A Multi-Farm Assessment of Anthelmintic Efficacy Against Gastrointestinal Nematodes of Sheep and Goats in St. Kitts, West Indies

Anthelmintic resistance (AR) in gastrointestinal nematodes (GINs) is an increasing threat to the health and productivity of small ruminants, but contemporary information on the efficacy of commonly used anthelmintics in sheep and goats in St. Kitts is limited. This study evaluated the efficacy of selected anthelmintic treatments against GINs in naturally infected sheep and goats from smallholder farms in St. Kitts using the fecal egg count reduction test (FECRT), complemented by coproculture to characterize the nematode genera present before and after treatment. Because flock sizes were generally small and insufficient, numbers of eligible animals were not available within individual farms to establish adequately sized groups for all treatments. Hence, the anthelmintics were evaluated in separate treatment groups across selected farms rather than concurrently within individual flocks. Anthelmintic efficacy was assessed using FERCT estimates and 90% confidence intervals, with resistance interpreted according to established criteria. In goats, reduced efficacy consistent with resistance was observed in the albendazole, moxidectin, and ivermectin treatment groups using both analytical approaches. The response to levamisole was borderline or inconclusive because its classification differed between the analytical methods, whereas monepantel and derquantel–abamectin showed high efficacy. In sheep, reduced efficacy consistent with resistance was observed in the fenbendazole, moxidectin, and ivermectin treatment groups, whereas levamisole, monepantel, and derquantel–abamectin showed high efficacy. Haemonchus predominated in pre- and post-treatment larval cultures; however, the pooled nature of the coproculture data precluded definitive attribution of resistance to individual nematode genera. In goats, resistance was detected to albendazole, moxidectin and ivermectin, while levamisole showed borderline efficacy, with classification differing between the analytical methods used. Monepantel and the derquantel–abamectin combination remained effective. These findings provide evidence of reduced anthelmintic efficacy in several treatment groups evaluated, rather than demonstrating widespread multidrug resistance across sheep and goat populations in St. Kitts. They highlight the need for continued, appropriately designed surveillance of anthelmintic efficacy to support evidence-based and sustainable gastrointestinal nematode control in small ruminants in St. Kitts.