Growth and metabolism in somatotropin-treated steers: III. Protein synthesis and tissue energy expenditures

Rates of in vivo protein synthesis in intercostal, sartorius and semitendinosus muscle and in the heart, liver, kidneys, rumen and jejunum were determined in 20 growing Hereford steers treated for 112 d with daily subcutaneous injections of either saline (S) or recombinantly derived bovine somatotropin (rBST; 20.6 mg/d). In vitro rates of protein synthesis and energy expenditures associated with Na+, K+ transport also were determined in external intercostal muscle, liver, kidneys and jejunum. Neither in vivo nor in vitro tissue protein fractional synthetic rates (mg/[g protein.d]), using either the plasma (P) or intracellular fluid (ICF) phenylalanine specific radioactivity for the precursor pool, were affected by rBST treatments. Energy expended on Na+, K+ transport was greater (P less than .1) in the livers of rBST-treated steers, which would increase the maintenance energy expenditures of these steers. Protein accretion rates in the liver, kidneys, stomach, hide, and head, feet and tail of rBST-treated steers were greater (P less than .05) than in S steers. Tissue amino acid profiles were not affected by rBST treatments except in the rumen, where profiles suggested that less collagen was present in rumen wall tissue protein of rBST steers. Plasma phenylalanine entry rates also were not affected by rBST treatment; muscle protein synthesis accounted for a minimum of 20% of this entry rate.     

Growth and metabolism in somatotropin-treated steers: I. Growth, serum chemistry and carcass weights

Growth, feed conversion, serum chemistry and gross slaughter characteristics were determined in 20 steers (initially 9 mo of age, 231 +/- 18 kg) receiving daily injections of either saline (S) or recombinantly derived bovine somatotropin (rBST, 20.6 mg/d) for 112 d. Live weight gains were 15% greater for steers treated with rBST than for those treated with S. Feed intake was not different between S- and rBST-treated steers; thus, feed conversion was 12% more efficient in rBST steers. Scanogram backfat measurements were not affected by treatments. Serum electrolytes, protein, glucose and most enzyme activities were similar in S and rBST steers. Serum urea, creatinine and cholesterol (toward the end of treatment) concentrations, however, were lower (P less than .05) in rBST steers, suggesting that nitrogen retention was increased and lipid turnover was decreased by rBST. Total (P less than .1) and conjugated (P less than .05) bilirubin concentrations and glutamate-pyruvate transaminase activity (P less than .05) were lower in rBST steers. Carcass weights were not altered, but dressing percentages were lower (P less than .05) in rBST steers. This indicated that weight gain response to rBST was primarily in noncarcass components; further examination showed that this gain was predominantly in gut fill (approximately 2/3 of the greater live weight gain in rBST steers). Alternative protocols, such as administering the hormone to younger animals and (or) for a longer duration, may be necessary in order to achieve desirable responses in carcass growth.     

Carcass composition and adipose tissue metabolism in growing sheep

Experiments were conducted to investigate biological variables that influence fat accretion in growing ram lambs. Carcass composition and adipose tissue development were measured in Columbia-sired ram lambs from 32.0 to 73.9 kg body weight. Five or six ram lambs were slaughtered every 2 mo, from 4 to 10 mo of age. The percentage of carcass fat-free dry matter decreased with age from 30.9 to 27.5% (P less than .05), while the percentage of carcass fat increased from 17.7 to 33.4%. Similarly, offal fat-free dry matter decreased with age (from 24.5 to 21.5), and there was nearly a threefold increase in the percentage of offal fat (P less than .05 for both measures). Subcutaneous adipocyte diameter and lipogenesis in vitro increased from 4 to 6 mo of age, and did not increase further with age. A bimodal distribution of adipocytes was apparent in the 4-mo-old lambs, but was not observed in any other age group. The presence of glucose in incubation media stimulated acetate incorporation into fatty acids in vitro in adipose tissue from 8- and 10-mo-old lambs. However, glucose did not affect the rate of lipogenesis from lactate. The data indicate early, rapid increases in carcass fat accretion, which corresponded to similar increases in lipogenesis and lipogenic enzyme activities.     

