Anthelmintic use and resistance on thoroughbred training yards in the UK.

This research study investigates the use and resistance to deworming drugs (anthelmintics) on thoroughbred horse training yards in the UK, focusing on issues relating to the growing resistance of these drugs among parasitic worms (nematodes).

Study Methodology

• The research reached out to 157 horse training yards, and 106 voluntarily participated in the study. Out of these, 64 were visited in person, while the rest were contacted via telephone and post.
• During these interactions, questionnaires were answered, and containers for faecal samples handed out. The samples were collected from the horses on the day of the treatment, as well as a week or more afterwards, depending on which drug (pyrantel, fenbendazole, ivermectin or moxidectin) was used.
• The researchers assessed the collected faecal samples using the modified McMaster technique to find out how many eggs were present in the faeces.
• They also used a technique called the microagar larval development test (MALDT) to see whether the worms were resistant to the medications used to deworm the horses.

Key Findings

• Only 16% of the horses had positive egg counts at the time of treatment. This indicates that many of the treated horses might not have needed treatment at all.
• