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Twelve bulls about 12 mo of age were used to study the effects of dietary stress and realimentation on muscle glycogen depletion and repletion over time. Needle biopsy techniques were used to obtain longissimus muscle samples 11 d before fasting, at the end of fasting, and 3, 7, 10 and 14 d post-fasting. Fasting reduced (P<.05) muscle glycogen from 77 to 50 µmol glycogen-glucose/g. Depressed muscle glycogen content persisted through d 3 while animals were reestablishing normal feed consumption. A glycogen repletion rate of 3 µmol glycogen-glucose•g−1•d−1was observed from d 3 to 7.

Sixty bulls and sixty steers representing four breeds (Charolais, Simmental, Hereford and Angus) were assigned randomly, within breeds, to one of three slaughter age end points (12, 15 or 18 mo). The right side from each carcass was electrically stimulated (ES) within 1 h postmortem. The longissimus (LD), semimembranosus (SM), infraspinatus (IS) and biceps femoris (BF) muscles were removed at 7 d postmortem for sensory and shear analysis. Breed had few significant or practical effects on palatability traits. In contrast to previously reported results, bulls and steers at 12 mo of age were generally less tender than those slaughtered at 18 mo. Total cooking losses were less from bulls except in the 18 mo slaughter group. Bulls were rated more tender than steers at 15 mo but the trend was reversed at 18 mo. Electrical stimulation improved ratings for heat ring (two-toning), lean color and lean firmness. These effects were greater in the 12 mo slaughter age group and greater for steers.

The effect of grass or grain dietary regimen on meat quality was examined using 48 Hereford × Angus crossbred heifers slaughtered at .96 cm 12th rib fat thickness. Carcasses were graded after a 48-h chill and the longissimus (LH), semimembranosus (SM) and semitendinosus (ST) muscles were removed for sensory and 1- to 5-d shelf-life display evaluation. About 75% of the grass-fed heifer carcasses attained marbling scores of minimum slight or greater. Carcasses from grass-fed heifers were lighter (P<.01) in weight, coarser (P<.01) in lean texture, darker (P<.01) in lean color and had more (P<.01) yellow fat than grain-fed heifer carcasses. Steaks from grass-fed heifers were similar to steaks from grain-fed heifers in tenderness, juiciness and flavor, but were darker (P<.05) in color during retail display. All steaks were considered unacceptably dark in color after 5 d of display. Cooking losses were greater (P<.01) for the ST and least (P<.01) for the LM. In general, the LM was more tender, more juicy and possessed greater flavor intensity than the ST or SM muscles, with the SM being intermediate in response. However, it was observed that the LM was darker in color than the ST or SM during the 5-d display period.

Composition, quality and palatability characteristics of 641 steer carcasses obtained from mating Hereford and Angus cows to Hereford or Angus (HAX), Tarentaise (TX), Pinzgauer (PX), Brahman (BrX) and Sahiwal (SaX) sires were compared after adjustment of data to equal age, weight, fat thickness, fat trim percentage and marbling end points. Ranking of sire breed groups for carcass weight (kg) at a constant age was: BrX(308), TX(297), HAX (296), PX(293) and SaX(285). Rankings of sire breed groups for compositional percentages at equal carcass weights were: retail product, BrX(71.0), TX(70.2), PX(69.4), SaX(68.3)and HAX(66.9); fat trim, HAX(20.9), SaX(19.4), PX(17.4), TX(17.1) and BrX(16.0); bone, PX(13.2), BrX(13.0), TX(12.7), SaX(12.3)and HAX(12.2). The positive relationship between ranking for growth rate and for retail product percentage agrees with data from previous cycles of breed groups indicating that growthier types tend to have leaner carcasses at comparable weights. Dressing percentages at a common carcass weight were higher for BrX and SaX(63.8 and 64.0%) and lower for PX(62.0%) than for HAX(63.2%) or TX(63.2%). Breed groups reached 19% fat trim at different live weights (kilograms): HAX(438), SaX(446), TX(475), PX(481) and BrX(483). At 19% fat trim, PX had the highest marbling scores and BrX and SaX the lowest (11.3 vs 9.7). HAX had the highest marbling score at age- and weight-constant end points. BrX and SaX had the lowest marbling scores at all end points. Taste panel evaluation revealed small but statistically significant differences among breed groups in flavor, juiciness and, particularly, tenderness. HAX and PX samples were more tender and BrX and SaX samples less tender than samples from other breed groups. Although all breed group averages were acceptable or higher, 0% of HAX, 4% of PX, 7% of TX, 14% of BrX and 20% of SaX carcasses had tenderness scores less than acceptable.

