The reappearance of strongyle eggs in the faeces of horses after treatment with moxidectin.

This research study looks at the differences between two medications, moxidectin and ivermectin, in preventing the recurrence of strongyle eggs in horse faeces post-treatment, with findings indicating a higher efficacy or longer residual effect of moxidectin.

Study Overview

• This study compared the recurrence of strongyle eggs in horse faeces following treatment with two medications, moxidectin and ivermectin. It was conducted over a six-month period between December 1995 and June 1996.
• The horses were naturally infected from a prior grazing period and split into two groups of 24 horses each, one group being treated with moxidectin and the other with ivermectin.
• The horses were housed from a week before the study until the 17th week of the study, after which they were put to pasture.
• There were no observed side effects from either treatment, and faecal samples were taken from each horse at specified points throughout the study for examination.

Findings

• The ivermectin treated group had to be retreated in week 17 due to an increase in strongyle eggs in the faeces. This was initially observed in week 8, with a gradual increase seen until week 15 when the numbers of eggs per gram of faeces reached a plateau.
• This ivermectin group was withdrawn from the study after week 17 due to the need for retreatment and preventing possible pasture contamination.
• In contrast, the group treated with moxidectin showed very low mean egg counts throughout the study, with a plateau reached in week 19 and egg counts ranging from 10 to 30 eggs per gram of faeces between weeks 19 and 25.

Implications

• The difference in egg outputs post-treatment between the two groups suggests that moxidectin might be more effective against mucosal stages of the strongyle infection, or that it may have a longer residual effect than ivermectin.
• This research highlights the importance of selecting an effective medication for treating strongyle infections in horses, considering not only immediate treatment but also the potential for recurrence and impacts on wider contamination risks.