Diets containing high oil corn and tallow for dairy cows during early lactation.

Four multiparous Holstein cows averaging 49 DIM and fitted with ruminal cannulas were utilized in a 4 x 4 Latin square design with 21-d periods to determine the effects of diets containing high oil corn grain and tallow. Cows were fed diets of alfalfa haylage and concentrate (37:63, DM basis) for ad libitum intake. Treatments were 1) control, no added fat; 2) high oil corn grain replacing regular corn grain; 3) high oil corn grain and 2.5% tallow; and 4) high oil corn grain and 5% tallow. Intake of DM, milk production, and yields of milk fat, milk protein, milk SNF, and 4% FCM were not affected by dietary fat, although DMI tended to be lower when cows were fed 5% tallow. Percentages of protein and SNF in milk were lower when cows were fed diets containing fat. Percentage of milk fat was lower when cows were fed diets containing tallow. Supplemental fat decreased total VFA concentrations in ruminal fluid. Cows fed high oil corn had a greater molar proportion of acetate and a larger acetate to propionate ratio in ruminal fluid than cows fed high oil corn and tallow. Digestibility of total fatty acids decreased when tallow was added to diets containing high oil corn. No differences were observed among treatments for total tract apparent digestibilities of DM and fiber or utilization of energy and N. Dietary high oil corn and 5% tallow tended to decrease DMI and to alter ruminal fermentation characteristics.