NUTRIENT DIGESTION, NITROGEN, AND AMINO-ACID FLOWS IN LACTATING COWS FED SOYBEAN HULLS IN-PLACE OF FORAGE OR CONCENTRATE

Five Holstein cows in early lactation were used in a 5 x 5 Latin squar e design to study substitution of soybean hulls for portions of forage or concentrate in diets. The control diet consisted of (DM basis) 10% alfalfa hay, 40% corn silage, 25% high moisture corn, 23% protein sup plement, and 2.3% vitamins and minerals. Soybean hulls were used to re place approximately 25 and 50% of the forage or concentrate DM in the control ration. The DMI decreased linearly as soybean hulls replaced f orage. The DM and OM flow to the duodenum and apparent and true digest ion of OM in the stomach were similar among treatments. Ruminal pH was similar among treatments, but concentrations of NH3 N decreased linea rly when soybean hulls replaced forage. Total VFA concentrations were similar when soybean hulls replaced forage but showed a positive quadr atic response when soybean hulls replaced concentrate. Microbial N ave raged 59% of NAN flow and showed a negative quadratic response when so ybean hulls replaced concentrate. mows of total AA and total essential AA to the duodenum were not altered when soybean hulls were fed. Yiel ds bf milk and milk components were similar among treatments; hulls ca n be used effectively to replace forage or concentrate in lactation di ets.