Effect of anthelmintic dosing and stocking rate on the productivity of weaner sheep in a Mediterranean climate environment

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Abstract
The effects of nematodiasis on productivity in weaner sheep was measured at Kybybolite Research Centre, South Australia, during 1976-81. Three levels of control were compared at two stocking rates (7.5 ha-1 and 16 ha-1). One group was not treated with anthelmintics, another group was treated every 3 weeks and the third group (Planned) was given five doses of anthelmintics each year: once in October, twice during the hot dry summer and twice during the winter months. The sheep were replaced by weaner sheep at shearing in October each year. The drenching regime of sheep on a particular paddock was the same for all five years. Nematodes, particularly Trichostrongylus spp., had a very large effect on the production of the sheep. The mean annual death rate of the untreated sheep was 22% and 56070, for the low and high stocking rates respectively. The regularly drenched sheep were 9-31% heavier and cut 11-46% more wool than the survivors of the untreated sheep at the low stocking rate. At the high stocking rate the regularly drenched sheep were 17-58% heavier and cut 14-56% more wool than the survivors of the undrenched sheep. The sheep given the Planned drenching program had similar final liveweights each year to the regularly drenched sheep, and in only two years out of five did the regularly drenched sheep produce significantly more wool than the sheep given the Planned program. The effect of drenching on the contamination of wool with faeces, and the resultant effect on the incidence of fly strike, is discussed. There was a significant variation between years in amount of available pasture, and there was generally slightly more pasture available on the Nil drench treatment paddocks.