Recombinant growth hormone in growing lambs: effects on growth, feed utilization, body and carcass characteristics and on wool growth

Abstract

Groups of six crossbred lambs, three wethers and three ewes, about 22 kg liveweight (LW), were injected subcutaneously with 0, 50, 150 and 250 pg (kg LW) d a y 1 of recombinant DNA-derived bovine growth hormone (rebGH) for 60 days. From blood sampled twice weekly 4.5 h after injection, the mean plasma concentrations of growth hormone (GH) (P<0.01) and insulin (P<0.05) were significantly increased. The mean concentrations of GH were 2.9, 7.1, 9.4 and 8.8 8g/l, while insulin concentrations were 24.2, 29.5, 46.8 and 68.2 mU/l for the respective treatments. Maximum concentrations of plasma GH were recorded about 3 h after injection. Rates of liveweight gain were 180, 217,238 and 261 g/day (P<0.001), fccd conversion ratios were 5.71,4.97,4.66 and 4.05 g feed/g gain ( P < 0.001), and warm carcase weights were 14.4, 16.4, 16.6 and 16.8 kg (P < 0.0 1) for the respective treatments. The linear change in warm carcase weights became a quadratic response (P<0.05) when adjusted to an empty body weight (EBW) of 28.8 kg. Wool growth was not affcctcd by treatments. Of the non-carcase components, major organs including the head (P<0.01), feet (P<0.05), heart (P<0.05), liver and gallbladder (P < 0.05), reticula-rumen (P < 0.05), omasum (P<0.05) and blood (P<0.01) showed linear increases in weight with increasing dosage of rebGH, but no significant differences when data were adjusted to a standard EBW. The chemical composition of the carcase showed that crude protein increased linearly (P<0.001) with increasing doses of rebGH. When adjusted to 28.8 kg empty body weight, there was 16.0�/o more carcase protein (P<0.01) with 250 than with 0 8g (kg LW)-1 day-1 of rebGH.