Evaluation of lambs subjected to a targeted selective treatment anthelmintic regime

Targeted selective anthelmintic treatments (TSTs) can identify individuals less reliant on anthelmintic, information from which could be utilised to select lambs based on anthelmintic requirement. However, it is important to first determine if selection based on anthelmintic requirement compromises genetic potential for productive traits. Sheep Improvement Limited (SIL) estimated breeding values (eBVs) for production traits and associated indexes for 214 female lambs and 158 male Coopworth lambs were compared with their requirement for anthelmintic following exposure to a liveweight gain-based TST regime. Mean liveweight gain for both sexes was reduced with increasing anthelmintic requirement (P <0.001). Favourable increases in eBVs with decreasing anthelmintic requirement were observed for fecundity in both sexes (P = 0.003) and for survival in females only (P = 0.03). No effect was observed for eBVs for maternal survival, weaning weight, maternal weaning weight, live weight at eight months of age, and live weight and fleece weight at 12-months of age (P >0.05 for all). Dual purpose index values for resilience increased with decreasing anthelmintic requirement (P <0.001) while meat yield index and overall productivity were not affected (P >0.05 for both). It is concluded that selection of lambs for low anthelmintic requirement can be made with no apparent compromise in the genetic potential for production traits.