Fatty acid flow to the duodenum and in milk from cows fed diets that contained fat and nicotinic acid

Four cows fitted with ruminal and duodenal cannulas were used in a 4 x 4 Latin square design; treatments were arranged in a 2 x 2 factorial. Treatments were 1) low fat diet, no nicotinic acid; 2) low fat diet, 12 g/d of nicotinic acid; 3) high fat diet, no nicotinic acid; and 4) high fat diet, 12 g/d of nicotinic acid. Cows were fed for ad libitum intake diets consisting of 35% alfalfa silage, 15% corn silage, and either 50% low fat concentrate or 40% high fat concentrate (tallow supplied 6.25% of concentrate) and 10% whole raw soybeans (dry matter basis). Intake of gross energy (104 Mcal/d) was not different among treatments. Ruminal and postruminal digestibility of energy was not altered by fat or nicotinic acid. Fatty acid intake and flow to the duodenum were increased by fat but were not affected by nicotinic acid. For all diets, flows to the duodenum of C16:0, C18:0, total C18, and total fatty acids increased, and flows of C16:1, C18:1, C18:2, and C18:3 decreased, compared with their intakes. Biohydrogenation of unsaturated C18 was decreased by fat but was not affected by nicotinic acid. Digestibilities of C18:0, C18:1, C18:2, C18:3, and total fatty acids that flowed to the duodenum were decreased by fat but were not affected by nicotinic acid. The yield of C18:0 in milk was increased, and yields of C6:0 to C16:0 fatty acids were decreased, by fat, but yields were not affected by nicotinic acid.