Field Efficacy Evaluation of Commonly Used Anthelmintics Against Gastrointestinal Nematodes on Naturally Infected Horses in and around Tulu Awuliya Town, North East Ethiopia

Gastrointestinal nematode (GIN) infections are major constraints to horse productivity, with effective control relying largely on routine use of anthelmintic drugs. However, the emergence of anthelmintic resistance threatens the long term sustainability of this strategy. Therefore, a field-based experiment was conducted from November 2020 to May 2021 in and around Tullu-Awliya town of South Wollo Zone to evaluate the efficacy of commonly used anthelmintics against GINs in naturally infected horses and to assess the control practices of horse owners. Fecal samples from 520 randomly selected horses were examined using flotation and modified McMaster techniques. Horses with fecal egg counts (EPG ≥ 150) were assigned into six groups of ten, representing cart and pack horses. Four groups received either Ivermectin or Fenbendazole, while two served as untreated controls. Fecal samples collected on day 0 and day 14 were subjected to fecal egg count reduction tests (FECRT) to determine anthelmintic efficacy. Copro culture and modified Baermann techniques were used to identify L3 larvae associated with suspected resistance. Egg reappearance period (ERP) was also conducted to detect anthelmintic efficacy in packing horses. Additionally, a questionnaire survey involving 201 horse owners documented helminth control and anthelmintic use practices. The FECRT results showed mean fecal egg count reductions of 94.01% for Ivermectin and 99.6% for Fenbendazole, with significant differences between treated and control groups. Ivermectin exhibited suspected resistance, and Strongylus vulgaris, Strongylus equinus, and Cyathostomum spp. were identified post treatment of Ivermectin. Moreover, ERP results suggested no anthelmintic resistance in pack horses. The survey indicated that Ivermectin 62.3%, followed by Fenbendazole 31.8%, were the most widely used anthelmintics. These findings highlight the need for improved awareness of rational anthelmintic use and adoption of resistance‑management strategies, alongside further studies on factors contributing to reduced drug efficacy.