifers had higher ADGB than ADGT. Angus steers had signifi- cantly (P s .05) lower ADGB than the other breed and sex groups. Selection for tenderness or leanness did not affect ADC. ADGT and ADCB were signi- ficantly (P s .05) increased among Holstein steers that were fed 35% DM corn silage compared to those fed 46% DM corn silage. High levels of ' nutrition or addition of MCA to the diet increased (P s .05) daily gains among Holstein heifers. Physical separation of the 9-10-11 rib section showed that RB-LN and RB-BN were greatest for Holstein steers and RB-FT was greatest (P s .05) for Angus steers. LMA did not differ significantly but FT-TH was greatest (P s .05) among Angus steers. In general, selection for leanness or ten- derness in Hereford bulls or variation in maturity levels of corn silage 120 “2*“??21‘ 121 fed to Holstein steers did not influence carcass composition. However, Holstein heifers fed high levels of nutrition had heavier (P s .05) round weights which was primarily due to increased fat deposition. MCA depressed (P s .05) RD-BN and Warner-Bratzler shear values among Holstein heifers. Steaks from Holstein heifers were more tender (P s .05) than steaks from the other breed and sex groups but this was probably due to the cookery method. Neither serum insulin nor CH (radioimmunoassay) was significantly affected by time on feed among the breed and sex groups except for Holstein steers which had only 50% of the insulin at slaughter that was observed two months prior to slaughter. Holstein steers had significantly (P s .05) more serum insulin (IN-A) than any other breed and sex group. Bulls had less CH (CH-A) than steers and heifers had less CH-A than either steers or bulls. Hormone concentrations did not differ significantly between lean and tender line Hereford bulls but the tender line tended to have higher IN-A and lower CH-A than the lean line. Holstein steers fed 35% DM silage had significantly (P s .05) less CH-A but IN-A was not affected by silage maturity. The level of grain fed Holstein heifers had no significant in- fluence on any hormone value determined but a two-fold increase in serum insulin (P s .05) was observed among MCA treated heifers. Although the relationships were not all significant, IN-A was posi- tively related to growth criteria among individual breed and sex groups. Among Holstein heifers, IN-A was positively (P s .01) correlated with all measures of lean and negatively related to measures of bone; however, IN-A was not significantly related to fat. CH-A was positively related to 122 RD-% BN (P s .01) but not to other carcass variables in Holstein heifers. When the data of Hereford bulls, Angus steers and Holstein steers were pooled, IN-A was positively related to lean and bone criteria but nega- tively related to fat. In contrast, CH-A was negatively related to ADC and positively related to measures of bone. Breed, sex, size, nutrition and housing were different among the five breed and sex groups of cattle used in this study making it extremely difficult to imply that any particular factor was responsible for the differences observed in growth, quality characteristics or composition of these cattle. However, these data suggest that diets with a high pro- portion of grain increased fat deposition but did not affect serum hormone concentrations. In addition, corn silage with Pro-Sil as well as MCA treatment significantly increased serum insulin but had little effect on circulating CH levels. 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Swiger. 1971. Influence of live weight, age and sex on circulating growth hormone levels in swine. J. Anim. Sci. 3221229. Simone, M., F. Carroll and C. 0. Chichester. 1959. Differences in eating quality factors for beef from 18- and 30-month steers. Food Tech. 13:337. Snedecor, G. W. and W. G. Cochran. 