Recombinant growth hormone in growing lambs: effects on growth, body and carcass characteristics, hormones and metabolites

Abstract

Forty-eight crossbred wethers [Dorset Horn X (Border Leicester X Merino)] were injected subcutaneously each day for 42 to 133 days with recombinant bovine growth hormone (rebGH) at doses of either 0,50,150 or 250 pg rebGH kg-1 liveweight day-1 from 22 kg liveweight (LW) until slaughter at either 34, 42 or 50 kg LW. The lambs were fed ad libitum pellets consisting of (g kg-1 as fed) 850 lucerne, 100 barley and 50 cotton seed meal.Injections of rebGH exerted anabolic effects which were dose dependent. Overall, there were linear increases (P<0.001) in liveweight gain (LWG), total non-carcase weight, weights of heart, liver, skin, reticula-rumen, loin eye area, carcase crude protein, non-carcase crude protein, carcase ash and noncarcase ash, as well as plasma concentrations of insulin and glucose (P<0.01). There were linear decreases (P< 0.001) in feed conversion ratio, carcase weight, tissue depth (GR) and subcutaneous fat depth at the 12th rib, carcase fat and non-carcase fat as well as plasma urea. Significant interactions of dose rate with liveweight groups indicated that overall, the effects were larger in sheep grown to 50 kg than to 34 kg LW, or occurred only in the former in respect of weights of carcase, heart, liver and reticula-rumen. The same was true for depth of tissue, depth of subcutaneous fat and loin eye area at the 12th rib and also carcase and non-carcase weights of CP, fat and ash.