Efficacy of moxidectin against cyathostomins after long-term use in a large herd of draught horses with a high stocking density.

This scientific study explores whether a large group of draught horses, which had been consistently treated with the drug moxidectin over a five-year period, developed resistance to the medication. The research showed no evidence of resistance, despite initial reductions in parasite egg counts in the faeces of these horses post-treatment which were not maintained.

Objective of the Study

• The key aim of this research was to determine if resistance to the drug moxidectin had developed in a large herd of draught horses. These horses had been routinely treated with moxidectin for a span of five years.

Methods and Approach

• In conducting their study, the researchers collected faeces of the horses for egg counts just before orally administering moxidectin gel to the horses.
• This faecal sampling and testing were repeated at specific intervals: seven, 30, 60, and 90 days post-treatment.

Results of the Study

• The findings revealed a significant decrease in faecal egg counts at the seven and 30-day marks following treatment with moxidectin.
• However, the egg counts observed at the 60 and 90-day marks post-treatment showed no significant difference from the counts recorded before moxidectin treatment was administered.

Conclusion

• The results indicate no clear evidence of resistance developing in these horses against moxidectin, despite the initial post-treatment reductions in faecal egg counts not being maintained in the longer term.
• Therefore, in the examined group of draught horses consistently treated over a long-term period with moxidectin, parasite resistance to the drug did not clearly manifest.