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One hundred-sixty Holstein growing-finishing steers (initial BW of 185 kg) were blocked by BW to determine the effectiveness of long-term bovine somatotropin (bST) administration on lean, skeletal, and carcass measurements. Steers were randomly allocated to 4 treatments (10 steers/treatment) within a block (n = 4 blocks). Treatments were control, no bST (C-C); bST from d 0 to 182 (bST-C); bST from d 183 to slaughter (C-bST); and bST from d 0 to slaughter (bST-bST). Steers received a s.c. injection of placebo or bST at 14-d intervals. Doses were 320 mg of bST/injection from d 0 to 112 and 640 mg of bST/injection from d 113 to slaughter. The last treatment was administered 31 d before slaughter. Steers received a 14% CP (DM basis) diet from d 0 to 182 and 11.5% CP from d 183 to slaughter that consisted of dry, whole-shelled corn and a pelleted protein-mineral supplement. Steers were slaughtered when BW per block averaged 615 kg (d 325, 353, 367, and 381 for the 4 blocks, respectively). Thirty steers were removed from the study because of poor performance with respect to their pen mates, illness, lameness, death, incomplete castration, and incorrect treatment. Serum IGF-I concentrations increased 151% (P < 0.01) from d 7 through 35 in bST-treated steers compared with control steers. During the first 182 d, bST-C and bST-bST steers were heavier (P < 0.01) and had greater (P < 0.01) ADG, G:F, hip height, and hip height gain compared with C-C and C-bST steers. From d 183 to slaughter, C-bST steers had reduced (P < 0.05) daily DMI and greater G:F than bST-C steers. At final slaughter, C-bST and bST-bST steers had greater (P < 0.05) hip height than C-C steers. Noncarcass weight was increased and dressing percent reduced (P < 0.05) in C-bST and bST-bST steers compared with C-C steers. Quality grade was least (P < 0.05) in bST-bST carcasses compared with C-C, whereas bST-C and C-bST carcasses were intermediate. At final slaughter, steers receiving bST had greater (P < 0.05) carcass protein and water composition and lower (P < 0.05) carcass lipid and lipid accretion than C-C steers. Bovine somatotropin was effective in reducing carcass fat and increasing edible lean. Administering bST to young, lightweight steers increased skeletal growth and noncarcass weight without an increase in total carcass weight, but decreased carcass quality.

Forty-one Holstein cows were injected with 0, 5, or 14 mg/d of bST for the last 46 +/- 6 d before parturition. Compared with data for controls, the 5- and 14-mg doses of bST increased apparent protein synthesis about 16% before parturition. Exogenous bST before parturition increased apparent protein degradation 30% during wk 1 after parturition. During wk 1 of lactation, 14 mg of bST also increased milk protein yield 33%. No treatment differences were present in concentration of serum NEFA, body condition score, or thickness of subcutaneous fat. Therefore, administration of bST before parturition did not alter metabolism of subcutaneous fat. Prepartum treatment with 5 and 14 mg of bST increased and maintained serum somatotropin at 6.5 and 22.7 ng/ml, respectively, compared with 1.6 ng/ml in controls. Concentrations of serum IGF-I were initially increased but were not maintained as parturition approached. On d -23, IGF binding protein 3 was increased 65% but was not different among groups by d -7. For groups administered the 5 and 14 mg/d of bST, IGF binding protein 2 was decreased 40%. Administration of bST before parturition increased protein reserves and stimulated milk protein yield for 1 wk but did not alter metabolism of subcutaneous fat. Furthermore, energy balance appeared to be a major regulator of concentrations of IGF binding protein 3 and responsiveness of IGF-I to exogenous somatotropin before parturition.

Thirty-two pigs (average weight, 74 kg) were used to determine the effects of recombinant porcine somatotropin (rpST) and dietary CP concentration on carcass and noncarcass tissues. Pigs were injected intramuscularly with either rpST (50 micrograms.kg BW-1.d-1; n = 16) or vehicle (n = 16) at 0900 for 24 d. Half the treated and control pigs were given ad libitum access to either a 14 or 20% CP corn-soybean meal diet. The left side of the carcass was physically dissected into separable skin, soft tissues, and bone. Tissue samples were obtained for enzyme assays, proximate analysis, and fatty acid profiles. Proximate analysis (fat, water, protein) of adipose tissue (AT) samples indicated that rpST decreased the percentage of ether extractable lipid (P < .01) and increased the percentage of protein and water (P < .05, P < .01) in intermuscular (IM), subcutaneous (SC), and intrafascicular (IF) AT depots and slightly altered fatty acid profiles of longissimus muscle IF and SC AT. Fatty acid synthesis and malic enzyme activity were decreased by rpST (P < .01), suggesting that lipogenesis was decreased; however, lipolysis was unaffected. Pigs fed the high-CP diet (20%) had decreased AT malic enzyme activity (P < .05) and fatty acid synthesis (P < .05). Additionally, pigs fed the high-CP diet had greater kidney weights (P < .01). Heart, liver, and kidney weights were heavier (P < .01) in pigs treated with rpST, whereas skin and total bone weight were unaffected. Neither weights nor lengths of four individual long bones were affected by dietary protein concentration or administration of rpST.