Effects of sex, diet, breed, weight group and geographical location on fatty acid composition, fat color and fat firmness were examined in a factorially arranged experiment involving 32 ram and 32 wether lambs. Thirty-two Suffolksired and 32 Rambouillet-sired lambs out of Finn × white-faced (mixed breeding) ewes were fed a high or a low energy diet at the MARC or the University of Wyoming. Lambs were slaughtered in two weight groups at 63 and 76 kilograms. Ram carcasses had softer, yellower fat than wether carcasses and lambs fed the high energy diet had softer, yellower fat than lambs fed the low energy diet. Fat from rams was higher (P<.05) in branched chain fatty acids and shorter chain fatty acids with odd numbers of carbon atoms, but lower in 16:0 and 18:0 than was fat from wethers. Feeding lambs a high energy diet also increased (P<.05) levels of odd-numbered and branched chain fatty acids. The effect of sex and diet on levels of 16:0, 18:0, odd-numbered and branched chain fatty acids appeared to be additive. Weight group, breed and location had little effect on fatty acid composition, fat firmness or fat color, but some weight X location interactions were significant.

The effects of photoperiod (8 hr light: 16 hr dark [8L:16D] or 16L:8D) on performance of growing-finishing lambs were evaluated in an experiment with 24 rams and 24 wethers. All lambs were caged in groups of two in a controlled environment and fed a pelleted diet ad libitumfor the duration of the study (10 to 22 weeks of age). Performance and carcass data showed that both photoperiod and sex of lamb affected growth rate (P>.01) and feed efficiency (P>.05) but that only sex of lamb affected carcass quality (P>.05) and yield (P>.10). A sex by photoperiod interaction was not observed for any of the traits measured. Average daily gain (grams/per day) and feed efficiency (feed/gain) for lambs in the four treatment groups tested were: rams (16L:8D), 410 and 4.3; rams (8L:16D), 340 and 4.5; wethers (16L:8D), 345 and 4.6, and wethers (8L:16D), 300 and 4.8, respectively. Carcass weight, like slaughter weight, was affected by photoperiod (P>.01) and sex of lamb (P>.05); both rams and wethers exposed to long photoperiods had the heaviest carcasses. Ram carcasses were leaner, had better yield grades and were heavier than wether carcasses, yet both ram and wether carcasses graded Choice. Testosterone concentrations in serum were undetectable (>.2 ng/ml) at 22 weeks of age in wethers but were elevated (P>.01) in ram lambs exposed to short (3.4 ±1.4 ng/ml) or long (.8 ± .2 ng/ml) photoperiods. Prolactin concentrations, on the other hand, were not influenced by sex of lamb but were influenced (P>.01) by photoperiod; i.e., prolactin concentrations were high in rams (190 ± 34 ng/ml) and wethers (178 ± 28 ng/ml) exposed to long photoperiods and low in rams (43 ± 9 ng/ml) and wethers (27 ±11 ng/ml) exposed to short photoperiods. These results suggest that testosterone and prolactin may independently affect growth and performance of growing-finishing lambs.

Ram lambs, wethers and wethers implanted with Silastic capsules containing crystalline testerone were placed on test at 14.9 ± 1.1 kg and evaluated for differences in growth, performance, carcass characteristics and composition. Silastic implants that were able to maintain physiological concentrations of serum testosterone provided appropriate replacement therapy in wethers. Growth rate, efficiency of feed utilization and carcass yield of intact ram lambs and testosterone-implanted wethers were superior to the corresponding traits of wethers. Wethers had greater backfat thickness and percentage kidney and pelvic fat, and their carcasses graded higher than those of ram lambs or wethers implanted with a high dosage of testosterone. Empty body composition was significantly affected by treatment. Thus, intact rams contained more water and protein but less fat and gross energy than wethers. Testosterone-implanted wethers were intermediate in composition. Carcass water and protein were not significantly affected by treatment; however, carcass fat and gross energy were highest for wethers and lowest for intact rams. The relationship between testosterone and carcass fat and energy was dose dependent; i.e., decreased fat and energy were associated withincreased serum testosterone. In conclusion, testosterone appears to be the principal testicular hormone responsible for the superior performance and preferred carcass traits characteristic of young market rams.

