Anabolic regulation of tissue growth in beef cattle

Abstract

The effects of anabolic implants on the regulation of tissue growth were determined in cattle fed diets varying in forage and grain content. Yearling crossbred steers (n = 117) were fed one of three diets and either not implanted or implanted (90 d intervals) with Ralgro or Synovex-S implants. Implanted steers gained faster (P < .05) and required less (P < .01) dry matter/gain than nonimplanted steers. Carcasses of implanted cattle had more (P < .05) carcass protein and retail product and less carcass (P < .05), kidney, pelvic and heart (P < .01) and longissimus (P < .01) fat than nonimplanted cattle. A trained taste panel found that steers implanted with Synovex had lower (P < .05) ratings for muscle fiber and overall tenderness than Ralgro or nonimplanted steers and that nonimplanted steers had higher (P < .01) overall palatability ratings than Synovex implanted steers. Cooked loin steaks from implanted cattle, had greater (P < .01) shear force values than steaks from nonimplanted cattle. Longissimus muscle from steers implanted with Synovex tended to have more total (P < .10) and insoluble (P < .08) collagen than muscle from nonimplanted steers. Anabolic implants increased rates of empty body (P < .05) and protein (P < .01) gain and increased (P < .01) the percentage of protein while reducing (P < .01) the percentage of fat in empty body gain. This repartitioning response was consistent for all diets, apparent at all rates of growth and increased in magnitude as the rate of empty body gain increased, suggesting that the NRC (1984) estimates of the caloric content of gain of nonimplanted vs implanted cattle need further evaluation. Reflecting the lower (P < .06) efficiency of ME use for gain, steers implanted with Synovex had lower (P < .05) NEg values than steers not implanted or implanted with Ralgro. Anabolic implants increased daily empty body protein gains of steers during growing (P < .12) and finishing (P < .03) phases. Increased rates of protein growth during the growing phase occurred through a retrieval of fat and a reduction in fat gain, while during the finishing phase the increased rate of protein deposition resulted from both repartitioning and greater rates of empty body gain. These data indicate that anabolic implants increase lean tissue growth in beef cattle.