SITE OF DIGESTION AND MILK-PRODUCTION BY COWS FED FATS DIFFERING IN SATURATION, ESTERIFICATION, AND CHAIN-LENGTH

Four cannulated cows in a 4 x 4 Latin square design were used to study the effects of supplemental dietary fatty acids from roasted soybeans combined with tallow or partially hydrogenated fats, varying in ester ification and fatty acid chain length, on nutrient digestion and lacta tion performance. Diets were formulated to contain (DM basis) 48% fora ge in addition to 1.5% fatty acids from roasted soybeans and 2.5% fatt y acids from tallow, partially hydrogenated tallow triglycerides, part ially hydrogenated tallow fatty acids, or a blend of 30% tallow and 70 % hydrogenated fatty acids that were rich in palmitic acid. Apparent t otal tract digestibilities of OM, N, and NDF were similar among diets. Supplemental fat as fatty acids, compared with triglycerides, increas ed digestibilities of total fatty acids and C-18:1 in the small intest ine, perhaps indicating that lipolysis was rate-limiting. Fatty acids also increased milk fat percentage and efficiency of 4% FCM production . Although intake of C-16 fatty acids was higher for cows fed the fat rich in palmitic acid than for those fed the tallow fatty acids, total duodenal flows of C-16 fatty acids were similar, and digestibility in the small intestine was unaffected. Dry matter intake, 4% FCM product ion, and milk protein percentage were similar among treatments.