In vitro digestibility and carbohydrate composition of Digitaria decumbens and Setaria anceps grown at different levels of nitrogenous fertilizer

Abstract

Two tropical pasture grasses, Digitaria decumbens cv. Pangola and Setaria anceps cv. Nandi, were compared on the basis of in vitro digestibility and carbohydrate composition. These species were grown at three different levels of applied nitrogen (280, 476, and 673 kg/ha) and continuously grazed at one stocking rate of 6.2 beasts per ha. The in vitro digestibility of both species apparently increased with applied nitrogen, Pangola being slightly superior at the higher nitrogen levels. Lignin did not appear to be a major factor influencing digestibility. Total extractable carbohydrates (ethanol + water-soluble) varied little with nitrogen level, although Pangola was consistently higher (c. 9.0 %) than Setaria (c. 7.2 %). Pangola had a higher total cell wall polysaccharide content than Setaria at all nitrogen levels. Numerical analysis showed a reduction in cell wall polysaccharides in both species with increasing nitrogen, this effect being more marked in Setaria. The concomitant liveweight gains showed an overall superiority in Pangola which accounted for c. 80 % of the variation in the system; a further 16% was attributable to the increased responsiveness of Setaria to applied nitrogen. Since the total cell wall polysaccharides were higher in Pangola than in Setaria, it appears that Pangola polysaccharides are more digestible than those of Setaria.