Rumen passage rates and

Six ruminally cannulated steers were used to evaluate the influence of dietary concentrate level on digestion of fiber, rumen pH and fill, and liquid and particulate passage rates. Total tract digestibility of potentially digestible fiber, but not total fiber, was decreased with each increase in concentrate level. Digestion coefficients suggest that potentially digestible fiber is a more appropriate expression of diet fiber than is neutral detergent fiber in studies on effects of concentrate level on fiber digestion. Passage rate of feed components was not changed from 30 to 60% concentrate. Passage rate of roughages, but not milo or liquid, were decreased at the 90% concentrate level. Ruminal digestibility of fiber was not decreased for any ingredient from 30 to 60% concentrate, but decreased for all components at 90% concentrate. These data indicate that roughage fiber digestibility may be more severely influenced by high concentrate level than grain fiber digestibility, but that grain fiber may account for the majority of fiber digestion depression associated with feeding high concentrate diets due to its high potential digestibility, and its large contribution to total diet fiber.