Co-product fiber digestibility: kinetic and in vivo assessment

Nutrient digestion and kinetic characteristics of alfalfa hay, brewers grains, beet pulp, and cottonseed hulls were studied in two experiments. In the first experiment, these feedstuffs were fed with a mineral/vitamin supplement in a 4 x 4 Latin square to eight ewes to determine total tract digestibilities by 8-d total collection and rates of passage using Yb as a marker. In the second experiment samples of the same feedstuffs were incubated in situ in four ruminally fistulated steers in a 4 x 4 Latin square design to quantify ruminal disappearance of NDF and ADF. Three Dacron bags were placed in the rumen for each of six time periods: 6, 12, 24, 48, 72, and 96 h. Total tract digestibilities of DM ranged from 33% for cottonseed hulls to 78% for beet pulp. Digestibilities of NDF ranged from 32% for cottonseed hulls to 81% for beet pulp. Total tract retention times ranged from 74 h for beet pulp to 44 h for alfalfa. Retention time for alfalfa was lower (P < .05) than those for beet pulp or cottonseed hulls. Calculation of TDN values yielded values similar to those of NRC other than for cottonseed hulls, for which NRC values were 18 to 29% higher. Alfalfa hay and beet pulp were the feedstuffs with the most rapidly disappearing NDF, .124/h for alfalfa and .116/h for beet pulp, which were faster (P < .05) than those found in brewers grains and cottonseed hulls, .035 and .043/h, respectively. Potentially digestible NDF ranged from 55% for alfalfa hay to 94% for beet pulp.(ABSTRACT TRUNCATED AT 250 WORDS)