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.
- Feed intake