Effect of Grazing System and Anthelmentic Treatment of Ewes on Parasitic Challenge and Lamb Growth.

Abstract

The adverse effect of parasites on lamb growth rate has been well documented. The combination of concerns about worm resistance to anthelmintics and consumer demand for products without chemical residues has increased the need to re-evaluate current control methods. In order to be effective and sustainable, control measures should include grazing management systems that exploit parasite life cycles. This will facilitate the rational use of anthelmintics. The work undertaken, over three grazing seasons, was designed to evaluate the effect of a “safe” grazing system on the gastrointestinal parasite (roundworms) levels in ewes and lambs, on the number of infective larvae on herbage and on lamb growth. The study comprised 6 similar sized paddocks; 2 paddocks of permanently grazed sheep pasture (“contaminated”) and 4 paddocks of which 2 were rested from lambs in alternate years to render them safe for lambs (“safe”). Ewes and lambs were set stocked on 2 “safe” and 2 “contaminated” paddocks each year. The first year was treated as an establishment year for the study. The main results confirm the merits of not grazing ewes and their lambs on the same pasture from lambing to weaning in successive years in achieving lower numbers of infective Nematodirus larvae on pasture, which ultimately translates as “safer” levels in lambs. There was a low level of residual over-wintered infection of “other trichostrongyles” on pasture in spring and this most likely could be attributed to the dosing regime used in the study which served to reduce contamination on pastures in late summer / autumn period.