Heat-Treated Soybeans for Lactating Cows

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Abstract
An experiment with 12 cows in switchback design determined the feeding value of a heat-treated soybean product. Treatments were regular soybean meal with 44% crude protein, commercially available heat-treated soybeans and unheated soybeans. Concentrate mixes of protein sources and corn were formulated to contain 15% crude protein and fed at 1 kg/3 kg milk. Forage portion of the diet consisted of 2.3 kg alfalfa hay/day and corn silage ad lib. N solubilities of the protein supplement sources in 10% Burroughs'' buffer solution were 13.8, 9.4 and 25.4%, and averaged 29.4, 28.9 and 33.2% for the total rations. Cows averaged 7 wk post partum at the start of the experiment, which consisted of three 4-wk periods. Production of milk was similar for all treatments. Means for cows fed soybean meal, heat treated soybeans and unheated soybeans were 28.6, 29.1 and 28.3 kg/day. No differences were in milk fat (3.57, 3.61 and 3.53%) or total solids (12.16, 12.12 and 12.13%). Protein percent in milk was lower for heat-treated and unheated soybeans (3.00, 2.92 and 2.93%), probably because of the higher fat content of those diets. Amounts of long chain unsaturated fatty acids in milk fat were higher for soybean diets. Heating soybeans improved their value slightly as a feed for lactating cows, but milk production by cows past peak production was not significantly greater than production with conventional corn-soybean meal diets.