Comparison of a single dose of moxidectin and a five-day course of fenbendazole to reduce and suppress cyathostomin fecal egg counts in a herd of embryo transfer-recipient mares.

The study compared the efficacy of single-dose moxidectin and a five-day course of fenbendazole for reducing and suppressing cyathostomin fecal egg counts in a herd of embryo transfer-recipient mares. The outcome revealed that moxidectin outperformed fenbendazole in terms of reducing and suppressing the egg counts.

Research Methodology

• The experiment was conducted as a clinical trial with 120 mares from 21 states, all residing on a single farm.
• An initial fecal sample was collected from each mare; only those mares with a cyathostomin fecal egg count (FEC) of ≥ 200 eggs/g were assigned to treatment groups.
• 82 horses received either fenbendazole (10.0 mg/kg, PO, q 24 h for 5 days) or moxidectin (0.4 mg/kg, PO, once).
• FEC data were collected and compared 14, 45, and 90 days post-treatment.

Research Results

• 14 days post-treatment, moxidectin-treated mares experienced a mean FEC reduction of 99.9%, whereas fenbendazole-treated mares had a mean reduction of 41.9%.
• By the 45th day, the mean FEC of fenbendazole-treated mares exceeded pre-treatment counts. However, the FECs of moxidectin-treated mares remained below pretreatment values throughout the 90-day study.
• Significant statistical differences were found between the two treatment groups’ FECs at all data collection points: 14, 45, and 90 days post-treatment.

Study Conclusion

• The five-day regimen of fenbendazole failed to adequately reduce or suppress FEC, suggesting inadequate adulticidal and larvicidal effects.
• In contrast, a single dose of moxidectin effectively reduced and suppressed FEC for an extended period.
• Given the wide geographic distribution of the study mares, these results are likely representative of cyathostomin-infected mares across much of the United States.
• The study, therefore, confirmed previous research indicating that fenbendazole resistance in cyathostomins is widespread and that moxidectin remains an effective treatment for controlling these parasitic infections.