Effect of dietary modification of muscle long-chain n-3 fatty acid on plasma insulin and lipid metabolites, carcass traits, and fat deposition in lambs

In a previous study we showed that feeding fish meal significantly increase d muscle long chain n-3 fatty acids (FA) and hot carcass weight. In this st udy we compared the effect of fish meal and fish oil on increasing muscle l ong-chain FA. We also investigated whether the increase in carcass weight w as due to the effect of dietary enrichment of muscle long-chain n-3 FA on m uscle membrane phospholipids and(or) to rumen by-pass protein provided by f ish meal. Forty crossbred ([Merino x Border Leicester] x Poll Dorset) wethe r lambs between 26 and 33 kg BW were randomly assigned to one of five treat ments: I) basal diet of oaten:lucerne chaff (Basal); 2) Basal + fish meal ( 9% DM) = FM; 3) Basal + fish oil(1.5% DM) with protected sunflower meal (9% DM)= FOSMP; 4) Basal + fish oil (1.5% DM)= FO; or 5) Basal + protected sun flower meal (10.5% DM) = SMP. Daily intake of ME (9.60 - 10.5 MJ ME/d) and CP (150 to 168 g/d) in all treatments was kept similar by varying the ratio of oaten:lucerne chaff and by feeding the animals at 90% ad libitum intake . Blood samples were collected at the start of the experiment and on the da y (d 42) prior to slaughter. Lambs were then slaughtered at a commercial ab attoir. At 24 h postmortem carcass traits were measured and longissimus tho racis muscle taken for analysis of FA of phospholipid and triglyceride frac tions. Lambs fed FO and FOSMP showed a marked increase in muscle long-chain n-3 FA (P < 0.001) and a reduction in magnitude of the rise in insulin con centration (P < 0.001) after feeding compared with lambs fed Basal and SMP diets. Lambs in FM had a moderate increase (P < 0.001) in muscle long-chain n-3 FA content. Compared with Basal diet, both plasma total cholesterol (P < 0.02) and high-density lipoprotein cholesterol (P < 0.001) levels were g reater in SMP and less in FO and FOSMP treatments. The i.m. fat content was reduced (P < 0.05) in FM and FO treatments, but carcass weight was increas ed only with fish meal (P < 0.03). Adding SMP to FO produced muscle with an intermediate level of i.m. fat, whereas muscle long-chain n-3 FA, i.m. fat , and insulin concentration were unchanged with SMP treatment. These result s indicate that an increase in carcass weight in FM may be due to the suppl y of ruminally undegraded protein. They also suggest that fish oil along wi th fish meal can increase long-chain n-3 FA content in phospholipid of musc le membrane. This may be associated with reduced i.m, fat content and alter ed insulin action and lipoprotein metabolism.