Forty-four wholesale ribs from ram lambs fed one of five corn:roughage diets and slaughtered at 41 or 68 kg live weight were evaluated for differences in fatty acid composition and palatability. Total unsaturated fatty acids in subcutaneous fat were higher for lambs on diets that contained 72.57 or 79.50% corn than on diets that contained 0, 36.29 or 37.88% corn. Total polyunsaturated fatty acids followed the same trends; higher amounts were present in diets that were high in corn. Differences (P<.05) in flavor scores of ram lamb meat by diet were not related to changes in unsaturated fatty acid composition. In addition, the effect of diet on aroma, juiciness, tenderness and Warner-Bratzler shear values was not significant. Total unsaturated fatty acids were higher in fat from 68-kg lambs than from 41-kg lambs, but total polyunsaturated fatty acids decreased as weight increased. Panel scores for flavor were less desirable in rib roasts from older 68-kg rams than from younger 41-kg ram lambs, but panel scores for aroma of heated fat, juiciness and tenderness were not related (P<.05) to weight. Warner-Bratzler shear values were lower for meat from the 68-kg ram lambs than for meat from the 41-kg ram lambs. The data demonstrate that diet can influence fatty acid composition in ram lambs and that diet should be an important consideration in production of ram lambs for meat. However, the influence of diet and fatty acid composition on flavor and aroma of meat from ram lambs needs further study.

Postweaning growth data on 282 steers and carcass data on 275 steers produced by artificially inseminating (AI) yearling heifers of 12 crossbred groups (Hereford-Angus reciprocal crosses plus F1crosses produced by mating Jersey, South Devon, Simmental, Limousin and Charolais sires to Hereford and Angus cows) to Hereford, Angus, Brahman, Devon and Holstein bulls were analyzed. For postweaning growth rate, Devon-sired steers were the slowest, Holstein-sired steers were fastest and Hereford-Angus- and Brahman-sired steers were similar and intermediate. Due to their large weaning weights, Brahman-sired steers were heaviest at 452 days, followed closely by Holstein and then Hereford-Angus-AI (Hereford and Angus sires used by artificial insemination) and Devon. Steers from Jersey cross cows had the lowest average daily gain, relative growth rate and 452-day weight. Steers from the other crossbred cows group had similar postweaning growth rates, but due to weaning weight differences, Simmental, South Devon and Charolais crosses had similar 452-day weights that tended to be heavier than those of Hereford-Angus and Limousin crosses.Carcass traits were analyzed once with carcass weight as a covariate and once with slaughter age as a covariate. The analyses produced similar results. Carcasses from Holstein-sired steers had the least fat cover, smallest percentage of kidney, heart and pelvic fat (%KHP), best yield grade, highest estimated percentage retail product and lowest conformation score. Devon-sired steers had the highest %KHP fat. Brahman-sired steers had the poorest yield grade and the lowest marbling score and quality grade. Hereford and Angus-sired steers had the most fat cover, poorest yield grade and lowest estimated percentage retail product but highest conformation, marbling and quality scores. Steers from Hereford-Angus and Jersey cross cows had the most fat cover, smallest longissimusarea, highest %KHP fat, lowest yield grade and lowest percentage retail product. Steers from Jersey crosses also had the lowest conformation scores. Most other differences among cow sire breeds for carcass traits were small.

