Ruminal Protein Degradation of Corn Gluten Meal in Lactating Dairy Cattle Fitted with Duodenal T-Type Cannulae

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Abstract
Four lactating Holstein cows fitted with T-type cannulae in the proximal duodenum were used in a 4 X 4 Latin square experiment to determine degradation in the rumen of protein in corn gluten meal. Cows were fed diets four times daily that contained 50% grain, 35% corn silage and 15% alfalfa hay on a dry matter (DM) basis. Corn gluten meal replaced low protein components of the grain mixture. Chromiumethylenediaminetetraacetic acid (Cr-EDTA) and La were included in portions of the grain mixtures to serve as indigestible markers for calculating nutrient flow rates and digestibilities. Grain mixtures were fed four times daily. Each experimental period was 14 d in duration and consisted of a 10-d adjustment period followed by a 4-d period for collection of feces and duodenal digesta. Mean ratios of Cr:La in the feed, duodenal digesta and feces were 5.62, 5.35 and 5.36, respectively. These results indicated that samples taken via the T-type cannula in the duodenum were reasonably representative of digesta flow past the cannula. Lanthanum was subsequently used as the sole digestibility marker for determining digesta flow rates. Apparent organic matter digestibility in the stomach averaged 41.5% and was about 30% higher when corrected for bacterial organic matter. Bacterial crude protein synthesis ranged from 15.7 to 17.7 g/100 g organic matter truly digested in the rumen. Regression of duodenal amino acid flow (y) on amino acid intake (x) indicated that 57 ± 11.1% of corn gluten meal protein left the rumen undegraded. Only 38 ± 10.8% of the lysine in corn gluten meal escaped degradation, and lysine was the most degradable of the amino acids. Copyright © 1983. American Society of Animal Science . Copyright 1983 by American Society of Animal Science