1969. Statistical Methods. Sixth Edi- tion. The Iowa State University Press, Ames, Iowa. Stern, J. S., C. A. Baile and J. Mayer. 1971. Growth hormone, insulin and glucose in suckling, weanling and mature ruminants. J. Dairy Sci. 54:1052. Stringer, W. C., H. B. Hedrick, C. L. Cramer, R. J. Epley, A. J. Dyer, G. F. Krause and R. H. White. 1968. Effect of full-feeding for various periods and sire influence on quantitative and qualitative beef carcass characteristics. J. Anim. Sci. 27:1547. Stringer, W. C. 1970. Pork carcass quality. M P 123. Extension division. University of Missouri, Columbia, Mo. 139 Sutherland, E. W. and G. A. Robinson. 1969. The role of cyclic AMP in the control of carbohydrate metabolism. Diabetes 18:797. Swatland, H. J. and R. C. Cassens. 1972. A brief study of muscle enlarge- ment in the rat. J. Anim. Sci. 34:21. Tanner, J. M. 1972. Human growth hormone. Nature 237:433. Trenkle, A. 1967. Plasma growth hormone in sheep. J. Anim. Sci. 26:1497 (Abstr.). Trenkle, A. and R. Irvin. 1970. Correlation of plasma hormone levels with growth and carcass characteristics of cattle. Growth 34:313. Trenkle, A. 1970a. Effect of short-chain fatty acids, feeding fasting and type of diet on plasma insulin levels in sheep. J. Nutr. 100:1323. Trenkle, A. 1970b. Plasma levels of growth hormone, insulin and plasma protein bound iodine in finishing cattle. J. Anim. Sci. 31:389. Trenkle, A. 1971a. Growth hormone secretion rates in cattle. J. Anim. Sci. 32:115. Trenkle, A. 1971b. Effect of diet upon levels of plasma growth hormone in sheep. J. Anim. Sci. 32:111. Trenkle, A. 1971c. Influence of blood glucose levels on growth hormone secretion in sheep. Proc. Soc. Exp. Biol. and Med. 136:51. Tuma, H. J., R. L. Henrickson, D. F. Stephens and R. More. 1962. Influence of marbling and animal age on factors associated with beef quality. J. Anim. Sci. 21:848. Tuma, H. J., R. L. Henrickson, C. V. Odell and D. F. Stephens. 1963. Variations in the physical and chemical characteristics of the longissimus dorsi muscle from animals differing in age. J. Anim. Sci. 22:354. Turman, E. J. and F. N. Andrews. 1955. Some effects of purified anterior pituitary growth hormone on swine. J. Anim. Sci. 14:7. Turner, C. D. and J. T. Bagnara. 1971. General Endocrinology, 5th Edition. W. B. Saunders Company, Philadelphia, London and Toronto, p. 274. Waldman, R. C., W. J. Tyler and V. H. Brungardt. 1971. Changes in the carcass composition of Holstein steers associated with ration energy levels and growth. J. Anim. Sci. 32:611. Wallace, L. R. 1948. 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Breidenstein and D. S. Garrigan. 1961. Effect of preslaughter dietary stress on the carcass characteristics and palatability of pork. J. Anim. Sci. 20:871. Zinn, D. W. 1967. Quantitative and qualitative beef carcass characteris- tics as influenced by time on feed. Ph.D. Dissertation, University of Missouri. In Bovine Growth and Composition. H. B. Hedrick. Mo. Agr. Exp. Sta. Bull. 928. “mm?! 141 Zinn, D. W., C. T. Caskins, G. L. Gann and H. B. Hedrick. 1970. Beef muscle tenderness as influenced by days on feed, sex, maturity and anatomical location. J. Anim. Sci. 31:307. miiu‘l. III! 8.... APPENDIX 142 APPENDIX 1. Composition of Reagents Used In Radioimmunoassays (RIA) A. Reagents for radioiodination l. 0.5 M sodium phosphate buffer, pH 7.5 Monobasic (0.5 M) Add 69.05 g NaH2P04'H20 to distilled water. Dissolve, dilute to 1 liter. Dibasic (0.5 M) a! Add 70.98 g NazHP04 to distilled water. 2 Heat to dissolve, then dilute to 1 liter. 2 Mix monobasic and dibasic to give pH 7.5. E Dispense in 1 ml portions, store at -20'C. 1 Store the monobasic and dibasic buffers at 4‘C. 2. 