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 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 Ž . rations containing 55% alfalfa silage and 45% shelled corn-based concentrate dry matter basis . Ž . 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 Ž . Ž . Ž . to low: dry matter: barley 67.3% , soybean meal 63.9% , distillers dried grains 58.3% , corn Ž . Ž . Ž . Ž . gluten feed 56.9% , wheat middlings 54.6% , shelled corn 51.1% , soybean hulls 48.8% , and Ž . Ž . Ž . brewers dried grains 38.3% ; crude protein: wheat middlings 71.9% , corn gluten feed 70.3% , Ž . Ž . Ž . Ž . soybean meal 62.9% , barley 60.0% , soybean hulls 58.2% , brewers dried grains 48.9% , Ž . Ž . Ž . shelled corn 40.0% , and distillers dried grains 39.6% ; starch: wheat middlings 88% , distillers Ž . Ž . Ž . Ž . dried grains 85.5% , soybean meal 81.8% , barley 80.5% , brewers dried grains 76.0% , corn Ž . Ž . Ž . 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. q 1998 Elsevier Science B.V.