Response of Lactating Cows to Pelleted and Unpelleted Soybean Meal After Partial Protein Depletion

Abstract

Twenty-four first-lactation cows, averaging 82 d postpartum, were protein depleted for 20 d by consuming a 9.4% crude protein diet. The cows were then assigned randomly and equally to a 2 X 3 factorial arrangement of dietary treatments in which either pelleted or unpelleted soybean meal containing 1% sodium bentonite was supplemented to corn or corn silage-based diets to yield 12.2, 15.4, or 18.1% crude protein, dry basis. Between 9 and 15 d of the depletion period, milk, milk protein production, and dry matter consumption decreased 20 to 25%. Blood hematocrit increased. On refeeding three amounts of protein, dry matter intake was greatest during week 4 of repletion. Milk production rapidly increased to a plateau averaging approximately 88% of preexperimental production with a somewhat greater response to the higher soybean rations. Neither intake, milk, milk protein production, plasma urea, serum albumin, or blood hematocrit provided any evidence that pelleted or unpelleted soybean meal differed nutritionally.