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Nutrient Digestibility of Lower-fiber Rations in the Ruminant Animal^{1, 2,}

Department of Animal Sciences, Rutgers University, New Brunswick, New Jersey 08903

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 59% of the variation in digestible hemicellulose with a small contribution (6%) 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 ruminant 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 1.7% of ration DM). Apparent digestible dry matter was related to fecal endogenous loss of detergent solubles and N and to total cell-wall fiber, whether constituted mostly by cellulose or hemicellulose, in the ration. Cellulose, acid-detergent lignin, and cell wall fractions were inversely correlated (P < .01) to digestible dry matter; however, hemicellulose was not. Total N was not related statistically to digestible dry matter, but detergent soluble N (positive, P < .05) and cell wall N (negative, P < .01) were.

¹ Paper of the Journal Series, New Jersey Agricultural Experiment Station, Rutgers Univesity, New Brunswick 08903.

² Data in this paper are from a thesis submitted by the senior author in partial fulfillment of requirements for the degree of Doctor of Philosophy. The senior author wishes to thank the University of Puerto Rico Agricultural Experiment Station for support during this study.

³ Present address: Animal Husbandry Department, Agricultural Experiment Station, University of Puerto Rico, Rio Piedras 00928.