In three experiments, effects of steer genotype, dietary energy density and protein levels were evaluated in terms of growth rate, feed efficiency and carcass characteristics. Feed intake and efficiency data were grossly different among the trials, and the difference was attributable to severe environmental stresses during the trial 2 feeding period. Crude protein levels in trial 2 (11.0 vs12.9%) resulted in few meaningful differences in the traits measured suggesting the lower level was adequate to meet protein demands for the rates of gain attained. Dietary energy densities (2.66, 2.77 and 2.93 in trial 1 and 2.68 and 2.94 Meal ME/kg DM in trial 2) significantly influenced final live weight, carcass weight and percentages fat, protein and water in the carcasses. Trends were similar in trial 3 when diets containing 2.78, 2.89 or 2.95 Meal ME/kg were fed. Most of the increase in carcass weight due to increased energy density of the diet apparently resulted from increased carcass fat. No differences in amount of carcass protein or edible product were attributable to energy level. Breed group had significantly affected all carcass traits measured. Carcasses from large-type steers were heavier and contained greater amounts of protein and edible product than carcasses from small-type steers. Rate of gain favored the large-type steers, but feed efficiency was similar between the two types. Interactions between breed type and dietary treatment and between energy density and protein content of the diet were not significant. Protein and edible product produced per unit feed intake was greater in the larger, faster growing steers than in smaller, earlier maturing steers.

Four-hundred-eighty-four steers, obtained by mating sires of seven breeds and dams of two breeds, were evaluated for cannon bone size as related to performance, carcass traits and metacarpus measurements. Bone size (circumference) scores were determined on the steers just after weaning and just before slaughter, and right forecannon circumference was measured at slaughter time. Bone size, scored just after weaning, was highly related to bone size scored just before slaughter (r = .80, P<.01) and to forecannon circumference at slaughter time (r = .67, P<.01). Slaughter bone size was also highly related to slaughter forecannon circumference (r= .77, P<.01).Breed crosses differed (P<.05) in bone scores, actual forecannon circumference and carcass bone percentage. Generally, breed cross rankings for feeder calf bone scores closely paralleled rankings for slaughter bone scores and slaughter forecannon circumference. However, except for the two largest boned crosses having the highest carcass bone percentages, breed cross rankings for carcass bone percentage did not correspond with breed cross rankings for feeder or slaughter bone scores or forecannon circumference.Correlations calculated over-all breed crosses indicated that cannon bone size scores were positively correlated (P<.01) with birth weight, 200-day weaning weight, feedlot ADG and slaugther weight (range, .21 to .60). Cannon bone size was positively correlated (P<.01) with cutability and retail product percentages (range, .25 to .42), but negatively correlated with longissimus marbling score, quality grade and carcass fat percentage (range, -.18 to -.39). Cannon bone size was also positively correlated (P<.01) with carcass bone percentage (range, .15 to .31). Pooled within breed cross correlations were considerably lower than correlations calculated over-all breed crosses.Pooled over-all breed cross correlations of metacarpus circumference with cannon size scores and forecannon circumference ranged from .57 to .67. Breeds with larger metacarpus circumferences generally had larger marrow cavity areas but did not have thicker bone walls. Over-all breed crosses, marrow cavity area was highly significantly correlated with cannon size scores (range .42 to .58), while bone wall thickness was not significantly (P>.05) correlated with cannon size scores (range -.03 to .05). Ratios of total cross-sectional area to marrow cavity area (TA/MCA) indicated that breed crosses with smaller metacarpi have more bone wall area in relation to total cross-sectional area than breed crosses with larger metacarpi. The ratio of TA/MCA was inversely associated with cannon size scores, and correlations of TA/MCA with cannon size scores were negative (P<.01). Specific gravity differences among crosses were mostly nonsignificant (P>.05).When correlations between cannon bone size and metacarpus measurements were calculated on a pooled within breed cross basis, they were generally considerably lower than on an overall breed cross basis.

Carcasses from 1,121 steers (progeny of Hereford or Angus cows mated to Hereford, Angus, Charolais, Simmental, Limousin, South Devon or Jersey sires by artificial insemination) were examined to develop equations to estimate percentage of retail product. The independent variables chosen and resultant accuracy of the equations developed, reflect different kinds of measurements which could be used to predict cutability over a wide range of data collection conditions.Of 18 traits readily obtained in the cooler, adjusted fat thickness, longissimusmuscle area, estimated kidney and pelvic fat, hot carcass weight and marbling score were the most important in predicting percentage of retail product. A multiple regression equation involving these five independent variables accounted for 79.2% of the variation in percentage of retail product with a standard error of ±2.05.Partial retail cutout of the round or the rib was important (P<.01) in predicting retail product when included in equations with carcass parameters observed in the cooler.

