The influence of source and level of protein, and implantation with zeranol on sheep growth

Two experiments were conducted tu investigate the influence of source of protein (fishmeal, FM versus sunflower meal, SFM), graded levels of concentrate protein supplements and implantation with zeranol on the responses of lambs fed on Themeda triandra hay ad libitum. In both experiments, 64 lambs were blocked by weight into four groups within which lambs were then randomly assigned to the 16 treatment combinations in a 2 (protein source) X 4 (protein level) X 2 (+/- implant) factorial plan. During experiment one (in which lambs were supplemented with 300 g/day of concentrate containing 94,134, 177 and 218 g crude protein/kg dry matter), no significant interactions were found. Implanted lambs had similar intakes of hay and total dry matter, and similar (P > 0.05) live weight gain (LWG) as non-implanted lambs. Lambs fed FM grew faster (P < 0.05) than those fed SFM but both groups of lambs had similar feed intakes. Both the nutrient intake and LWG increased linearly with level of concentrate protein, suggesting that protein was limiting, even in the high protein diets, During experiment two (in which lambs were supplemented with 600 g/day of concentrate containing 150, 190, 236 and 274 g crude protein/kg dry matter), lambs fed FM grew faster (P < 0,001), were more efficient (P < 0,001), and deposited more dry carcass (P < 0.01), carcass lipid (P < 0.001) and carcass protein (P = 0.06) than those fed SFM, while the linear effect of level of concentrate protein was negative for LWG (P < 0.01) and feed conversion efficiency (LWG/feed intake; P < 0.05). Implanted lambs tended to grow 13 g/day faster (P = 0.056) than non-implanted lambs. Zeranol stimulated carcass gains by increasing both the lipid and protein gains for lambs fed SFM but not for those fed FM. It was concluded that the benefit derived from implanting lambs with zeranol may be small and its cost effectiveness must be considered before it is used. (C) 2002 Elsevier Science B.V. All rights reserved.