The integration of grazing management and summer treatments for the control of trichostrongylid infections in Merino weaners

Objective To compare two strategies for the preparation of pastures that have reduced trichostrongylid infections during winter and spring for Merino weaners. Design A replicated field experiment was conducted over two successive years. A ‘standard’ strategy, comprising set‐stocked wethers given anthelmintic treatments in late October and early February, was compared with a ‘new’ one in which intensive grazing for 1 month after each treatment and destocking for 1 or 2 months was integrated with the anthelmintic treatments. Paddocks prepared according to these strategies were set‐stocked at 15 Merino weaners/ha from April to October inclusively. Results Contamination of pastures prepared according to the new strategy was substantially reduced compared to those of the standard strategy. Worm counts showed that on new strategy paddocks the numbers of trichostrongylid larvae, except Nematodirus spp, were reduced by 50 to 95% compared to standard strategy paddocks. Worm egg counts from the set‐stocked weaners were reduced by about 50% on new strategy paddocks from April to October. Weaners grazing the new strategy paddocks grew significantly more clean wool (254 g, P=0.01) and were significantly heavier in October (3.2 kg, P = 0.01) than weaners in the standard strategy paddocks. The improved production was attributable partially to better pasture growth early in winter and partially to reduced parasitism. Conclusion The new strategy is a simple, practical and widely applicable example of the integration of grazing management with strategically timed anthelmintic treatments to reliably reduce trichostrongylid infections in weaners grazing during winter and spring.