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Abstract
Bárcena-Gama, R., Swingle, R.S., Moore, J.A. and Poore, M.H. 2002. Effect of roughage source on ruminal kinetics and passage of individual feed components in finishing diets for steers. J. Appl. Anim. Res., 21: 109–121.
Two 4 x 4 Latin square experiments were conducted to determine the effect of substituting chopped alfalfa hay (AH) in a diet containing 10% AH (DM basis) for chopped wheat straw (WS), chopped bermudagrass straw (BS) or cottonseed hulls (CSH), on diet utilization and kinetics of ruminal digestion and passage of roughage and grain. In experiment 1, total tract digestion coefficients for dry matter (DM), neutral detergent fiber (NDF) and starch were determined. Particulate passage rates for grain and roughages in each diet (rare earth metals) and liquid dilution rate (Co-EDTA) were also measured. In experiment 2, four mature ruminally cannulated steers were used to determine kinetics of in situ ruminal digestion of DM, NDF and starch for milo and roughage components of the diets. Replacing AH by low quality roughages depressed (P>0.05) total tract digestion of DM and NDF but not for starch. Potential extent of digestion (72 h in situ) of DM for milo was lower (P>0.05) in the CSH diet. The extent of digestion for DM and NDF were higher (P>0.05) for AH than for the lower quality roughages. Diets containing WS or BS promoted a higher (P>0.05) raft formation than AH or CSH diets. The AERD for DM and NDF from milo was not affected (P>0.05) by roughage source and ruminal pH did not differ (P>0.05) among diets. These results suggest that substitution of AH for low quality roughages depresses total tract digestibility and that the effect on kinetics of ruminal digestion and passage for the grain fraction was minimal. However, the data also suggest that inclusion of WS in 90% concentrate diets may function to improve rumen conditions for NDF digestion and to reduce the incidence of metabolic acidosis.