Responses in the growth of body components of finishing lambs to additional metabolizable energy supplied from either grass silage or concentrates

Two experiments involving 213 finishing lambs were carried out to examine t he responses in growth rate and carcass composition to the addition of meta bolizable energy (ME) to a mixed diet in the form of either grass silage or concentrate. In the second experiment the performance of lambs offered sil age only was also compared at equal ME intake with the performance of lambs given mixed diets. On average the silages contained 224 g dry matter (DM) per kg; 148 g crude protein (CP) per kg DM; 86 g ammonia-nitrogen per kg to tal nitrogen and 723 g digestible organic matter per kg DM. Concentrates we re based on barley and soya-bean meal and contained 181 g CP per kg DM. Res ponses in carcass weight gain when additional ME was added to mixed silage/ concentrate diets in the form of grass silage and concentrates were 9.2 and 10.2 (s.e. 0.90) g/MJ respectively in experiment 1 and 9.8 and 10.8 (s.e. 0.33) g/MJ respectively in experiment 2, and responses in energy retention in experiment 2 were 0.34 and 0.37 (s.e. 0.012) MJ/MJ respectively. However carcass gain and energy retention sustained by a silage only diet were onl y 0.67 and 0.70 respectively of those sustained by a high-concentrate diet at the same ME intake. The diet did not significantly affect body or carcas s composition.