Influence of Amount of Feed Intake and Forage Physical Form on Digestion and Passage of Prebloom Alfalfa Hay in Dairy Cows

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Abstract
Six Holstein cows were fed prebloom alfalfa hay in long, chopped, and pelleted form (60:40 hay:grain ratio) in a replicated 3 .times. 3 Latin square design (21-d periods) conducted in early (wk 3 to 11) and middle (wk 20 to 32) lactation and during the dry period to attain three feed intakes for determination of digesta kinetics. Dry matter intakes averaged 3.75, 2.93, and 1.95% of body weight across intakes. There was no effect of forage physical form on intake or milk production. Chewing activity, ruminal fermentation patterns, and milk fat percent were similar for long and chopped hay treatments. Digestibility of organic matter was reduced 7.9% at high versus low intake and 3.2% when pelleted rather than long hay was fed. Ruminal retention time of ytterbium applied to hay declined with increasing feed intake. There was no effect of chopping or grinding on rumen dry matter fill or retention time of ytterbium applied to hay. Effects of forage physical form on retention time and ruminal fill appear small when low fiber alfalfa is fed. Digestibility depression associated with fine grinding of high quality alfalfa was related to depressed ruminal digestion rate. Digestibility depression at high intake was related to shortened ruminal residence time.