0.05 M sodium phosphate buffer, pH 7.5 Solution A . NaH2P04.H2O “““““““““““““““““““““““““““““““““““““ 2.78 g Merthiolate ------------------------------------- 0.01 g Dilute to 100 ml with distilled water. Solution B NaHP04/7 H20 ----------------------------------- 26.825 g Merthiolate ------------------------------------ 0.05 g Dilute to 500 ml with distilled water. Use 16 ml Solution A, 84 ml Solution B, dilute to 400 ml with distilled water. Adjust pH to 7.5 with NaOH, if necessary. Store at 4'C. 3. Chloramine - T Upon receiving Chloramine-T dispense into small tightly sealed vials, cover with foil, and store at -20 C. Dilute 30 mg Chloramine-T to 10 ml with 0.05 M NaPO4, PH 7.5 buffer. Use within 30 minutes of preparation. Discard Chloramine-T remaining in vial. 4. Sodium metabisulfite, 2.5 ug/ul Dilute 25 mg Na28205 to 10 ml with 0.05 M NaPO4, pH 7.5 buffer. Use within 30 minutes of preparation. 5. Transfer solution Sucrose ---------------------------------------------- 1.6 g KI --------------------------------------------------- 0.1 g Dilute to 10 ml with distilled water. Dispense in 1 m1 portions, store at ~20 C. 6. Rinse solution Sucrose ---------------------------------------------- 0.3 g KI --------------------------------------------------- 0.1 g Bromphenol blue -------------------------------------- 0.001 g B. 143 Dilute to 10 ml with distilled water. Dispense in 1 m1 portions, store at -20 C. Reagents for radioimmunoassay (CH and Insulin) l. 0.01 M phosphate buffered saline, pH 7.0 (PBS) NaCl ------------------------------------------------- 143 g Monobasic phosphate ---------------------------------- 120 ml (See Appendix I. A. l) Dibasic phosphate ------------------------------------ 240 ml (See Appendix I. A. 2) Merthiolate ------------------------------------------ 1.75 g Dissolve in distilled water and transfer to a large container. Dilute to 17.5 liters with distilled water. Adjust pH to 7.0 with NaOH, if necessary, store at 4‘C. 0.05 M Disodium Ethylenediamine Tetraacetate (EDTA) - PBS, pH 7.0 Disodium EDTA ---------------------------------------- 18.612 g Add approximately 950 m1 PBS. Adjust pH to 7.0 with 5 N NaOH while stirring. Dilute to 1 liter, store at 4 C. Phosphate Buffered Saline - 1% Bovine Serum Albumin (PBS-1% BSA) BSA (Fraction V, Sterile, 35% solution serological, NBC, Cleveland, Ohio) -------------------------------- 50 ml Add 1750 m1 PBS. Mix over magnetic mixer. Store in 100 ml portions at 4'C or -20 C. Buffer A NaH2P04-2 H20 ---------------------------------------- 6.2 g Merthiolate ------------------------------------------ 0.25 g BSA ““““““““““““““““““““““““““““““““““““ 14.6 ml (See Appendix I. B. 3) Add 950 ml distilled water. Adjust pH to 7.5 with 5 N NaOH. Dilute to 1 liter, store at 4‘C. Buffer B1 NaCl ------------------------------------------------- 9.0 g Dissolve with 1 liter Buffer A1. Store at 4’C. Hormone Standards (CH and Insulin) PBS-1% BSA is used for CH and Buffer B1 is used for insulin; hereafter they will be referred to as buffers. Rinse a small screw cap vial with buffer, dry. Weigh 200-500 ug hormone on a Cahn Electrobalance and transfer to the screw cap vial. gin.— 144 Add 0.85% saline to 1 mg/ml. (Make saline slightly basic, pH 8.5, for CH and slightly acidic, pH 5.0, for insulin). Make stock hormones to 500 ng/ml with buffer. Add buffer to 100 ml volumetric flasks. Using Hamilton microliter syringes, add appropriate volumes of the stock solutions to volumetric flasks to obtain the following concentrations: CH - 0.2, 0.6, 1.0, 1.6, 2.0, 3.0, 4.0, 6.0, 8.0 and 10.0 ng/ml. Insulin - 0.4, 0.6, 0.8, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 8.0, 10.0, 12.0, 14.0, 16.0, 18.0, 20.0, 30.0, 40.0 and 50.0 ng/ml. Add buffer to final volume in each volumetric flask. Dispense each standard in quantities suitable for one assay (3 ml/tube for CH; 2 ml/tube for insulin). Freeze at -20'C and store. Thaw at room temperature or rapidly in a 38‘C water bath. 7. 