PERFORMANCE, CLINICAL-CHEMISTRY, AND CARCASS RESPONSES OF FINISHING LAMBS TO FORMULATED SOMETRIBOVE (METHIONYL BOVINE SOMATOTROPIN)

Formulated zinc methionyl bST (sometribove, 50, 100, or 150 mg) was ad ministered as a single treatment once every 2 wk or as two equal treat ments once/week to evaluate the efficacy of prolonged release delivery of bovine somatotropin (bST) in finishing lambs. Feed conversion duri ng the 6-wk treatment period was improved 9 and 19% in lambs that rece ived treatments once and twice/2 wk, respectively (P < .05), and the r esponses to differing doses were similar within a dosing frequency (P > .05). Carcass muscle: fat ratio indicators generally were affected i n a dose-related manner and were independent of frequency of administr ation. For example, fat thickness was 17, 30, and 42% lower than contr ol in lambs that received 50, 100, and 150 mg of formulated sometribov e/2 wk, respectively (P < .05). Percentages of muscle were higher and of fat were lower with increasing dose of formulated sometribove, but weight of only fat was significantly affected (P < .05). Clinical chem istry indices of metabolic effects of bST (e.g., circulating bST, IGF- I, insulin, glucose, and urinary nitrogen concentrations) were affecte d in directions similar to those observed with bST administered by dai ly injection. The results of this study demonstrate the growth perform ance and carcass composition advantages of a formulation designed to d eliver bST over a 2-wk period.