Preliminary survey of anthelmintic efficacy in selected smallholder sheep and goat flocks in Sarawak, Malaysia

Smallholder sheep and goat production supports rural livelihoods and food security through the provision of meat, milk, hides and skins, employment, and household income in Malaysia. The control of gastrointestinal nematodes (GINs) in sheep and goats relies on routine deworming using albendazole, levamisole, and ivermectin anthelmintics. While these drugs are effective in reducing worm burden and improving animal productivity, prolonged and often indiscriminate use resulted in the emergence of anthelmintic resistance (AHR) in West Malaysia. Despite extensive evidence of AHR in GINs of sheep and goats in various production systems in Peninsular Malaysia, there is a significant knowledge gap regarding the status of anthelmintic efficacy of albendazole and ivermectin in GINs of sheep and goats in Sarawak. In this study, a preliminary experimental trial was conducted to evaluate the in vivo efficacy of albendazole and ivermectin using faecal egg count reduction test (FECRT) based on pre-treatment and post-treatment faecal egg counts conducted 14 days apart according to the updated World Association for the Advancement of Veterinary Parasitology (W.A.A.V.P) guidelines for diagnosing AHR in ruminants. Coprocultures were also prepared from faecal samples collected post treatment to microscopically identify the third stage larvae (L3) of resistant nematodes using standard morphological criteria. The results of FECRT on albendazole showed a 76.8% (90% CI: 69.9-83.8) reduction in pretreatment epg in White dorper sheep (Group D) while ivermectin treatment showed 85.4% (90% CI: 80.8-89.9) in Barbados blackbelly sheep (Group A), 75.8% (90% CI: 65.3-86.3) in White dorper sheep (Group C), and 75.9% (90% CI: 65.7-86.1) in Saanen goats (Group B). Thus, all the treatment groups did not achieve the W.A.A.V.P recommended post treatment FECR for susceptibility (lower 90% CI ≥ 90% and upper 90% CI ≥ 99%) in sheep and goats, which has led us to reject the null hypothesis and conclude anthelmintic failure in GINs of sheep and goats in Sarawak. This study provides the first evidence of anthelmintic failure involving albendazole and ivermectin in sheep and goat farms in Sarawak. Further study using adjusted dose regime is required to clarify the status of ivermectin resistance in goats because metabolic factors rather than resistance may precipitate a lower efficacy when using standard sheep dose in goats. Nonetheless, this work provides preliminary data that lays a solid foundation for designing sustainable helminth control programs to overcome anthelmintic resistance in Sarawak.