Influence of duodenal infusion of nicotinic acid on the milk fat composition of dairy cows

Two experiments I and II, with 2 and 4 lactating dairy cows respectively, each fistulated with ruminal and duodenal cannulae, were carried out. The effects on milk composition and milk fat fatty acids' pattern through a continous daily infusion into the duodenum with 6 g nicotinic acid were investigated. Treatments were nicotinic acid (NA) infusion in experiment I, and nicotinic acid infusion plus feeding 270 g of stearic acid in experiment II. No application of NA and stearic acid in experiments I and II respectively, acted as controls. Nicotinic acid infusion did not significantly influence protein, fat and lactose contents of milk. In both experiments, infusion of nicotinic acid decreased the proportion of short and middle chain fatty acids in milk fat and increased significantly the percentage of oleic acid from 19.0 to 25.4%. The addition of stearic acid alone had no effect on milk composition and fatty acids' pattern. Additional infusion of nicotinic acid infusion significantly increased nicotinamid concentration in the milk from 49.7 to 87.2 mu g/100 ml.