A grazing study was conducted in a semi-arid mulga (Acacia aneura) woodland to determine the relative
importance of variables controlling sheep production in this environment. The study was based on six
sheep stocking rates (0.3-0.8 sheeplha) with the exclusion of other large herbivores including kangaroos
and feral goats. The availability of forage and its components, together with the wool growth and live
weight of the sheep were measured every three months for seven years from October 1986.
Annual rainfall accounted for 60% of the annual variation in live weight gain per head and 79% of the
variation in wool growth per head. Stocking rate accounted for an additional 10% of the variation.
Rainfall accounted for this large proportion of variation by its strong influence on the yield of green leaf
which accounted for 78% of the variation in live weight gain and 66% of the variation in wool growth.
Green leaf was a determinant of sheep production because of its superior crude protein content and
digestibility compared to dry leaf and stem.
The species comprising this green leaf had an influence on sheep production only during drier years
when the presence of palatable perennial grasses became important to sheep production. The frequency
and yield of perennial grasses were greatly diminished at high stocking rates. This change in forage
composition caused a decline in sheep productivity as detected by a loss of linearity in the relationship
between stocking rate and live weight gainlhead.
We conclude that adjusting stocking rates is required in this environment for maintenance of long-term
sheep productivity and landscape function. The loss of palatable perennial C, grasses over much of the
region has reduced livestock productivity and increased the variability in forage availability. Stock
numbers should be adjusted at critical times to avoid losing perennial grasses that are important for sheep
production in drier years. New grazing strategies are required to restore these grasses to the region.
Full-text publications from the Australian Rangelands Society (ARS) Biennial Conference Proceedings (1997-), Rangeland Journal (ARS/CSIRO; 1976-), plus videos and other resources about the rangelands of Australia.