Integrated parasite management for sheep reduces the effects of gastrointestinal nematodes on the Northern Tablelands of New South Wales

Abstract

An experiment was conducted over 2 years on six commercial farms to quantify the costs of gastrointestinal nematode parasitism on grazing Merino ewes on the Northern Tablelands of New South Wales. To determine the effect of worm management practices, three farms implemented integrated parasite management (IPM) strategies and three farms continued to implement regionally typical industry practice (TYP). On each farm, 120 ewes born in 2006 and 120 mature age ewes were selected at shearing in 2007. Of these, 60 in each flock were serially treated with anthelmintics (CAP treatment) to suppress worm populations and the other 60 ewes were managed according to their respective farm management strategies (NOCAP treatment). Among NOCAP ewes, worm egg counts were significantly reduced over both years by IPM compared with TYP despite IPM farms requiring fewer anthelmintic treatments (3.5 vs 4.5 per year). In Year 1, mortality of sheep because of worms (CAP vs NOCAP) was significant on TYP farms (10.5%, P < 0.01) but was not apparent on IPM farms. Throughout the study, NOCAP ewes had significantly lower growth rates (–2.8 ± 0.1 kg/year, P < 0.01), produced less greasy wool (–170 ± 20 g, P < 0.01) and had reduced fibre diameter (–0.28 ± 0.05 μm, P < 0.01) when compared with CAP ewes. These effects were apparent for both TYP and IPM management. The results confirm the significant production loss caused by worms in a northern, summer rainfall region and show that IPM reduces the effect of worms and frequency of anthelmintic treatment compared with typical methods currently used by the industry.