Raw or Extruded Soybeans and Rumen-Protected Methionine and Lysine in Alfalfa-Based Diets for Dairy Cows

Fifty-seven Holstein cows (19 primiparous) were assigned to one of four dietary treatments arranged as a 2 × 2 factorial during d 22 to 150 of lactation to examine the effects of raw or extruded (149°C) soybeans and of rumen-protected methionine and lysine supplements on lactation performance. Dietary DM contained 16.5% CP and consisted of 32.2% alfalfa silage, 5.4% alfalfa pellets, 10.4% corn silage, 38.5% high moisture shelled corn, 11.4% nitrogenous supplements, and 2.1% minerals and vitamins. From d 15 prepartum to d 21 of lactation, all cows were fed a protein supplement of raw and extruded soybeans in a 1:1 ratio. During the experimental period, an average of 18.9 kg of DM were consumed. This contained, for the amino acid-supplemented treatments, 14.2 g each of rumen-protected DL-methionine and L-lysine. Experimental data were adjusted by covariance for means measured during d 4 to 21. Dietary treatments did not affect yield of milk, milk protein or milk casein, DMI, BW and condition, or plasma urea N. Extruded soybeans depressed milk fat percentage. Evaluation of diets in continuous culture fermenters indicated no differences in digestibility of DM and carbohydrates. Ammonia N concentration in the effluent and CP degradation were lower for extruded than for raw soybean diets. Flows of NAN and total amino acids from fermenters did not differ among diets.