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Apparent and True Digestibility of Forage Nutrients by Ruminant Animals^{1, 2,}

Department of Animal Sciences, Rutgers—The State University, New Brunswick, New Jersey

ABSTRACT

Digestion trials were carried out on 17 forages (16 orchardgrass, 1 alfalfa) with growing Jersey steers. Digestible dry matter of orchardgrass first harvests declined at the rate of 0.4% unit for every day's delay in harvest from May 11 to June 3. Aftermath (40-day regrowth) was higher in digestible dry matter than 55-day regrowth intervals and later cut first harvests, but did not equal the May 11 first harvest. Aftermath harvests did not exhibit the sharp decline in DDM as did first harvests. Prediction of per cent digestible dry matter by chemical composition was best expressed by the equation Y = 59.2 – 2.75X₁ – 0.24X₂ + 0.66X₃ + 0.50X₄, where X₁, X₂, X₃, and X₄ represent per cent lignin, hemicellulose, crude protein, and cellulose, respectively. The coefficient of variation was 3% and the coefficient of correlation was 0.80. For differences in digestible dry matter, 64% of the variation was explained by lignin (40%), hemicellulose (16%), cellulose (4%), and crude protein (4%). The coefficient of true digestibility was larger for hemicellulose (81% average) than for cellulose (75% average), and these coefficients reflect the absence of the respective fecal endogenous fractions. Average true neutral detergent solubles digestibility was 90%. Average true protein digestibility, using two methods (with and without fibrous contribution), was 92 and 87%. The average recovery of ingested lignin from feces was 104% (CV of 17%).

¹ Paper of the Journal Series, New Jersey Agricultural Experiment Station.

² Data in this paper are from a thesis submitted by the senior author in partial fulfillment of the requirements for the degree of Doctor of Philosophy.

³ Present address: H. K. Webster Company, Lawrence, Massachusetts.