Nutritional value of Townsville stylo (Stylosanthes humilis) and of spear grass (Heteropogon contortus)-dominant pastures fed to sheep. 1. The effect of plant maturity

Abstract

The voluntary dry matter intake, digestibility and chemical composition of Townsville stylo and of black spear grass cut at different times of the year from a site near Townsville, Queensland, have been examined using penned sheep. Nitrogen, sulphur, and phosphorus intakes and retention in the sheep were measured. The concentrations of N, P, S, Na, and Ca in most cuts of spear grass and P and Na in Townsville stylo were less than the published requirements of animals. With spear grass, digestible dry matter intake declined rapidly from January to April and more slowly from April to October and by mid-March fell below the estimated energy requirements for maintenance of sheep. There was little change in digestible dry matter intake of Townsville stylo between February and May and the level was well above maintenance requirements. Dry matter intake and dry matter digestibility were linearly related but only about 50 per cent of variations in intake were caused by variations in digestibility. Nitrogen balance was linearly related to nitrogen intake, and sulphur balance was linearly related to sulphur intake. Phosphorus intakes were usually less than 1 g P day-l and animals were usually in negative P retention.