THE EFFECT OF CONCENTRATE ON THE DIGESTION OF BROMEGRASS CONSTITUENTS

Abstract

A nylon bag technique was used to study the effect of concentrate feeding on the rate and extent of digestion of bromegrass constituents in eight fistulated sheep fed rations at or slightly above maintenance, at concentrate to bromegrass ratios of 3:97, 22:78, 44:56 and 66:34. The eight sheep were arranged in a double 4 × 4 latin square design with nylon bag incubation times of 3, 6, 12, 24 and 48 h. Rations containing 44 and 66% concentrate depressed rumen digestion of bromegrass dry matter at both 24- and 48-h incubation times. The extent of digestion depression varied among sheep and was related to the animal's ability to buffer increases in rumen acidity. Digestibilities of neutral detergent fiber, acid detergent fiber, cellulose and hemicellulose followed trends similar to that of dry matter. Rumen osmolality, total volatile fatty acids and ammonia levels appeared to have little relationship to bromegrass dry matter digestion. The apparent or total gut digestibility of cell wall components was not depressed. This suggested that additional digestion took place in the ileum, cecum and colon and that the proportion of concentrate supplementation may affect ruminal but not the total gut utilization of roughage at maintenance levels of intake.