Influence of supplemental tryptophan and zeranol implantation on performance, carcass composition, serum hormones and nutrient utilization by lambs

In Expt. 1, treatments were two levels zeranol (0, 12 mg implant) and three levels tryptophan (TRP: 0, 0.5, and 1% DM of diet) in a factorial design. Tryptophan and zeranol interacted (P < 0.05), such that lambs receiving 0.5% TRP only and lambs receiving 1% TRP plus zeranol had greater (P < 0.05) OM intakes than did lambs receiving 0.5% TRP plus zeranol. No treatment interactions or treatment effects were noted (P>0.10) for daily gain, feed efficiency, and serum melatonin concentration. Zeranol increased (P<0.06) insulin on d 42 and had minor effects on carcass composition. In Expt. 2, lambs were fed diets containing 0 or 0.5% supplemental TRP. No effects of TRP were noted (P>0.10) for DMI, digestibility, and N balance. Lambs fed TRP had lower (P<0.09) serum insulin concentration, but TRP did not affect somatotropin or prolactin concentrations. It is concluded that tryptophan supplementation up to 1% of dietary DM does not alter metabolism in a manner causing differences in performance, digestion or carcass characteristics.