Heat-Treated Soybean Meal as a Protein Supplement for Lactating Cows1,2

Abstract

Eighteen Holstein cows were used to evaluate the effect of heat-treated soybean meal on production and composition of milk in a 16-wk lactation trial. Cows averaged 9 wk postpartum when the trial started. Concentrate mixes containing 50% of crude protein from regular, solvent extracted or heat treated soybean meal were fed at 1kg per 3kg milk produced. Corn silage was fed ad libitum and alfalfa-brome hay at 2 to 3kg per head daily. Cows receiving heat-treated meal produced slightly more milk during the first 8 wk of the lactation period when protein intake was limiting than cows fed the extracted meal but not in the later part of lactation when protein intake by both groups was more than adequate. Percents of milk components, intakes of dry matter and gains in body weight were similar for both treatments. In a total-collection digestion trial, wk 7 and 8 of the lactation trial with six cows from each group, digestibilities of dry matter, nitrogen, energy, and fiber fractions were slightly higher for the heat-treated ration. There were no differences in rumen ammonia, volatile fatty acids, or blood urea nitrogen, although blood urea nitrogen was not elevated as much by heat-treated meal. Heat treatment of soybean meal did not alter the profile of amino acids in the arterial or venous blood serum of cows nor affect uptake of amino acids by the mammary gland.