Digestibility and effects of three forms of mostly saturated fatty acids

Four nonlactating Holstein cows fitted with ruminal cannulas were used in a 4 x 4 Latin square design with 14-d periods. Treatments were 1) control, no added fat; 2) 5.0% prilled fatty acids (iodine value = 14); 3) 5.6% prilled hydrogenated tallow (iodine value = 8); and 4) 5.0% flaked fatty acids (iodine value = 14). Diets consisted of alfalfa haylage, corn silage, and concentrate (40:20:40, DM basis). Intake of the TMR (16.4% CP and 25.4% ADF) was restricted to 1.5% of BW so that DMI was similar among diets (9.2 kg/d). Total fatty acid intakes averaged 293, 749, 747, and 686 g/d for treatments 1 to 4, respectively. Digestibilities of total C16, total C18, and total fatty acids were greater for prilled fatty acids than for prilled hydrogenated tallow. Total tract apparent digestibilities of DM, OM, CP, ADF, and NDF did not differ among treatments. Treatments did not affect concentration of total VFA or acetate:propionate ratio in ruminal fluid. Concentration of cholesterol in plasma was lowest when cows were fed the control diet and was greater when cows were fed prilled fatty acids than when they were fed prilled hydrogenated tallow or flaked fatty acids. The three forms of saturated fatty acids did not affect nutrient digestibilities or ruminal fermentation characteristics, but the digestibility of fatty acids in prilled hydrogenated tallow was lower than in prilled fatty acids. Digestibilities of fatty acids and other nutrient fractions and characteristics of ruminal fluid generally were similar between flaked and prilled fatty acids, despite the larger particle size of flaked fatty acids.