Seasonal variations of nitrogen and digestible energy intake of cattle on tropical pasture

Abstract

Organic matter intake of cattle grazing tropical pastures was measured during periods of, firstly, new grass growth in the wet season, secondly, regrowth of grass pasture following rain, and thirdly, mature growth consisting of chiefly either grass or legume. The measurements were made by reference to digesta markers on fistulated cattle carrying portable equipment. The intake values of digestible energy were considered in relation to digestibility values obtained from diet samples from oesophageally fistulated cattle grazing grass and legume pastures over a 5-month period, and also to changes in liveweight of a group of unfistulated cattle grazing the same pastures. The measured values of digestible energy intake during new pasture growth, regrowth and during the dry season were in accord with the weight changes. The relationship between digestibility and liveweight change suggested that the primary limitation to the growth of cattle on tropical pastures is one of digestibility. Although supplementary nitrogen is known to increase feed intake in deficient situations, it would seem that substantial improvement of dry season nutrition can only be achieved by using forage that is more digestible than the native vegetation. Some legume introductions appear to do this.