A study of Merino sheep grazing a cotton-bush (Kochia aphylla)–grassland (Stipa variabilis–Danthonia caespitosa) community on the riverine plain

Abstract

A study was made of Merino sheep continuously grazing a cotton-bush (Kochia aphylla R.Br.)–grassland (Stipa variabilis Hughes–Danthonia caespitosa Gaudich.) community over a 2 year period. Observations were carried out at two stocking rates (0.75 and 0.375 sheeplacre) and comparisons were made with plots from which K. aphylla had been mechanically removed. The aim of the study was to define the contribution made by K. aphylla (a drought-resistant chenopodiaceous shrub) to animal production and to examine the effects of the seasonal variation in composition, availability, and food value of the pasture on animal behaviour and performance.

At the low rate of stocking K. aphylla contributed little to the diet of the sheep (max. 2% in autumn) despite its being at no time less than 20% of the forage available. At the high stocking rate its maximum contribution to the diet was 7% in late autumn.

The major constituents of the diet in spring were the annuals Hedypnois rhagadioloides (L.) Willd. and Hypochoeris spp. and in summer the perennials Danthonia caespitosa and Kochia pentagona R.H. Anderson. D. caespitosa was also the main component during autumn at the low stocking rate but at the high stocking rate it was replaced in the diet by a high proportion of dead matter and Medicago burr.

Seasonal variations in wool growth were greater at the high stocking rate than at the low rate, the lowest production occurring in autumn. Body weight and wool growth were not significantly altered by the presence of K. aphylla at either of the stocking rates.

The lowest recorded value for dietary crude protein was 8.8%. Wool growth was closely related to the in vitro digestibility of the forage eaten and to the availability of green feed within the pasture.