Effects of Beet Pulp and Animal By-Products on Milk Yield and In Vitro Fermentation by Rumen Microorganisms

Forty-six Holstein cows (30 primiparous) were assigned to one of four dietary treatments arranged as a 2 × 2 factorial experiment during wk 4 to 17 of lactation. Main effects were corn versus dried sugar beet pulp and soybean meal versus animal by-product meal (mixture of meat and bone meal, feather meal, and blood meal). Beet pulp replaced half of the corn at 15% of dietary DM. Diet DM (mean of four treatments) contained 18% alfalfa pellets, 17.4% alfalfa hay, 17.2% corn silage, and 47.1% concentrate. Milk yield did not differ among treatments (mean 32.0 kg/d). Dry matter intake, milk CP percentage, and milk CP yield decreased 5.6, 3.7 and 5.2%, respectively, but milk fat percentage increased 4.7% when beet pulp replaced corn. Animal by-products did not affect DMI or milk fat, but milk CP percentage decreased 3.0%. The same diets were evaluated in a continuous culture system. Fungal extract (Aspergillus oryzae), added as the third treatment, had little effect on fermentation. Digestion of DM, OM, NDF, and ADF were not affected by dietary treatments. Molar proportion of acetate was greater when corn was replaced by beet pulp. Although flow of NAN from fermenters increased by 3.2% with beet pulp and 3.1% with animal by-products, milk CP percentages decreased.