In situ dry matter, crude protein, and starch degradabilities of selected grains and by-product feeds

Abstract

In situ degradabilities were determined for some commonly used grains and by-product feeds in dairy cattle rations. Ingredients evaluated were barley, shelled corn, soybean meal, brewers dried grains, corn gluten feed, distillers dried grains, soybean hulls, and wheat middlings. In situ studies were conducted in three rumen-fistulated Holstein cows. Cows were fed a total mixed rations containing 55% alfalfa silage and 45% shelled corn-based concentrate (dry matter basis). Dacron bags containing 6 g (as fed basis) of each feed were immersed in duplicate at 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, and 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 grains (38.3%); crude protein: wheat middlings (71.9%), corn gluten feed (70.3%), soybean meal (62.9%), barley (60.0%), soybean hulls (58.2%), brewers dried grains (48.9%), shelled corn (40.0%), and distillers dried grains (39.6%); starch: wheat middlings (88%), distillers dried grains (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 ruminal availability. This study provides estimates of kinetics of ruminal degradation of feeds for use in dynamic models of protein and carbohydrate digestion.