METHIONINE AND SOMATOTROPIN SUPPLEMENTATION IN GROWING BEEF-CATTLE

This objective of this study was to determine the effects of supplemen tal bovine somatotropin and supplemental ruminally protected methionin e (Met) on ADC, feed efficiency (FE), body composition (BC), and serum concentrations of Met, ST, IGF-I, and progesterone in growing beef ca ttle. Two experiments were conducted. In one experiment, 24 growing be ef cattle (6 steers and 18 heifers, 410 +/- 2 kg) were divided into tw o treatment groups, either controls or Met-treated animals. In a secon d experiment, 32 heifers and 8 steers (311 +/- 2 kg) were used in a co mpletely randomized design experiment (four treatments; two pens/treat ment). Treatments were arranged as a 2 x 2 factorial, with main effect s of ST (0 or 33 mu g/kg BW per day) and Met (0 or 6 g.animal(-1).d(-1 )). Feed efficiency and ADG were not affected by Met. However, ST incr eased FE and ADG (P <.05). Serum Met concentrations tended (P =.08) to increase with Met administration and remained unchanged by ST adminis tration. Serum ST and IGF-I concentrations were increased (P <.05) by ST administration but unchanged by Met administration. The BC and heif er serum progesterone concentrations were similar across treatments, a nd no interactions (P >.10) were observed between ST and Met. In summa ry, ST improved BW gain and FE. Methionine was not the first-limiting AA in the diet fed.