Lactational performance of dairy cows fed raw soybeans, with or without animal by-product proteins, or roasted soybeans.

Twelve multiparous Holstein cows averaged 10 wk postpartum and were used in a replicated 3 x 3 Latin square design to compare two feeding strategies for increasing the ratio of dietary undegradable to degradable protein. Treatments were raw soybeans, with or without meat and bone meal plus blood meal, and roasted soybeans as the primary protein supplements. Meat and bone meal and blood meal were fed at 4.0 and .9% of dietary DM, respectively. Basal diets were 30% alfalfa silage, 18% corn silage, and 52% corn-based concentrate mix. Diets were formulated to be isonitrogenous and isocaloric. Estimated undegradable protein contents, as a percentage of total CP, were 32.2, 36.2, and 34.3 for diets containing raw soybeans, raw soybeans plus animal by-product proteins, and roasted soybeans, respectively. The undegradable protein estimates were calculated from NRC values for basal feeds and from results of in vitro analysis of test protein supplements. Yields of milk and 3.5% FCM of cows receiving raw soybeans plus animal by-product proteins (45.5 and 43.4 kg/d) and roasted soybeans (44.7 and 42.7 kg/d) were greater than those of cows receiving raw soybeans alone (43.2 and 41.3 kg/d). Increasing the ratio of undegradable to degradable dietary protein also increased yields of milk protein and fat. No differences occurred in lactation performance among cows fed the two diets containing higher undegradable protein. The DMI was not influenced by treatment. Increasing the ratio of undegradable to degradable dietary protein by feeding animal by-product proteins or heated soybeans enhanced lactation performance.