Dietary zilpaterol hydrochloride. II. Carcass composition and meat palatability of beef cattle

Experiments were conducted at 3 US locations (California, Idaho, and Texas) to determine the effects of dietary zilpaterol hydrochloride and duration of zilpaterol feeding on carcass composition and beef palatability. At each site, 160 steers and 160 heifers were stratified within sex by initial BW (study d -1) and assigned randomly within BW strata to 1 of 4 treatments in a randomized complete block design (4 blocks/treatment for each sex). The 4 treatments were arranged in a 2 (no zilpaterol vs. zilpaterol) x 2 (20- or 40-d duration of zilpaterol feeding) factorial. When included in the diet, zilpaterol was supplemented at 8.3 mg/kg (DM basis). Each pen consisted of 10 animals. After slaughter 2 carcasses per pen (n=64 per trial site) were selected. The entire right side of the selected carcasses was collected for dissection and chemical analysis of the soft tissue. Additionally, the left strip loin was collected for Warner-Bratzler shear force determinations and aged to 28 d postmortem. Sensory analysis was conducted on the Idaho trial site samples only. All data were pooled for analyses. Feeding zilpaterol hydrochloride increased carcass muscle deposition (P<0.01) of both steer and heifer carcasses. However, carcass percentage fat of steers and heifers was not affected (P>0.11) by the zilpaterol treatment. In heifer carcasses, carcass moisture percentage was increased (P=0.04) and bone percentage was decreased (P=0.02), whereas in steer carcasses, carcass moisture and bone percentage were not affected (P>0.10). In heifer carcasses, carcass ash percentage was not affected (P=0.61) by zilpaterol, whereas in steer carcasses, carcass ash percentage tended (P=0.07) to be increased. The protein-to-bone ratio was increased (P<0.001) by zilpaterol hydrochloride treatment in both steers and heifers, whereas the protein-to-fat ratio was not affected (P=0.10). Cooking loss of the LM was not affected (P=0.41) by zilpaterol treatment of steers or heifers. However, LM Warner-Bratzler shear force was increased (P=0.003) on average (3.3 vs. 4.0 kg) due to zilpaterol hydrochloride treatment of both steers and heifers. In both steers and heifers, LM sensory panel scores of overall juiciness (6.2 vs. 6.0), tenderness (6.2 vs. 6.0), and flavor intensity (6.2 vs. 6.0) tended (P=0.06) to be decreased in cattle supplemented with zilpaterol. Zilpaterol hydrochloride is a repartitioning agent that seems to affect carcass composition primarily through protein deposition. However, zilpaterol treatment can adversely affect tenderness and other palatability traits.     

Carcass tissue composition in light lambs: Influence of feeding system and prediction equations

Fourty-eight Churra Tensina single male lambs were used to evaluate the effect of different feeding systems on carcass composition and predict the carcass tissue composition from joint composition and carcass measurements. Four treatments were studied: GR, unweaned lambs continuously grazing with ewes; GR + S, the same as the previous group, but lambs had free access to concentrate; DRL-GRE, lambs remained indoors with free access to concentrate and ewes grazed for 8 h/day, thereafter remaining with lambs; and DRL, lambs and ewes were kept in confinement, they had free access to concentrate and dry unifeed respectively. In the DRL-GRE and DRL groups lambs were weaned when 45 days old. Lambs were slaughtered at 22–24 kg live weight. Commercial joints from the half left carcass were obtained, recorded and dissected to determine carcass tissue composition.The feeding system had an effect on the proportion of the carcass tissue composition. GR treatment showed higher muscle (M) (p < 0.05) and bone (B) (p < 0.001) percentages, and a lower total fat (F) percentage (p < 0.001) than the rest of treatments. Hence it revealed higher M/F (p < 0.01) and lower M/B (p < 0.05) and subcutaneous fat/intermuscular fat ratios (SF/IF; p < 0.001). Carcass composition predictions were more accurate for grams than for percentages. In predictions from joint composition, pelvic limb was the most accurate joint for grams (R² = 0.84, R² = 0.68, and R² = 0.77 for muscle, bone, and fat, respectively) as well as for percentage (R² = 0.65, R² = 0.56, and R² = 0.73 for muscle, bone, and fat, respectively). Predictions from carcass measurements were greater in muscle and fat grams (R² = 0.87 and R² = 0.86 for muscle and fat, respectively) than in percentage (R² = 0.58 and R² = 0.73 for muscle and fat, respectively). Equations to predict carcass tissue that include carcass measurements are a simple method to assess accurately saleable muscle yield from different lamb feeding systems without involving carcass damage.     