1:400 Normal Guinea Pig Serum (NGPS) Obtain blood from guinea pigs that have not been used to develop antibodies. Allow blood to clot, recover serum and store the serum in convenient quantities at -20 G. Add 2.5 ml of guinea pig serum to a 1 liter volumetric flask, dilute to 1 liter with 0.05 M PBS-EDTA, pH 7.0 (See Appendix I. B. 2). Divide into 100 m1 portions and store at-20 C. 8. Guinea Pig Anti-bovine GH (GPABGH) and Guinea Pig Anti-bovine Insulin (GPABI); hereafter referred to as antibody I. Dilute the antisera to 1:400 with 0.05 M PBS-EDTA, pH 7.0. Dispense in small quantities, store at -20 C. On day of use, dilute the 1:400 antisera to the required concentration using 1:400 NGPS as diluent. 9. Anti-gamma Globulin Use sheep anti-guinea pig gamma globulin (SAGPGG) obtained from sheep injected with guinea pig gamma globulin. Dilute antisera to required concentration with 0.05 M PBS- EDTA, pH 7.0. Store at 4°C or at -20 C. C. Production of Antibodies 1. Sheep Anti Guinea Pig Gamma Globulin (SAGPGG) Dissolve 50 mg guinea pig gamma globulin (Pentex, Kankakee, Illinois, Fraction II) in 5 ml .852 sterile saline. Emulsify in 5 m1 Freund's complete adjuvant by continuous flux through an 18 gauge needle. (Considered emulsified if a droplet retains a bead form when dropped on a water surface). 145 The antigen was then injected subcutaneously in 6-8 sitason the animals side. Repeat injections every two weeks substituting Freund's in- complete for the second and subsequent injections. Antisera was collected approximately 6 weeks after the initial injection by juglar vein puncture. (Approximately 600 ml blood from a 70 kg sheep). 2. Guinea Pig Anti-bovine Growth Hormone (GPABGH) Two mg bovine GH (NIH-GH-Bl2) was dissolved in 0.5 ml saline -1 and emulsified with Freund's complete adjuvant as described above. Subsequent injections of 0.5 mg emulsified in Freund's incom- plete adjuvant were made at two week intervals (maximum of 7 injections) Blood was collected by heart puncture under either anaesthesia using a 10 ml syringe and a 1.5 inch, 18 gauge needle. Serum was recovered by centrifugation (ca 15,000 g for 30 min) after coagulation. Antisera frozen at -20 C. mum c". “a..." _. I D. Iodination Procedures A microsyringe was used to transfer 25 ul of 0.5 M phosphate buffer (pH 7.5) to a 1 m1 glass vial. 5 pg NIH-CH-B12 (l ug/ul of 0.05 M phosphate buffer, 0.85% NaCl, pH 8.5) was added. One mCi of a solution of NalzsI in NaOH (50 mCi/m1, Iso-Serve Division of Cambridge Nuclear Corp., Cambridge, Massachusetts) was added by microsyringe and contents gently shaken. After adding 75 Hg Chloramine-T (Eastman Organic Chemicals, Rochester, New York) the vial was gently shaken for 2 mins. The reaction was stopped at exactly two min. by adding 125 ng sodium metabisulfite. This reduces excess Chloramine-T and converts residual iodine to iodate. After thorough mixing, 25 Ml of 2.5% BSA in 0.01 M phosphate buffered saline, pH 7.0, was added. A 1 x 12 cm glass column packed with Bio Gel P-60, 50-100 mesh (Bio Rad Labs, Richmond, California) was equilibrated previously by passing 0.05 M sodium phosphate buffer, pH 7.5, through the column and then 2 m1 PBS-2.5% BSA were added and eluted with buffer to reduce non-specific binding of the protein hormone to the column. 100 pl of Transfer Solution (Appendix I. A. 5) were added to the iodinated CH and the contents of the vial were layered beneath the buffer on the surface of the column. 70 Ml of Rinse Solution (Appendix I. A. 6) were added to the vial, recovered, and layered beneath the buffer on the column. 