Lactational and Chemical Evaluation of Soybean Meals Heat-treated by Two Methods

A series of experiments were conducted to evaluate regular, commercially available solvent extracted soybean mean (SBM), and SBM subjected to additional heat either during desolventizing (HSBM), or by extrusion (ESBM). Soluble nitrogen (14.8, 9.3, and 7.0% of crude protein for SBM, HSBM, and ESBM) and degradable protein (71.0, 68.7, and 58.7% of crude protein) were reduced by heat-treating soybean meal. Nonessential amino acids in soybean meals were more soluble and degradable than essential amino acids. The first five limiting amino acids (methionine, lysine, valine, leucine, and isoleucine) for milk production were the same, although relative order was altered by heat treatment, for all fractions of the three soybean meals, except that threonine replaced leucine in the insoluble fraction of ESBM and the undegradable fraction of HSBM and ESBM. Completely mixed rations were made of (dry matter basis) 40% corn silage, 10% chopped alfalfa hay, and 50% concentrate mix containing the respective protein sources (SBM, HSBM, and ESBM). Milk production (33.8, 34.9, and 35.3 kg/day) was increased when heat-treated soybean meals were fed to high producing cows, with most of the increased production occurring during the first 4 wk on the experiment (wk 4 through 7 postpartum). Four percent fat-corrected milk was 30.9, 32.6, and 33.4 kg/day. Increases in milk production were modest when heated soybean meals were fed to lower producing cows. Concentration of milk fat, protein, and solids as well as rumen ammonia, and blood ammonia were similar