Physical and chemical components of the empty body during compensatory growth in beef steers

The composition of carcass and noncarcass tissue growth was quantified by serial slaughter of 26 Angus x Hereford crossbred steers (initial age and weight 289 +/- 4 d and 245 +/- 4 kg) during continuous growth (CON) or compensatory growth (CG) after a period of growth restriction (.4 kg/d) from 245 to 325 kg BW. All steers were fed a 70% concentrate diet at ad libitum or restricted levels. Homogenized samples of 9-10-11th rib and noncarcass tissues were analyzed for nitrogen, fat, ash, and moisture. Growth rate from 325 to 500 kg BW was 1.54 and 1.16 kg/d for CG and CON steers. The weight of gut fill in CG steers was 10.8 kg less (P less than .05) before realimentation and 8.8 kg more (P less than .10) at 500 kg BW than in CON steers. The allometric accretive rates for carcass chemical components relative to the empty body were not affected by treatment. However, the accretive rates for CG steers were greater (P less than .01) for noncarcass protein (.821 vs .265), noncarcass water (.861 vs .507), and empty-body protein (.835 vs. .601) than for CON steers. Final empty-body fat was lower (P less than .001; 24.2 vs 32.4%) and empty-body protein higher (P less than .001; 16.6 vs 14.8%) in CG steers than in CON steers. Consequently, net energy requirements for growth (NEg) were approximately 18% lower for CG steers. We conclude that reduced NEg requirements and changes in gut fill accounted for most of the compensatory growth response exhibited in these steers.     

Carcass traits and M. longissimus lumborum palatability attributes of calf- and yearling-finished steers

A 2-yr experiment was conducted to compare carcass characteristics and meat palatability attributes of steers ((3/4) British, (1/4) Continental) finished postweaning as calves or yearlings. Calves and yearlings of the same contemporary group were designated to a finishing system at weaning. Calves (n = 73) were finished in the feedlot (191 d) on a high-concentrate diet. Yearlings (n = 84) grazed crop residues after weaning, followed by spring and summer pasture grazing, and concluded with a short finishing period (91 d) in the feedlot. All steers were fed to a constant, fat thickness endpoint of 1 cm. The M. longissimus lumborum steaks from each production system were aged for 7, 14, or 21 d for Warner-Bratzler shear force determination and for 7 or 14 d for in-house sensory panel evaluation. Insoluble, percent soluble, and total collagen were determined. Yearlings produced heavier (P < 0.001) carcasses with larger (P < 0.001) LM areas and lower (P < 0.001) marbling scores and quality grades. Calves possessed greater amounts of total collagen (P < 0.001), with a significantly greater percentage of soluble collagen compared with yearlings (39.72 vs. 24.38%). Calves produced steaks with lower (P < 0.001) shear force values and greater (P < 0.001) sensory ratings for flavor. The USDA Choice steaks from the calves were more (P < 0.001) tender and more (P < 0.050) palatable than Choice steaks from yearlings, and USDA Select steaks from calves were rated more tender (P < 0.001), juicy (P = 0.012), and desirable (P < 0.001) than Select steaks from yearlings. As expected, increasing aging time from 7- to 14- to 21-d produced steaks with lower (P < 0.001) shear force values, regardless of the production system. Risk probabilities showed 1.24% of the steaks from calf-finished steers and 21.22% of steaks from yearling-finished steers to be tough. Sensory rating probabilities showed the steaks from the calves were most likely to be desirable for tenderness, whereas steaks from the yearlings were most likely to be undesirable for tenderness, juiciness, flavor, and overall acceptability. Thus, calf-finished steers produce carcasses superior in quality and palatability compared with those from yearling-finished steers. However, yearling-finished steers can produce tender beef with extended aging.     

Fatty acid composition of muscle and adipose tissue from crossbred bulls and steers

Fatty acid composition of total lipid extracts of muscle and adipose samples from crossbred bulls (N = 34) and steers (N = 35) was determined by gas-liquid chromatography. Samples of semitendinosus, triceps brachii and longissimus muscle and of subcutaneous and perinephric adipose tissue were excised from the right side of each carcass. In addition, thin-layer chromatography was utilized to obtain phospholipid and triacylglycerol fractions from total lipid extracts of semitendinosus and longissimus muscle and subcutaneous adipose tissue from 10 bull and steer cohorts (N = 20). The most prominent sex condition effect was in percentage of total poly-unsaturated fatty acids (PUFA). Bull tissues contained higher (P less than .01) percentages of PUFA than those of steers at all sampling sites. This reflected higher percentages of linoleate (C18:2), linolenate (C18:3) and arachidonate (C20:4) in bull tissues. Most of the PUFA were present as phospholipids in muscle samples. The fatty acid composition of muscle phospholipids was similar regardless of sex condition or muscle sampled. Total lipid extracts of semitendinosus and triceps brachii muscles of both bulls and steers contained from 6 to 10% more unsaturated fatty acids (UFA) compared with M. longissimus. Muscle triacylglycerols contained relatively high percentages of saturated fatty acids (SFA). Semitendinosus and longissimus samples from steers contained higher (P less than .05 and P less than .01, respectively) percentages of total SFA than those from bulls. Steer samples contained slightly higher percentages of palmitic acid (C16:0) compared with bulls at all sampling sites, and this difference was significant for M. longissimus. The fat:lean ratio of muscle tissue is the major factor that determines fatty acid composition.     

Visual and chemical tissue markers for bovine carcass components

A two-component, nontoxic, quantifiable animal/carcass tracing system was developed using riboflavin as an on-premises, initial carcass identifier visible under longwave ultraviolet (UV) light and deuterium oxide (D2O) as a tracer analytically quantified via fixed wavelength infrared spectrophotometry. Twenty-four cull cows and heifers were allocated into eight antemortem treatment groups (1, 12, 24, 48, 72, 96, 120, 144 h) for evaluation of the efficacy of riboflavin and D2O as tissue tracers in postmortem meat tissues. All cattle were slaughtered using conventional procedures and inspection. To study postmortem riboflavin marker changes due to constant light exposure over time, fluorescence and emission intensity scores were obtained by a trained panel 24, 48, and 168 h postslaughter. The riboflavin marker intensity rating means for UV fluorescence were classified as identifiable on all carcasses when evaluated under UV light, but were classified as not identifiable when evaluated under ambient light. Deuterium oxide levels in all tissue water samples, regardless of antemortem infusion group, contained D2O concentrations at least 2.5 times greater than those found in background water. Deuterium oxide was shown to disperse rapidly throughout living tissues. Correlations within animals for D2O levels from blood and muscle were all highly significant (r = .99).     

Effects of grazing on deposition of chemical body components, energy retention and plasma hormones in steers

The objective of this study was to evaluate the effects of grazing on the accretion of energy and chemical components in steers, using the comparative slaughter technique and taking into consideration the growth rate. Twelve Holstein steers aged 6 months and weighing 160 kg were divided into three treatment groups – an initial, grazing and control group. The initial group was slaughtered at the beginning of the experiment. The grazing group was grazed on timothy pastures for 18 weeks. The control group was kept in a stable and offered concentrate and timothy hay in a proportion of 2:1 throughout the 18 weeks. The amount of ration offered to the control group was adjusted in order to obtain a growth rate similar to that of the grazing group. The grazing and control groups were slaughtered at the end of the experiment. The grazing and the control groups had similar growth rates of approximately 0.8 kg/day throughout the experimental period and similar final live weights of approximately 260 kg. The grazing group had lower fat and energy deposition rates than the control group (P < 0.05). Deposition rates of protein, fat, ash, moisture and energy were 130, 32, 30, 374 g/day and 4.4 MJ/day, respectively, in the grazing group and 117, 85, 32, 381 g/day and 6.2 MJ/day, respectively, in the control group. The net energy for growth was lower in the grazing group (7.7 MJ/kg) than in the control group (9.9 MJ/kg, P < 0.05). The grazing group had higher plasma concentrations in growth hormone and lower plasma concentrations in insulin and insulin‐like growth factor 1 than those in the control group (P < 0.05).     

Effects of soybean oil and dietary copper on ruminal and tissue lipid metabolism in finishing steers

An experiment was conducted to determine the effects of Cu and soybean oil (SBO) supplementation on ruminal and tissue lipid metabolism and carcass characteristics in finishing steers. Sixty Angus steers (369.0 +/- 10.1 kg) were stratified by weight and randomly assigned to treatments in a 2 x 2 factorial arrangement, with factors being 0 or 20 mg of supplemental Cu/kg DM from Cu sulfate and 0 or 4% SBO. Steers were fed a high-concentrate basal diet that contained 5.3 mg Cu/kg DM. Average daily gain and feed intake were reduced (P < 0.01) by SBO but were not affected by Cu. Gain:feed ratio was not affected by treatment. Liver Cu concentrations were higher (P < 0.01) in steers receiving supplemental Cu and lower (P < 0.04) in SBO-supplemented steers. Copper supplementation tended to reduce (P < 0.12) and SBO supplementation tended to increase (P < 0.11) serum cholesterol concentrations. Backfat depth was reduced (P < 0.10) by Cu and SBO supplementation. Marbling scores and longissimus muscle lipid content were not affected by Cu supplementation; however, SBO supplementation reduced (P < 0.01) marbling scores. Longissimus muscle polyunsaturated fatty acids tended to be increased (P < 0.14) in Cu-supplemented steers. Longissimus muscle C18-conjugated dienes and the 18:1 trans isomer were increased (P < 0.05) in SBO-supplemented steers. Ruminal fluid 18:3 was increased (P < 0.05) and the 18:1 trans isomer was decreased (P < 0.05) in Cu-supplemented steers. These results indicate that as little as 20 mg of supplemental Cu/kg DM can reduce backfat and may alter lipid metabolism in steers fed high-concentrate diets.     

The composition of the broiler chicken at 56 days of age: Output,components and chemical composition

1. 24 male and 24 female broilers were slaughtered at 56 d old, eviscerated and dissected to ascertain eviscerated yield and carcass composition.

2. The chemical composition of component parts was determined by analysis.     

Effects of grass species on grazing steers: I. Diet composition and ingestive mastication.

In traditional grazing trials, per animal and per hectare productivity are determined, but pasture and animal measurements are generally inadequate to address reasons for different treatment responses. This 2-yr study examined the diet and diet characteristics of steers grazing tall fescue (Festuca arundinacea Schreb.), switchgrass (Panicum virgatum L.), flaccidgrass (Pennisetum flaccidum Griseb.), and bermudagrass (Cynodon dactylon [L.] Pers.) pastures. A randomized complete block design was used with two agronomic replicates. In vitro DM disappearance (IVDMD) of masticates from tall fescue (TF), switchgrass (SG), and flaccidgrass (FG) generally were similar; all exceeded 70% (70.3 to 79.9%), except for bermudagrass (BG), which was lowest (63.5 to 65.0%). Sieving the masticate DM showed BG to contain the highest proportion (20 to 29%) of particles passing a .5-mm sieve and the lowest proportion (6 to 8%) of particles retained on a 2.8-mm sieve. This resulted in BG having the smallest mean (1.29 mm) and median (1.08 mm) particle sizes in yr 1 and a mean (1.10 mm) and median (.91 mm) particle size smaller than SG in yr 2. Except for BG, the IVDMD of the masticate DM was lowest for small particles. Canopies showed BG and SG to have the highest proportion of stem (47 and 52%, respectively); the BG canopy was composed of fractions that were consistently lowest in IVDMD. In general, BG offered the grazing animal a canopy inferior in IVDMD concentration and had canopy characteristics that limited the animals' selection of a diet with quality as high as that of TF, SG, or FG.     

Sensory, physical, and chemical properties of pork loin chops from somatotropin-treated pigs of three stress classifications.

