Softness and fatty acid composition of subcutaneous adipose tissue, and methylmalonic acid concentrations in the plasma of intensively reared lambs.

The aim of the present work was to study the relationships between lamb growth performance, soft adipose tissue and fatty acid composition of subcutaneous adipose tissue of intensively reared lambs, and to determine if the occurrence of soft fat, and of odd numbered (Odd FA) and methyl-branched-chain fatty acids in subcutaneous adipose tissue was related to plasma concentrations of methylmalonic acid (MMA). For this purpose, a sensitive gas chromatography assay to measure low plasma concentrations of MMA was developed and validated. In all, 49 male lambs were reared from 23.6 to 41.0kg. They were fed ad libitum with hay and pelleted concentrates containing either cereals (80%, C) or sugar beet pulp (70%, BP). Plasma concentrations of MMA were measured 12 days before slaughter. Softness score and fatty acid compositions of caudal adipose tissue were determined after slaughter. At the end of the trial, 75% of the carcasses had soft adipose tissue. The occurrence of soft fat appears to be related to high metabolisable energy intake per kg body weight. Soft fat was characterised by a higher water content, a lower proportion of saturated even-numbered fatty acids and higher proportions of Odd FA and methyl-branched-chain fatty acids in caudal adipose tissue, compared to firm fat. Despite high proportions of Odd FA and branched-chain fatty acids in caudal adipose tissue, plasma concentrations of MMA were low (2.02+/-1.98&mgr;mol/l). No clear relationships between MMA concentrations and soft fat or the proportions of branched-chain fatty acids other than the Iso and Anteiso acids was observed. It was concluded that the present study does not support the hypothesis that the liver's capacity to metabolise MMA was exceeded.