Carcasses of 786 steers derived from crosses of Hereford or Angus cows bred to Hereford, Angus, Charolais, Limousin, Simmental, South Devon and Jersey sires were fabricated into closely trimmed, semi-boneless retail cuts to study relationships among independent variables in the U.S.D.A. yield grade equation in breed groups that differ in growth and fattening characteristics.Simple correlations indicate carcass weight was a good predictor of cutability within a breed group but a poor indicator over all breed groups. Longissimusmuscle area had the lowest predictive value of the four variables studied. It may be more useful in populations of similar weight than in those varying widely in weight. Fat thickness at the 12th rib was the most useful predictor of cutability and is about equally useful within or over all breed groups. Percentage of kidney and pelvic fat, though lower in predictive value than 12th rib fat thickness, was useful within or over breed groups. Partial regression coefficients computed within each breed group were relatively similar though there were significant differences in intercept values for the different breed groups. Use of a single prediction equation for all breed groups would rank animals well within a breed group but would on the average underestimate or overestimate animals of a breed group by .1% to over 1% relative to actual cutability.

Relationships between rate of growth, endogenous muscle enzymes and meat palatability were investigated in 48 young (13 mo) Angus bulls. After backgrounding for 4 mo, bulls were placed on a high-energy diet for 30 d, at which time they were assigned randomly to one of three feeding treatments: 1) high energy (ad libitum-fed), 2) maintenance energy (restriction-fed to maintain body weight) or 3) sub-maintenance energy (restriction-fed to lose .68 kg/d). Cattle were slaughtered after 30 or 60 d on trial. Cathepsins B and H and β-glucuronidase in the longissimus muscle were quantitated at slaughter. Serum hydroxyproline, longissimus muscle collagen, taste-panel ratings and peak load for shear were obtained. Rate of growth did not influence enzyme or palatability traits and, although differences were noted for plasma hydroxyproline, muscle collagen amount and solubility were unchanged. Overall, about one-half of the variation in serum hydroxyproline, muscle collagen, taste-panel ratings and shear-force value could be explained by collective differences in selected enzyme traits. These data indicate that a significant relationship exists between proteolytic activity of longissimus muscle and meat tenderness.

Seventy-seven heifers weighing about 200 kg were assigned randomly to 1) intact control (C), 2) ovariectomized (OVX), 3) immunized against estradiol (BSA-E), 4) BSA-E + trenbolone acetate (BSA-E+TBA), 5) TBA or 6) ovx + TBA groups. The objective of the study was to determine the effects of ovariectomy, immunoneutralization of estradiol and trenbolone acetate treatment on growth rate and carcass merit. Heifers were fed a corn-corn silage diet and were slaughtered when treatment groups attained live-animal weights of 433 kg. Observations of rate of growth, efficiency of feed conversion, characteristics of carcasses and characteristics of organoleptic properties of the cooked meat were made. Average daily gains (ADG) were similar in the control and OVX groups and tended to be less than in other treatment groups (P<.36). Although not statistically significant, the observed mean for the BSA-E+TBA treatment suggests improved ADG and TDN per unit of gain, indicating a possible immunization × TBA interaction. Data also suggested that heifers implanted with TBA had increased ADG and efficiencies of gain. Possibly, immunoneutralization of endogenous estradiol can improve ADG as compared with control and OVX groups. Treatments had no effect on color or texture of lean muscle at the 12th rib interface. The OVX + TBA group had less (P<.01) 12th rib fat cover than other groups and lower percent fat in the rib than C. The BSA-E+TBA and TBA groups also possessed larger (P<.02) longissimus muscle areas than the control group. Observations of juiciness, tenderness and flavor were similar among all treatments. Results indicate that implanting heifers with TBA and (or) immunizing against endogenous estradiol may provide opportunities to increase gains, feed conversions and lean-to-fat ratios in heifers.