IN-SITU DRY-MATTER, CRUDE PROTEIN, AND STARCH DEGRADABILITIES OF SELECTED GRAINS AND BY-PRODUCT FEEDS

In situ degradabilities were determined for some commonly used grains and by-product feeds in dairy cattle rations. Ingredients evaluated we re barley, shelled corn, soybean meal, brewers dried grains, corn glut en feed, distillers dried grains, soybean hulls, and wheat middlings. Ln situ studies were conducted in three rumen-fistulated Holstein cows . Cows were fed a total mixed rations containing 55% alfalfa silage an d 45% shelled corn-based concentrate (dry matter basis). Dacron bags c ontaining 6 g (as fed basis) of each feed were immersed in duplicate a t each time point in the ventral rumen of each cow for 2, 4, 6, 12, 24 , 48, and 72 h. Ruminal availabilities of dry matter, crude protein, a nd starch calculated as a percentage of nutrient were ranked from high to low: dry matter: barley (67.3%), soybean meal (63.9%), distillers dried grains (58.3%), corn gluten feed (56.9%), wheat middlings (54.6% ), shelled corn (51.1%), soybean hulls (48.8%), and brewers dried grai ns (38.3%); crude protein: wheat middlings (71.9%), corn gluten feed ( 70.3%), soybean meal (62.9%), barley (60.0%), soybean hulls (58.2%), b rewers dried grains (48.9%), shelled corn (40.0%), and distillers drie d grains (39.6%); starch: wheat middlings (88%), distillers dried grai ns (85.5%), soybean meal (81.8%), barley (80.5%), brewers dried grains (76.0%), corn gluten feed (70.6%), soybean hulls (66.4%), and shelled corn (56.5%). Grains and by-product feeds vary widely in their rumina l availability. This study provides estimates of kinetics of ruminal d egradation of feeds for use in dynamic models of protein and carbohydr ate digestion. (C) 1998 Elsevier Science B.V.