Effect of incremental levels of sunflower-seed oil in the diet on ruminal lipid metabolism in lactating cows

Abstract

Based on the potential benefits ofcis-9,trans-11-conjugated linoleic acid (CLA) for human health there is interest in developing sustainable nutritional strategies for enhancing the concentration of this fatty acid in ruminant-derived foods. Most evidence to date suggests that endogenous synthesis is the major source ofcis-9,trans-11 in milk fat and ruminal outflow is limited and largely independent of dietary 18 : 2n-6 supply. Four lactating cows fitted with a rumen cannula were used in a 4 × 4 Latin square with 14 d experimental periods to examine the effects of sunflower-seed oil (SFO) as a source of 18 : 2n-6 on ruminal lipid metabolism. Cows were offered grass silage-based diets supplemented with 0, 250, 500 or 750 g SFO/d. Supplements of SFO had no effect on DM intake, milk fat or protein secretion, but increased linearly (P < 0·01) milk yield and milk lactose output and shifted (P < 0·001) rumen fermentation towards propionate at the expense of acetate. SFO supplements increased linearly (P < 0·05) the flow of 18 : 0, 18 : 1, 18 : 2n-6 and total CLA at the omasum and enhanced ruminalcis-9-18 : 1, 18 : 2n-6 and 18 : 3n-3 metabolism. Flows of all-trans- (Δ4–16) andcis- (Δ9–16) 18 : 1 isomers were elevated, while increases in ruminal CLA outflow were confined totrans-8,trans-10 and geometric 9,11 and 10,12 isomers. It is concluded that supplementing grass silage-based diets with plant oils rich in 18 : 2n-6 enhances ruminal outflow oftrans-11-18 : 1 andcis-9,trans-11-CLA in lactating cows.