Abstract:
Animal Production in Australia EFFECT OF EARLY STORMS ON THE DIET SELECTED BY GRAZING CATTLE A. ROMERO V.* and R.M. MURRAY* Efforts at overcoming the nutrient limitations of mature tropical pastures in north Australia have relied heavily on supplementary feeding of non-protein nitrogen (Winks and Laing 1972). Early storms during an experiment designed to examine supplementation of dry season pastures with urea, presented an opportunity to observe changes in the diet selected by cattle immediately before and after the break in the season. Four 3-year-old Droughtmaster steers with fistulae in the oesophagus and rumen grazing native pastures, were observed at CSIRO 'Lansdown' Research Station Townsville. The experiment, consisting of four periods each of three weeks, was commenced in September 1976. Data are presented for two animals during each period, one untreated and one which received 50 g urea + 10 g Na2S04 per day as an aqueous drench. Rain (33 mm) fell between the second and third period. The diets selected by the animals before and after this rain are shown in Table 1. Ammonia-N in rumen fluid rose from 40 mg/l prior to the rain, to 70 mg/l afterwards. The rain which fell during this experiment was enough to grow pasture of sufficient-quality to negate the effects of the urea supplement. Meteorological data from the research station indicate a 49% probability that 25 mm or more of rain could occur during October-November (R-L. McCown personal communication). This probability is high enough to convince many cattlemen to accept the risk of delaying feeding until October. However, by this time both pasture quality and cattle condition have deteriorated to such extent that little response is experienced to non-protein nitrogen supplements alone (S.R. McLennan personal communication). More research is required into the most appropriate supplement for feeding at the end of the dry season. WINKS, L. and LAING, A.R. (1972). Proc. Aust, Soc. Anim. Prod. = 9: 253. * Department of Tropical Veterinary Science, James Cook University, Townsville, Qld 4811. 465