Forty-eight pigs of three known stress classifications were injected daily with porcine somatotropin (pST; 4 mg/d) or placebo. The effects of pST and stress classification on the sensory, physical and chemical characteristics of loin chops were observed. Chops from pST-treated animals were less tender and juicy than chops from control animals. Positive stress classification also significantly decreased juiciness but had no effect on tenderness and flavor. A significant interaction was observed for initial juiciness and sustained juiciness between chops from pST and stress-positive pigs. Whereas chops from carriers and normal pigs showed a reduction in juiciness traits with the pST treatment, among stress-positive animals both initial and sustained juiciness were increased with pST treatment. Treatment with pST had no effect on the fat, protein, and moisture content of the longissimus muscle. Furthermore, stress classification had no effect on the fat and moisture content of the longissimus muscle, but protein content was significantly higher in loin chops from stress-positive animals. Chops from pST-treated animals had significantly higher maximum shear force values, required more energy to break the sample, and had higher yield point values than chops from control animals, but stress classification did not affect the shear force values significantly. Treatment of stress-susceptible animals with pST does not lead to an increased incidence of pale, soft, exudative meat and may improve juiciness attributes of chops from stress-positive animals. However, pST treatment of animals, in this trial, led to a reduction of juiciness and tenderness of pork loin chops.     

Evaluation of urea dilution as a technique for estimating body composition of beef steers in vivo: validation of published equations and comparison with chemical composition

Urea dilution equations for prediction of empty body water in live cattle, developed by three separate groups of investigators, were evaluated by comparing empty body water calculated by these equations with that measured chemically in 6-, 12- and 18-mo-old crossbred beef steers (n = 10, 9 and 9, respectively). Of four equations for prediction of percent empty body water, one derived from mixed-breeds of steers overestimated empty body water in the 6-mo-old steers by 7.59% (P less than .05). For the 12- and 18-mo-old steers, calculated and measured percent empty body water did not differ (P greater than .05). Of seven equations for calculation of empty body water volume, two derived from Angus steers with an without live weight in the equation, and one derived from a combination of Angus and mixed-breeds of steers overestimated empty body water (P less than .05) in the 6-mo-old steers. No differences (P greater than .05) between calculated and measured empty body water volume were observed for either the 12- or 18-mo-old steers. When calculated empty body water values were regressed against that measured directly, all regression slopes were not different from 1 (P greater than .05). Intercepts from regressions involving percent empty body water (four equations) were not different from 0. Three of the seven equations for calculation of empty body water volume, one derived from bulls and the others from Angus steers had intercept estimates not different (P greater than .05) from 0. Validity required that these regressions have slopes not different from 1 and intercepts not different from 0. Empty body water calculated from equations that combined live weight and urea space were more highly correlated with directly measured empty body water than that calculated from equations derived only from urea space. Urea space correlations with body composition of our steers also were improved when live weight was included with urea space in multiple regression models. Results of this study suggest that before using any prediction equation for calculating body composition of cattle in vivo, equations should be tested with a sub-sample of cattle from the population for which its use is intended.     

Effects of compensatory growth on some body component weights and on carcass and noncarcass composition of growing lambs.

A trial was conducted in 1983 and repeated in 1984 to measure effects of restricted feed intake and realimentation on weights of organs and on carcass and noncarcass composition. A total of one hundred six weaned lambs from two breeds (Timahdit and D'man) and a breed cross (Ile de France x D'man) were used in both years. Lambs were allotted to one of six feed intake regimens: HH (ad libitum access to feed from 21 to 30 kg); HM (ad libitum access to feed from 21 to 26 kg then 70% ad libitum to 30 kg); MH (70% ad libitum from 21 to 26 kg then ad libitum to 30 kg); MM (70% ad libitum from 21 to 30 kg); LH (restricted to lose weight from 21 to 17 kg then ad libitum to 30 kg); and LM (restricted to lose weight from 21 to 17 kg then 70% ad libitum to 30 kg). Weights of visceral organs and mesenteric and kidney fat showed dramatic responses to alteration of feed allowances. After recovery from 20% live weight loss, weight of liver equaled or exceeded that of both the ad libitum and 70% refed lambs. Mesenteric and kidney fat did not. Refeeding was accompanied by an increase in water (P less than .05) and a decrease in fat (P less than .01) of both carcass and noncarcass components. These results indicate that weight loss of lambs incurred during feed shortage was largely in internal organ weights, and that these lambs can recover these losses during realimentation and undergo compensatory growth with better feed efficiency and lean carcasses.