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

Based on the potential benefits of cis-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 of cis-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 X 4 Latin square with 14d 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 ruminal cis-9-18: 1, 18: 2n-6 and 18: 3n-3 metabolism. Flows of all-trans- (Delta 4 - 16) and cis- (Delta 9 - 16) 18: 1 isomers were elevated, while increases in ruminal CLA outflow were confined to trans8,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 : 211-6 enhances ruminal outflow of trans-11-18: 1 and cis-9,trans-11-CLA in lactating cows.