Effect of Diets Containing n–3 Fatty Acids on Muscle Long-Chain n–3 Fatty Acid Content in Lambs Fed Low- and Medium-Quality Roughage Diets

Source: E. N. Ponnampalam, A. J. Sinclair, A. R. Egan, S. J. Blakeley, and B. J. Leury

In two experiments, each with 32 cross-bred ([Merino × Border Leicester] × Poll Dorset) wether lambs (26 to 33 kg weight range), animals were randomly assigned to one of four treatments. A mixture of lucerne chaff:oaten chaff was used as a basal diet, offered in different ratios. Animals were allowed to consume on a free-access basis in Exp. 1 or 90% of ad libitum intake in Exp. 2 in order to provide a low- (6.5 MJ ME/d) and medium- (9.5 MJ ME/d) quality basal diet, respectively. Isoenergetic amounts of lipid supplements, fish meal (80 g DM), canola meal (84 g DM), and soy meal (75 g DM) were tested in Exp. 1. In Exp. 2, fish meal (9% DM), unprotected rapeseed (7% DM), and protected canola seed (6% DM) were fed as supplements. At the end of 53-d (Exp. 1) or 46-d (Exp. 2) experimental periods, lambs were slaughtered at a commercial abattoir and at 24 h postmortem longissimus thoracis (LT) muscle was collected for the analysis of fatty acid (FA) composition of structural phospholipid and storage triglyceride fractions. Fish meal diet increased LT muscle long-chain n–3 FA content by 27% (P < 0.02) in Exp. 1 and 30% (P < 0.001) in Exp. 2 compared with lambs fed the basal diet, but fish meal decreased (P < 0.01) the n–6 FA content only in Exp. 1. Soy meal and protected canola seed diets increased (P < 0.01) LT muscle n–6 FA content but did not affect long-chain n–3 FA content. Longissimus thoracis muscle long-chain n–3 FA were mainly deposited in structural phospholipid, rather than in storage triglyceride. In both Exp. 1 and Exp. 2, the ratio of n–6:n–3 FA in LT muscle was lowest (P < 0.01) in lambs fed fish meal supplement compared with all other treatments. Protected canola seed diet increased the ratio of n–6:n–3 FA (P < 0.01) and PUFA:saturated fatty acid (P < 0.03) content from those animals fed the basal, fish meal, and unprotected rapeseed diets in Exp. 2. This was due to an increase in muscle n–6 FA content, mainly linoleic acid, of both phospholipid (P < 0.001) and triglyceride (P < 0.01) fractions and not to an increase in muscle n–3 FA content. The results indicate that by feeding fish meal supplement, the essential n–3 FA can be increased while lowering the ratio of n–6:n–3 content in lamb meat to an extent that could affect nutritional value, attractiveness, and the economic value of meat.