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

Abstract

A series of experiments was to evaluate regular, commercially-available solvent extracted soybean meal and soybean meal subjected to additional heat either during desolventizing or by extrusion. Soluble nitrogen (14.8, 9.3 and 7.0% of crude protein for regular, heat-treated and extruded soybean meal) 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 5 limiting amino acids (methionine, lysine, valine, leucine and isoleucine) for milk production were the same; however, relative order was altered by heat treatment for all fractions of the 3 soybean meals except that threonine replaced leucine in the insoluble fraction of extruded soybean meal and the undegradable fraction of heat-treated and extruded soybean meal. Completely mixed rations of 40% (dry matter) corn silage, 10% chopped alfalfa hay and 50% concentrate mix containing the respective protein sources, regular, heat-treated and extruded soybean meal, were fed to 10 cows each during wk 4 through 19 postpartum [Protein must be supplemented as cows can reach maximum milk production and have nutritional deficiencies]. Milk production increased when heat-treated soybean meals were fed to high producing cows with most of the increased production during the first 4 wk on the experiment (wk 4 through 7 postpartum). Increases of milk production were modest when heated soybean meals were fed to lower producing cows. Concentrations of milk fat, protein and solids as well as ruminal ammonia and blood urea were similar for cows fed the 3 diets.