RUMINAL DIGESTION AND DUODENAL NUTRIENT FLOWS IN DAIRY-COWS CONSUMINGGRASS AS PASTURE, HAY, OR SILAGE

The objective of this experiment was to quantitate ruminal digestion a nd flow of nutrients to the small intestine of Holstein cows grazing g rass pasture or fed grass hay or silage. Three dry, nonpregnant Holste in cows fitted with ruminal and duodenal (Y-type) cannulas grazed or w ere given free choice access to hay or silage during three consecutive 19-d periods. Pasture intake was estimated using chromic oxide; hay a nd silage intakes were both measured and estimated. Intakes were simil ar among forages. Ruminal samples had higher VFA and ammonia when cows grazed than when cows were fed hay or silage. Ruminal pH did not diff er. Based on duodenal spot sampling, cows on pasture had lower DM flow s to the small intestine. Bacterial N flow, as a percentage of total N flow, was higher for cows that grazed. Most flows of AA to the small intestine were similar among forages, but Pro and Phe were lower for g razing cows. Supplementation strategies for cows on pasture should be designed to synchronize protein and carbohydrate in the rumen and to i ncrease the supply of nutrients available in the small intestine.