Comparisons of the productivity of sheep grazing natural pastures of the Riverine Plain

Abstract

The productivity of Merino sheep grazing on the semi-arid natural shrub (Atriplex vesicaria) and grassland (Danthonia caespitosa-Stipa variabilis, D. caespitosa, S. variabilis) pastures of the Riverine Plain was measured over three years. At 0.5 sheep to an acre, the sheep on A. vesicaria (bladder saltbush) community at first grew more wool than those on the grasslands, but wool growth rate declined in autumn to the same degree as on the grassland. In the second year most of the A. vesicaria bushes did not recover from grazing and wool growth-rate fell to half that on the grasslands. The sheep on A. vesicaria had to be removed in the second year, but on the grasslands there was no evidence that sheep could not be maintained indefinitely at that stocking rate. At 1.0 sheep to an acre, both the A. vesicaria and the D. caespitosa-S. variabilis grassland were incapable of maintaining the sheep for the duration of the experiment. Wool growth of the sheep on the grasslands showed an annual rhythm, with high growth-rate in spring (14 g per day) followed by a gradual decline in rate to 6-8 g per day in late summer and autumn. However, the extent of this decline was dependent on summer rainfall, as in one summer when rainfall was high, wool growth-rate was maintained at near the spring rate. The mean annual rate of wool growth was found to be correlated (r = + 0.92, P<0.01) to summer rainfall (November-April). The weight gain of weaner sheep was best on E. caespitosa, and was equaiied by that on A. vesicara only in the first year. Growth was not influenced by the presence or absence of bushes of Kochia aphylla Growth on S. variabilis was less than on D. caespitosa.