Effect of stocking rate, lambing time and pasture management on wool and lamb production on annual subterranean clover pasture

Abstract

Border Leicester x Merino ewes mated to Dorset Horn rams grazed subterranean clover and annual ryegrass pasture in a 2 x 2 x 4 factorial arrangement having two stocking rates (8.1 and 12.3 eweslha); two lambing times—winter (May, June, July), and spring (August, September); and four management systems, viz. set stocking (SS), autumn saving and spring hay cut (AS), replacement of half the pasture by oats or lucerne (ISP), and replacement of half the pasture by both oats and lucerne, a quarter each (2SP).

The percentage of lambs born to ewes mated was lowest from May lambing and progressively increased up to August–September lambing. However, although July lambing produced marginally fewer lambs with slower growth rates than August–September lambing, the difference was not significant and the extra time available with July lambing for lambs to reach a marketable liveweight before pasture senescence meant that the earlier lambing treatment actually produced more prime lambs.

The set stocking and autumn saving systems resulted in greater annual wool and lamb production than the substitute pasture systems. Any extra fodder available from oats or lucerne in those treatments failed to make up for losses in animal production associated with a reduction in available fodder during the crop preparation phase. Deterioration of annual pasture caused by plant losses associated with intermittent grazing may have reduced production further in substitute pasture treatments.

The results suggest that in southern Australia on annual subterranean clover pasture the optimum level of stocking and the pasture management strategy for prime lamb production can be assessed by a careful observation of the botanical succession taking place, especially if the pasture is continuously grazed.

The results also suggest that optimum fertility should be foregone in favour of an earlier lambing, in order to provide sufficient time before pasture senescence for lambs to reach a marketable liveweight. The optimum time for lambing for prime lamb production for a particular region will depend on the time of year when the pasture in the region normally matures.