Controlled dose confirmation study of a 2% moxidectin equine gel against equine internal parasites in The Netherlands.

This research aimed to test the effectiveness of a 2% moxidectin equine gel in controlling internal parasites in horses. Conducted at Utrecht University, the study found the gel to demonstrate high efficacy (over 99%) in reducing faecal egg output, but it had a limited impact on some parasites and none on others.

Methodology

• The controlled trial involved twelve yearling castrated male Shetland ponies that were allowed to graze a pasture of 2 hectares from May until November 1994.
• Six of these ponies were treated with a gel containing 2% moxidectin at a dosage rate of 0.4 mg/kg, while the other six acted as untreated controls.
• Necropsy (animal autopsy) was conducted 35 days after treatment to investigate the effect of the medication on various internal parasites.

Results

• The treated ponies exhibited more than 99% efficacy of moxidectin based on the reduction in the output of faecal eggs, indicating successful removal of parasites.
• A significant reduction of almost 90% was noted in the numbers of large fourth stage larvae (L4) residing in the mucosa (inner lining) of the ponies’ intestines.
• However, the treatment did not have an effect on early cyathostome L3 (EL3) or on the total numbers of mucosal developing stages, suggesting these parasites are more resistant to moxidectin.
• Interestingly, the researchers noted that the moxidectin treatment seemed to initiate the development of EL3, but the reason for this was not explained in the abstract.
• Furthermore, the medication was highly effective (95-100%) on lumenal L4 cyathostomes, adult strongylids, Strongylus vulgaris larvae from the arteries, S. edentatus larvae from the abdominal wall, and Trichostrongylus axei.
• On the contrary, the treatment had relatively poor efficacy against Gasterophilus intestinalis and absolutely no effect on Anoplocephala perfoliata.
• No side-effects from the use of the moxidectin treatment were observed.

Conclusion

• The study illustrates the potential of 2% moxidectin equine gel in controlling some equine internal parasites but it also highlights its limitations, as it had poor or no effect on certain parasites.
• Further research is necessary to understand why moxidectin does not affect certain parasites and the reason behind its initiation of EL3 development.