Growth and metabolism in somatotropin-treated steers: II. Carcass and noncarcass tissue components and chemical composition.

Carcass and noncarcass tissue compositional characteristics were determined in growing Hereford steers treated with daily subcutaneous injections (20.6 mg/d) of recombinantly derived bovine somatotropin (rBST) for 112 d. For carcass primal cuts, weights and rates of gain of bone, lean and total fat and site of fat deposition were not significantly affected by rBST treatments with the exception of a few tissues (loin total weight, flank total and lean weight and shank total weight). Lean to fat ratios, however, were greater (P less than .1) for the loin, flank, chuck and brisket. Weights and growth of individual muscles from the hindquarter were not affected by rBST administration. Weights and(or) average daily gains of the liver, kidneys, lungs and trachea and head were greater (P less than .05) in rBST-treated animals. Weights and (or) average daily gains were greater (P less than .1) in rBST-treated steers for water in the total body and carcass, for CP in the total body and noncarcass, and for ash in the total body, carcass and noncarcass. Ratios of CP to ether-extractable fat in the total body were greater (P less than .1) in rBST steers. These data indicate that rBST modified carcass lean and fat composition in cattle, but responses were modest compared to effects of somatotropin treatment of swine.