Nutrient Digestibility of Lower-fiber Rations in the Ruminant Animal

Abstract

Digestibility trials with growing steers related chemical composition as defined by detergent analyses to true and apparent digestible components in 14 lower-fiber rations. Linear relationships were significant when the digested fraction of a constituent was regressed on the total constituent consumed in the rations for cell-wall constituents, cellulose, hemicellulose, neutral detergent solubles, and nitrogen fractions, with less nutritive uniformity in the fibrous fractions. Total ration cellulose explained 77% (coefficient of determination) of the variation in digestible cellulose while lignification constituted only 20%. Total hemicellulose explained 5970 of the variation in digestible hemicellulose with a small contribution (670) from lignification. Decreased apparent digestibility of detergent solubles or increased fecal loss of nonfibrous energy were related to increased cell-wall fiber in the ration. Correlation (r = .97, P < .01) between digestible and total N indicated nutritive uniformity among N sources which included urea. Fecal N loss in nmainant animals was controlled by amount of ration N and composition of ration dry matter. A larger metabolic fecal protein excretion was associated with cell-wall N than with detergent soluble N (2.2 and 1.77o of ration DM). Apparent digestible dry matter was related to fecal endo-