Rumen fermentation and lactation performance of cows fed roasted soybeans and tallow.

Sixteen multiparous Holstein cows were in a replicated 4 x 4 Latin square design with 21-d periods to examine the effects of incremental tallow addition to diets containing whole roasted soybeans on rumen fermentation and lactational performance. Total mixed rations were fed for ad libitum intake and contained, on a DM basis, 33% alfalfa silage, 12% corn silage, 14% roasted soybeans, and 41% concentrate based on ground corn and soybean meal. Treatments were 0, 1, 2, or 3% supplemental tallow. Diets contained 20% CP and ranged from 1.68 to 1.82 Mcal NEL/kg of DM. The DMI, milk yield, milk protein and fat yields, milk fat percentage, rumen acetate: propionate ratio, and in situ forage DM disappearance did not differ among treatments. A small linear decrease occurred in milk protein percentage as tallow feeding was increased (2.89 to 2.86%). Tallow supplementation increased total VFA concentration in rumen fluid and resulted in a linear decrease in rumen pH (6.17 to 5.99). Supplementation of 1 to 3% tallow to diets containing 2.8% supplemental fat from whole roasted soybeans had minimal negative effects on rumen fermentation and did not influence lactational performance.