Forage lipid concentration, fatty acid profile and lamb productivity

Increasing the total lipid concentration and modifying the fatty acid profile in forage may increase energy intake and productivity of animals and improve the attributes of meat and milk for human health. To predict the outcome of modifying these traits in ryegrass, 3 groups of weaned lambs (n=15 per treatment) grazed ryegrass (4% total lipid) and received twice-daily oral doses of oil at 0, 28 or 56 ml/day. The oil consisted of a blend of 75% linseed oil (high in linolenic acid) and 25% sunflower oil (high in linoleic acid). For the 2 groups receiving oil the total dietary lipid concentration was increased to simulate ryegrass having medium (6%) or high (8%) total lipid. Average daily liveweight gain (238 g/day) and carcass weight (16.9 kg) were not significantly affected by lipid concentration in the diet. However, lambs eating the simulated high-lipid ryegrass ate 16% less dry matter (1285 vs 1530 g/d, P=0.07) but had 33% higher feed conversion efficiency (85 vs 64 g carcass gain/kg intake, P<0.05) than control lambs. Blood plasma and carcass meat from lambs given oils contained lower concentrations of short chain, saturated fatty acids and higher concentrations of poly-unsaturated fatty acids. These simulated changes to ryegrass indicate that modifying the lipid concentration and fatty acid profile in ryegrass could have a feed-sparing effect and improve the human-health attributes of meat from lambs finished during the spring.