Excess fat in meat products has been identified as a dietary problem by public health officials. The meat animal industry has responded during the last 25 years to concerns about excess fat intake from animal products by implementing strategies to depress fat deposition and increase lean (protein) tissue gain in meat animals. The most successful strategy to date is the use of large, late-maturing animals for meat production. At desired market weights, these animals are much leaner than smaller, early-maturing animals. In addition, exogenous agents such as anabolic steroids (FDA approved for cattle) have been used to increase lean gain and depress fat deposition in cattle. Growth hormone (GH) and beta-adrenergic agonists (beta AA) are not yet approved by the FDA, but if/when approved would also markedly increase lean gain and depress fat deposition. Both GH and beta AA are called partitioning agents because they partition nutrients and energy toward lean (protein) accretion and dramatically lower fat deposition. Contingent on approval by the FDA and subsequent adoption of partitioning agents by the animal industry would result in meat products containing less and 30% of total calories from fat.

The relative amount of insulin-like growth factor-I (IGF-I) mRNA was determined in the liver and skeletal muscle of market weight crossbred barrows (castrated male pigs) using a solution hybridization-nuclease protection assay. Pigs were given either 50 micrograms recombinant porcine GH per kg body weight or vehicle daily for 24 days i.m. They were fed corn-soybean meal diets containing either 140 or 200 g crude protein/kg (low or high protein). The percentage of muscle in the carcasses of pigs given GH was greater (P less than 0.01) than that of controls. Relative to controls, GH increased (P less than 0.05) the amount of liver IGF-I mRNA by 2.7-fold in pigs fed the low protein diet and 3.0-fold in pigs fed the high protein diet. The amount of IGF-I mRNA in the muscles of GH-treated pigs was 77% and 84% of control pigs in those fed the low and high protein diets respectively (P less than 0.08). GH increased (P less than 0.001) the serum concentration of IGF-I 1.6-fold in pigs fed the low protein diet and 2.0-fold in those fed the high protein diet. These results indicate that the administration of GH to pigs influences the relative amount of liver IGF-I mRNA. The increased amount of liver IGF-I mRNA and the increased serum IGF-I concentrations suggest that IGF-I plays an endocrine role in mediating GH-induced muscle hypertrophy in pigs.

Twenty-one Simmental crossbred bulls (311 +/- 11 kg, 9 mo of age) were used to determine the effect of feeding 10, 12 or 14% CP on concentration of hormones in blood and the relationship of these hormones to composition of gain. Six bulls were slaughtered on d 0 to provide an estimate of initial carcass composition (9-11 rib section). Remaining bulls were assigned to dietary treatments. Blood samples were collected every 30 min from 0800 to 2000 on d 0, 66, 136 and 202 of treatment; bulls were slaughtered on d 203. Across all treatments, growth hormone (GH) declined (P less than .05) from d 0 to d 202. Free insulin-like growth factor I (IGF-I) was lowest (P less than .05) on d 0. In four randomly selected bulls, IGF-I fluctuated during the 12-h sampling periods. Within each treatment group, insulin was greatest on d 202 (P less than .05). Testosterone (T) increased from d 0 to d 66, then declined. Cortisol (C) was lowest on d 66. Thyroid hormones increased (P less than .05) after d 0. Growth hormone and IGF-I were correlated negatively with carcass fat percentage, fat accretion rate and fat thickness. IGF-I concentrations were correlated positively with percentage of carcass protein. Testosterone:cortisol ratio was not related to composition, but high T coupled with low C may be related to carcass leanness (mean carcass fat = 24.4%). These data suggest that GH and IGF-I are the hormones most related to composition of gain in growing beef bulls.

Eighty-four Holstein cows in early lactation fed diets varying in protein percent (11, 14, and 17% crude protein) and degradability in the rumen (normal and heated soybean meal) were sampled for effects on amino acids and growth hormone in blood plasma, and amino acid profiles in the duodenal digesta. Essential and branched chain amino acids in plasma increased as protein and amount of protected protein in the diet increased. These changes were accompanied by decreased concentrations of nonessential amino acids. Plasma growth hormone was highest at low protein (11.3%) probably because of decreased intakes on this diet. Molar percentages of amino acids in duodenal contents were not affected by diet suggesting that our heat-treated soybean meal influenced quantity more than quality of amino acids available for absorption in the small intestines.