Effect of processing of dietary barley and of supplementary cobalt and cyanocobalamin on the fatty acid composition of lamb triglycerides, with special reference to branched-chain components.

I. The possibility that, when lambs are fed on barley-rich diets, vitamin Bla might limit hepatic utilization of propionate and result in the formation of branched-chain fatty acids was investigated with thirty-six animals allocated to twelve treatments according to a 3 x z x 2 factorial design. 2. From 13 kg live weight to slaughter at 35 kg the lambs were given diets containing barley in one of three physical forms, and one of two levels of cobalt (0.1 and 09 mg/kg diet). In addition, half the lambs received twice-weekly injections of cyanocobalamin (40 ,ug/kg body-weight). 3. The fatty acid composition of triglycerides from subcutaneous and perinephric adipose tissue was determined at slaughter. 4. Neither additional dietary Co nor the administration of cyanocobalamin (alone or in combination with additional Co) influenced the proportions of branched-chain acids in the triglycerides. The possibility is discussed that the ability of the lamb to respond to the increased supply of propionate which is provided by a high-barley diet is not restricted by the availability of cyanocobalamin, but by hepatic capacity to utilize it for the production of methylmalonylCoA mutase (EC 5.4.99.2). 5 . Regardless of diet, subcutaneous triglycerides contained greater proportions of propionate-derived fatty acids than did perinephric triglycerides which contained greater proportions of exogenously-derived CIS unsaturated acids. Lambs given whole barley in loose mix produced triglycerides containing relatively less odd-numbered n-acids and branchedchain acids than did lambs fed on either of two pelleted diets containing rolled or whole barley.