The effect of cimaterol and oestradiol-17β alone or combined on growth and body composition of wether lambs

Abstract

ABSTRACTTwenty-four Finn ♂ × Dorset Down ♀ wether lambs about 10 weeks and weighing on average 18 kg were allocated to treatment groups as follows: untreated controls (U); 15 mg oestradiol-17β (OE) implanted subcutaneously (O); cimaterol (2 mg/kg dry matter (DM)) in the diet (C); and 15 mg OE implant + cimaterol (2 mg/kg DM in the diet) (OC). The lambs were offered a diet, restricted to 38 g/kg live weight (LW), and which contained an estimated 12·5 MJ metabolizable energy and 137 g crude protein per kg DM for the experimental period of 62 or 63 days. Comparisons were made for the main effects of OE and cimaterol and also interactions between OE and cimaterol. Treatment with OE, on average, resulted in greater LW gain, DM intake, empty body weight (EBW), body length and chest depth, weight of shoulder and loin joints and carcass crude protein, but had no effect on fat deposition in carcass or depots. As a proportion of EBW, the weights of the pituitary gland and accessory vesicular glands were increased, as was teat length in lambs treated with OE. Cimaterol treatment, on average, increased LW gain, EBW, killing-out ratio, carcass weight and its weight of crude protein and, unlike OE, decreased the weight of the pituitary gland as a proportion of EBW and reduced the weight and proportion of fat in the carcass and perirenal and retroperitoneal depots. Increases in the cross-sectional area of m. longissimus dorsi and in the weight of selected major and minor commercial joints were also obtained in cimaterol-treated lambs. The presence of significant interactions indicated that there was incomplete or no additivity between the effects of cimaterol and OE for LW gain, cross-sectional area of m. longissimus dorsi and weights of carcass and carcass crude protein, omental fat and of certain of the dissected joints. These results suggest either that the mechanisms of action of oestradiol-17β and cimaterol are not independent or that they are affected by similar metabolic or physiological processes which limit the ability of castrated male sheep to exhibit a positive response.