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Lactational and Chemical Evaluation of Soybean Meals Heat-Treated by Two Methods¹

Dairy Science Department, South Dakota State University, Brookings 57007-0647

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 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 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. 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 three diets.

¹ Published with the approval of the Director of the South Dakota Agricultural Experiment Station as publication No. 1961 of the Journal Series.

² Tennessee Eastman Company, Health and Nutrition Res. Div., P.O. Box 1911, Rochester, NY 14603.