EFFECTS OF SYNOVEX-S(R) AND RECOMBINANT BOVINE GROWTH-HORMONE (SOMAVUBOVE(R)) ON GROWTH RESPONSES OF STEERS - III - MUSCLE GROWTH AND PROTEIN RESPONSES

We conducted this study to determine whether the growth responses of s pecific skeletal muscles in crossbred beef steers were differentially affected by treatment with recombinant bovine growth hormone (Somavubo ve(R), SbV, .1 mg/kg BW, i.m., daily), Synovex-S(R) (200 mg progestero ne + 20 mg 17-beta estradiol benzoate, SYN, ear implant), or a combina tion of the two. Starting body weights of steers averaged 182 +/- 1.8 kg. Five steers were used at this average BW to obtain data on weight and composition of individual muscles at d 0, and 20 other steers were assigned in equal numbers to control (C, no implant and placebo daily injection), SYN, SbV, and SYN + SbV treatment groups. After 56 d of t reatment with placebo or growth promoters, complete rectus femoris (RF ), triceps brachii (TB), supraspinatus (SS), psoas major (PM), and sem itendinosus (ST) muscles were dissected, weighed, and then ground for determination of moisture, total protein, and fat. To calculate the av erage daily muscle wet weight, protein, and fat gains, the initial wei ght, protein content, and fat content of a muscle were subtracted from those obtained at slaughter and the difference divided by 56. Muscle weight was increased over C in TB and SS by SYN (P < .1); in TB by SbV (P < .09); and in RF (P < .05), TB (P < .03), and SS (P < .03) by SYN + SbV. Overall average daily wet tissue gain was increased over C by SbV + SYN (P < .05) in RF, TB, and SS. Average daily protein gain in R F and TB was increased by SYN (P < .1), SbV (P < .06), and SYN + SbV ( P < .01) over that calculated for C. For RF, TB, and SS, average daily protein gain was greater (P < .1) in SbV + SYN than that obtained wit h SbV or SYN alone. These data suggest that administration of growth p romoters, such as somatotropin and Synovex, to cattle differentially a ffects growth characteristics in certain muscles and can have additive effects on protein gain when used together.