146 The iodinated GH was eluted from the column under gravity with 0.05 M sodium phosphate buffer and 15 1 ml aliquots were collected in 12 x 75 mm disposable culture tubes containing 1 ml of PBS-2% BSA. The elution profile was determined by quantifying the radioactivity of 10 ul portions from each of the 15 tubes. In the elution curve the first peak repisgented the iodiggted hormone and the second represented free I The peak I-GH tube was used in the assay for GH. GH iodinated for more than 10 days was passed through a 1.2 x 20 cm Sephadex G 100 column, (Pharmacia Fine Chemicals Inc., New Market, New Jersey) to reduce the content of radiation damaged hormone. Elution procedures were the same as above. The first peak appeared to represent damaged GH as indicated by the fact that when an equal number of cpm from peaks one and two were incubated with anti-GH, more than twice as much activity from peak two was bound. Peak 3 appeared to represent free I. w—u-QH“.-—-— A ‘, .e ~ ' . . 'p i E. Radioimmunoassay for Growth Hormone On day zero PBS-1% BSA (Appendix I. B. 3) and the standards or serum to be assayed were added to 12 x 75 mm disposable culture tubes to a total volume of 500 pl. Four complete sets of NIH-GH-B 12 at concentrations of 0.1, 0.3, 0.5, 0.8, 1.0, 1.5, 2.0, 3.0, 4.0 and 5.0 ng/tube were included with each assay. The assay time was started when 200 pl of GPABGH(1:3200) were added to all tubes except the total count tubes (those with only 100 n1 1251-GH, 30,000 cpm/100 n1) and shaken gently. After a 24 hr incubation at 4°C, 100 01 of 1251-GH in PBS-1% BSA were added (about 30,000 cpm/100 ul) and incubated for 24 hr at 4 C. On day 2, 200 ul of SAGPGG at an appropriate dilution were added, tubes were shaken and incubated at 4 C for 72 hours. After incubation, 3 m1 PBS was added to each tube and centrifuged for 30 mins. at 2500 g. The tubes were decanted and left in an inverted position for 30 mins. before being wiped dry and counted. Methods of calculating results was identical to those for the insulin RIA. APPENDIX 11. 147 Raw Data A.1. Codes used to identify each animal within each variable. a Identification of variable number (appendix II. A. 2. and table 6). b l = Hereford; 2 = Angus; 3 = Holstein c l = bull; 2 = heifer; 3 = steer d l = ration fed Hereford bulls 2 = ration fed Angus steers 3 = corn silage harvested at 35% DM plus Pro-Sil 4 = corn silage harvested at 46% DM plus Pro-Sil 5 = ration fed Holstein bulls 6 = high nutrition plus MGA 7 = low nutrition plus MGA 8 = high nutrition without MGA 9 = low nutrition without MGA e 1 = selected for tenderness 2 = selected for leanness 148 APPENDIX 11. Raw Data A.2. Identification of Variable Numbera. Variable Variable Decimal Variable Variable Decimal number code places number code places 1 BRb 0 29 RB-L/BN 2 2 SEXC 0 30 RB-L/FT 2 3 RTNd 0 31 1113-7. LN 2 4 T-Le 0 32 RB-°/. FT 2 5 AN-NO 0 33 RB-% BN 2 6 C-WT 0 34 WT-O 0 7 FT-TH 2 35 WT-l O 8 LMA 2 36 WT-Z 0 9 RD-WT 2 37 WT-3 O 10 RD-LN 2 38 WT-4 0 ll RD-FT 2 39 AGE-0 0 12 RD-BN 2 40 AGE-1 0 13 RD-L/BN 2 41 AGE-2 0 l4 RD-L/FT 2 42 AGE-3 0 15 RD-% LN 2 43 AGE-4 0 16 RD-% FT 2 44 IN-A 1 17 RD-% BN 2 45 IN-O l 18 ADGT 2 46 IN-l 1 l9 ADGB 2 47 IN-2 1 20 WE Shear 2 48 IN-3 l 21 AT 2 49 IN-4 l 22 JUI 2 50 GH-A 1 23 0AA 2 51 GH-O l 24 TEND 2 52 GH-l 1 25 RB-WT 2 53 GH-2 l 26 RB-LN 2 54 GH-3 l 27 RB-FT 2 55 GH-4 1 28 RB-BN 2 ~r”:3 Ll a’b’c’d’eCodes identifying each group are given in Appendix II- A°1° 149 P‘ fl 0‘ H P‘ H P“ 0.1.— .—1 .— '— '- v-Ov-Gv—lrnv—dr—O‘F-Iv-‘r—v—v—o—Hr-o—‘o-Ifiv—r- och OCF 6mm CfiU CCU OEU OOH CQK Cfim Com Ofiu fimc Wt CH6 Cmb font. ccc mac CCh nee can 606 C06 Gab mmo mar 00h mac ccc “we EFF ewe ml 1 4 cc they Wk. .HU— W0 Lab” QF( #6“ v—b Ub— TCCIFQF “(llflum U—xl my...“ To Cdu QOQLPH~ Wm. QQH OAIU .‘NCH CC Kfiu 00W PW~ URN. C€~ NO. 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