A study to evaluate the field efficacy of ivermectin, fenbendazole and pyrantel pamoate, with preliminary observations on the efficacy of doramectin, as anthelmintics in horses.

The research looked at how effective various drugs were in treating worm infections in horses, with the specifics of the study conducted in South Africa’s Free State Province. The test was conducted on 50 horses across two different locations to better understand the effectiveness of drugs such as Ivermectin, Fenbendazole, Pyrantel pamoate, and Doramectin in the field.

Study Design and Methodology

• The study involved 50 horses, 25 at each study site, in South Africa’s Free State Province. These horses were equally divided into five different groups. Four groups each received a different treatment while the fifth was the control group.
• The treatments administered to the horses were Ivermectin, Fenbendazole, Pyrantel pamoate, and Doramectin. The first three were orally administered at doses of 0.2 mg/kg, 10 mg/kg, and 19 mg/kg respectively while Doramectin was administered by intramuscular injection at a dosage of 0.2 mg/kg.
• The effectiveness of the treatments was determined by comparing the mean reduction in faecal egg count, 14 days post-treatment.

Results and Observations

• The study showed that Ivermectin, Fenbendazole, and Doramectin resulted in 100% reduction of faecal egg counts at Site A. Pyrantel pamoate was slightly less effective with a reduction of 96.1%.
• At Site B, only Ivermectin and Doramectin resulted in a 100% reduction. Fenbendazole’s effectiveness reduced with an 80.8% reduction while Pyrantel pamoate resulted in a 94.1% reduction.
• Interestingly, the study also found that Doramectin led to a 100% reduction in faecal egg counts at both sites, this was significant as Doramectin is not officially registered for use in horses, suggesting potential new usage.
• In addition, a reduced efficacy of Fenbendazole was observed at Site B, suggesting potential resistance to benzimidazole, the class of drugs that Fenbendazole belongs to.

Parasites identified

• The study also identified the species of parasites affecting the horses. Larval cultures showed that cyathostomes were the major infesting organism, accounting for up to 86% and 96% of the pre-treatment burdens at both sites.
• Other parasite species identified in the horses’ faecal samples included Strongylus spp. and Trichostrongylus axei.