EFFECT OF CIMATEROL IMPLANTS ON LAMB GROWTH AND CARCASS TRAITS

In a series of experiments, involving 372 lambs over 2 years, the effects of subcutaneous implants of Cimaterol (CL263, 780; anthranilonitrile, 5-[1-hydroxy-2-(isoproplyamino)ethyl]-), in young sheep grazing pasture were examined. Treatment with Cimaterol increased carcass weight gain by 37% averaged over the experiments. Wool growth was reduced by 16% in the experiments where it was measured. Cimaterol treatment also increased dressing percentages by 1.3-3.7 percentage units, increased the cross-sectional area of L. dorsi muscle, and decreased fat depot weights and subcutaneous fat thickness measurements in all experiments. These changes were accompanied by increased protein and water contents and a decreased fat content in the carcass. Analysis of the growth rates of carcass components revealed that the changes were a consequence of marked increases in the rates of carcass protein deposition (up to c. 3-fold) in Cimaterol-treated lambs accompanied by markedly reduced rates of lipid deposition. Cimaterol treatment at a higher dose rate (1.8 versus 0.9 mg/head per day) gave equivalent or slightly larger responses in fat and protein deposition. In one experiment, treatment for 12 weeks gave slightly better responses than for 6 weeks particularly at the lower dosage rate. Finally, the effect of Cimaterol treatment, expressed in percentage terms, was remarkably consistent over a range of ages, carcass weights, breeds, sexes, and nutritional levels commonly found in pastoral sheep production systems. © 1990 Taylor & Francis Group, LLC.