Cattle and sheep production on an Atriplex vesicaria (Saltbush) community

Abstract

A comparison was made between the productivity of sheep and cattle grazing on a semiarid saltbush (Atriplex vesicaria Heward) community (median annual rainfall 303 mm) over a 4 year period. Hereford cattle were grazed at 11.7 and 17.5 ha/cow and Merino sheep were grazed at 1.7 and 2.5 ha/ewe. The cows and ewes were joined annually so that they calved and lambed in the May- June period. Calves were weaned at 7-8 months, and the lambs were weaned at c. 4 months. Both calves and lambs were then retained on separate plots for a further 12 months. The saltbush community consisted of a low shrub layer containing 250-750 kg A. vesicaria forage per ha and a herbage layer containing 25-650 kg of forage per ha. Despite the higher digestibility and nitrogen content of the sheep diets, the sheep and cattle had similar productivity. The production of body weight to weaning was a mean of 10.6 and 15.1 kg/ha/year (low and high stocking rates) for the cattle and a mean of 9.4 and 13.2 kg/ha/year for the sheep. After correction for metabolic mass (kg0.9/ha), the body weight production of sheep was raised to 12.4 and 17.3 kg/ha/year. At 12 months after weaning, the equivalent values were 12.9 and 19.4 kg/ha for cattle, and 13.4 and 20.1 kg/ha (corrected) for sheep. Thus differences are small and arise from the stocking rate chosen rather than from biological differences in productivity. There was no relative change between sheep and cattle in body weight growth between good and moderately poor seasons. The livestock numbers for equivalence of grazing pressure were calculated as 9.2 sheep to 1 cattle. The cattle drank an average of 46,300 litres of water each in a year, while sheep drank only 3300 litres per year. On this basis the water supply for cattle grazing would need to be 50% greater than for sheep grazing on the same saltbush land. In addition to body growth, the sheep produced 1.4-2.0 kg clean wool per ha, which provides a substantial economic advantage for sheep in these lands.