Production responses obtained with supplemental protein from expeller soybean meal or corn by-products, relative to solvent soybean meal, were determined in three replicated 4 × 4 Latin square trials. Dietary forage (54 to 58% of DM) was solely alfalfa silage containing 30 to 55% DM and 21% CP (DM basis). Main concentrate ingredient was either ground shelled or high moisture corn; diets were fed as total mixed rations. In Trials 1 and 2, supplements were: control (0 CP), .6× (60% of the supplemental CP of the 1× treatment) solvent soybean meal, .6× expeller soybean meal, and 1× solvent soybean meal. In Trial 1 (DM intake=24.4kg/d), supplement had no effect on production but increased weight gain; expeller soybean meal increased production of milk and lactose relative to either amount of solvent meal. In Trial 2 (DM intake=20.0kg/d), supplement increased production of milk and milk components; milk production on .6× expeller soybean meal was greater than .6× solvent soybean meal. In Trial 3 (DM intake=22.4kg/d), distillers dried grains plus corn gluten meal replaced .6× solvent soybean meal; supplement increased production of milk, 3.5% FCM, protein, and fat with no difference among the three proteins. Across all three trials, response to supplemental protein appeared to decrease with increased DM intake. Results indicate that resistant protein from expeller soybean meal and corn by-products can replace greater amounts from solvent soybean meal, and suggest that, despite high dietary CP, absorbed protein supply may be inadequate when alfalfa silage is the sole forage.

Forty multiparous Holstein cows were assigned to a 2×2 factorial arrangement of treatments to compare heat-treated soybean meal and heat-treated whole soybeans as protein supplements and to measure the effects of 6g of supplemental niacin/d. Treatments began 10 d prior to calving and continued through 15 wk postpartum. Dry matter intake was .9 kg/d more for cows fed heat-treated soybean meal than for those fed heat-treated soybeans. The latter diet contained about 2.5% more lipid, resulting in similar daily energy intakes of 34.3 and 33.6 Mcal NE1 for heat-treated soybean meal and heat-treated soybean diets. Niacin tended to improve DM intake of cows fed diets containing heat-treated soybeans.