The comparative efficacy of four anthelmintics against a natural acquired Fasciola hepatica infection in hill sheep flock in the west of Ireland

The aim of this study was to evaluate the efficacy of four different anthelmintics against F. hepatica in a naturally infected hill sheep flock in the west of Ireland. In a randomised trial, 138 ewes were divided into four groups. On day 0 each group was dosed with one of four anthelmintics: triclabendazole, closantel, oxyclozanide or nitroxynil. Faecal samples were obtained from each animal per rectum on the day of treatment and again at 7, 14, 21 and 56 days post-treatment. The number of F. hepatica eggs per gram of faeces was determined using the sedimentation technique and the efficacy of each anthelmintic was calculated in terms of the percentage reduction in egg count at each time point. The results for closantel, oxyclozanide and nitroxynil indicate that these drugs are effective with faecal egg count being reduced by 100% by day 14 post-treatment. However, the results for triclabendazole group yielded lower efficacy levels, with faecal egg count reductions of between 49% and 66% based on arithmetic means, over the period 7–56 days post-treatment. These results are highly indicative of triclabendazole resistant F. hepatica in sheep on this farm.