Characterisation of the insulin status of lambs and consequences for carcass composition.

The nutritional treatment of lambs influences the extent of carcass fat deposition. Suckled lambs deposit more fat than weaned lambs with associated increases in plasma glucose and insulin levels. To investigate the mechanisms involved, groups of lambs with different insulin profiles were created, either nutritionally or by infusing insulin, and the effect on carcass composition determined. Border Leicesterx Dorset lambs were either weaned at 5 weeks of age or remained suckling with access to grass. Twenty four lambs were slaughtered at 12 weeks of age, the remaining lambs were slaughtered at 23 weeks of age. A subset of both weaned and suckled lambs were treated with exogenous insulin from 5 weeks until slaughter. Insulin status was assessed by the glucose tolerance test and by the response of plasma glucose to injected insulin. The prolonged suckling of lambs increased carcass fatness and decreased carcass protein compared to early weaned lambs. Infusing insulin decreased carcass fatness and increased carcass protein. The alterations in carcass composition were associated with changes in the sensitivity of peripheral tissues to insuhn.