Botanical and chemical composition of the diet selected by cattle in three range types in central Australia.

Abstract

The diet selected by oesophageally fistulatcd cattle was assessed for its botanical and chemical composition in three range types, Acacia (mulga) Shrublands, Open Woodlands and Astrebla (Mitchell grass) Grasslands, in central Australia. The study was conducted over a 15 month period commencing in September, 1976 during a period of above-average rainfall. There were few positive correlations between range condition, as assessed by the now superceded STARC method, and attributes such as forage biomass, dietary nitrogen or in vifro digestibility values. Cattle had a larger than usual biomass of forage to choose from and a greater species richness because of seasonal conditions. Cattle preferred annual grasses and forbs to the perennial species in the three range types except that browse species made up a large proportion of the diet after the flush of annuals had gone. Levels of dietary nitrogen were generally higher in Acacia Shrubland than in Open Woodland and Astrebla Grassland, were related to rainfall rather than seasons and dropped below maintenance level when forage dried off, even during the favourable climatic conditions of the study. Selection of some forage species was intense and the long term impact of grazing on these species is likely to lead to their further decline. Graziers must consider the condition and availability of forage species in addition to cattle behaviour and condition when making management decisions.