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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.

During late summer, Border Leicester wethers running with Merinos on a pure Atriplex nummularia stand turned over 10.6 to 17.5 litres (mean 13.7 litres) of water daily, and diluted the sodium and potassium ingested to less than 1000 m-osmoles/litre in the urine. Leicesters used 46% more water than Merinos as litres/24 hr, and 71% more as ml/kg0.82/24 hr. The two breeds produced similar urine concentrations. The sheep showed a wide variation in response, and their individual water turnovers while feeding on Atriplex vesicaria and A. nummularia ranged from 120 to 833 ml/kg0.82/24 hr. This suggests differences in functional types of adjustment to saltbush associations. On a Danthonia community Leicesters again turned over more water than Merinos but only about half as much water was required as on saltbush. Merinos grazing on A. vesicaria (with some grasses available) over 2 years maintained good condition with half the water intake of Merinos on A. nummularia, although the two species of saltbush had similar sodium and potassium contents. Total body water tended to increase with water turnover rate on saltbush. Plasma sodium concentration was inversely related to water turnover, extracellular volume, and total body water on saltbush pastures. The content of extracellular sodium was, however, greatest in the sheep with the least sodium in the food taken.

A study was made of Merino sheep grazing a bladder saltbush (Atriplex vesicaria Hew. ex Benth.)–cotton-bush (Kochia aphylla R.Br.) community set stocked at three stocking rates (2.5, 1 .2, and 0.6 sheep/hectare) over a 3-year period. In spring the sheep preferred the perennial grass Danthonia caespitosa Gaudich. and the annuals Medicago polymorpha L. and Vulpia myuros (L.) K. C. Gmel. to the more abundant A. vesicaria. From summer to early winter the diet consisted mainly of A. vesicaria with the proportion of dead matter and Medicago burr increasing as the availability of A. vesicaria decreased. Seasonal fluctuations in wool growth were evident at all three stocking rates. Maximum wool growth rates occurred in spring when the nitrogen content (2.3%) and in vitro digestibility (65%) of the forage eaten was high. During autumn and early winter values for nitrogen (1.4%) and digestibility (50%) were lower and wool growth was at a minimum. At 0.6 sheep/ha animal productivity was maintained and there was little decline in the A. vesicaria population during the 3 years. Grazing eliminated all the A. vesicaria from the pasture stocked at 2.5 sheep/ha, and 98% at 1.2 sheep/ha. At these higher stocking rates the pasture proved incapable of maintaining the sheep for the 3-year period. The inability of A. vesicaria to recover after heavy or complete defoliation by grazing demonstrates the necessity of adopting a low stocking rate if the bush is to be retained.

To determine the response of the perennial shrub Atriplex vesicaria Hew. ex Benth. (bladder saltbush) to grazing, bushes were grazed by Merino sheep to two levels of defoliation, severe and complete. Ungrazed bushes were used as controls. Separate groups of plots were defoliated in October and February and two levels of soil moisture were imposed. Results showed that the more heavily the bushes were grazed the less likely they were to regenerate. Completely defoliated bushes did not regrow, irrespective of soil moisture status or season. It is hypothesized that the inability of A, vesicaria to persist after complete or severe grazing is due to the removal, by grazing, of potential growth sites which apparently occur only along the young stems.