The utilization of spear grass (Heteropogon contortus). IV. The nature and flow of digesta in cattle fed on spear grass alone and with protein or nitrogen or sulfur

Abstract

Digestion studies were carried out with steers fed on low quality spear grass (Heteropogon contortus) alone and supplemented with either urea and sulfur or cottonseed meal. Urea and sulfur were administered by continuous infusion and cottonseed meal by direct addition to the rumen once daily. Supplementation with either non-protein nitrogen or true protein resulted in a significant increase in digestible organic matter intake without any apparent change in the apparent digestibility of the diet. Digestible organic matter intakes were 1.48, 1.88 and 2.28 kg day for spear grass, spear grass plus urea and sulfur and spear grass plus cottonseed meal respectively. On all diets there was a net gain of nitrogen in the stomach, highlighting the role of recycled nitrogen in the digestion of low quality feedstuffs. Thirty-five g of non-amonia nitrogen per day (2.7 g/100 g organic matter digested in the stomach) reached the intestine when the diet was spear grass alone, 46 g (3.0 g/100 g dry organic matter) when the supplement was urea and 72 g (3.8 g/100 g) when the supplement was cottonseed meal. The result demonstrates the limitations of supplements of urea in improving the nitrogen status of animals fed on a basal diet of low quality (low energy) roughage.