Milk composition, ruminal characteristics, and nutrient utilization in dairy cows fed partially hydrogenated tallow.

Four Holstein cows (84 DIM) were used in a 4 x 4 Latin square with 21-d periods to determine the effects of increasing amounts of partially hydrogenated tallow in the diet. Tallow replaced ground shelled corn at 0, 2, 4, or 6% of total DM; diets contained 3.3, 5.1, 7.3, and 9.0% total fatty acids. Feces and urine were collected during d 16 to 21 of each period. Milk production (31.1, 31.7, 34.6, and 32.8 kg/d), milk fat content, and DMI (21.2, 20.8, 22.2, and 21.5 kg/d) were not significantly different among diets supplemented with 0, 2, 4, or 6% tallow. Tallow decreased contents of CP and SNF in milk but increased production of NPN. Percentages of short- and medium-chain fatty acids in milk fat decreased linearly, whereas percentage of C18:1 increased with increasing dietary tallow. Ruminal pH, concentrations of total VFA and NH3 N, molar percentages of VFA, and acetate to propionate ratio did not differ among treatments. Total tract apparent digestibilities of DM, OM, NDF, ADF, cellulose, hemicellulose, ether extract, energy, and soluble residue did not differ among treatments. Digestibility of total fatty acids decreased in diets containing tallow. Increasing tallow linearly increased N apparently absorbed, but utilization of energy and N was not significantly different among treatments. Partially hydrogenated tallow included at 6% or less of dietary DM did not adversely affect DMI, digestibilities, or ruminal fermentation characteristics.