Production benefit of treatment with a dual active oral formulation of derquantel-abamectin in slaughter lambs.

Gastrointestinal nematodes have a negative impact on the productivity of grazing sheep. Control of these infections has relied for decades on the use of anthelminics, leading to anthelmintic resistance (AR) worldwide, including the UK. The use of combination anthelmintics has been advocated as one of the tools in managing AR and decreasing the economic losses associated with AR. In this study, the benefit of a new combination (derquantel plus abamectin; DQL+ABA: Startect(®) Dual Active Oral Solution for Sheep, Zoetis, at 1 mL/5 kg bodyweight) was evaluated on a farm with suspected AR to benzimidazoles, by incorporating it into the existing treatment regime. In total 100 lambs were selected and allocated to one of two treatment groups, which were treated either with DQL+ABA or fenbendazole/levamisole at monthly intervals. All lambs were co-grazing the same pasture. Weight gain and carcass quality was evaluated, as well as treatment efficacy. The efficacy of DQL+ABA was high throughout the grazing season, whereas the efficacy of the fenbendazole/levamisole treatment regime was below the threshold for anthelmintic efficacy. The high efficacy of a monthly treatment with DQL+ABA resulted in a significantly higher average daily weight gain and shorter time to reach slaughter.