Effects of mineral supplementation on the performance of steers grazing birdwood grass (Cenchrus setiger) pastures in north Western Australia

The liveweight of Shorthorn steers on fertilized birdwood grass (Cenchrus setiger) pastures, growing on sandy 'Pindan' soils, at Derby, north Western Australia, was recorded over 3 years from September 1973 to July 1976. A separate draft of steers was used in each of the 3 years. Half of the steers in each draft were given a supplement of urea, phosphoric acid and ammonium sulphate in the drinking water. These supplemented steers gained an average of 147 kg, 128 kg and 93 kg per head, or 31 kg, 70 kg and 44 kg per head more, than unsupplemented steers in the 3 years. There was a consistent positive response in liveweight gains in all post-wet and pre-wet season periods, and a positive response in two of the three wet seasons. Two levels of pasture use were also imposed but did not have any consistent effect on pasture composition or liveweight gain. Copper injections, and cobalt as cobalt oxide bullets, were given to approximately half the stock in years 1 and 2 respectively. There was a small response (P < 0.05) to copper during the post-wet season, but over the whole grazing period the response was negligible. The cobalt bullets had no effect.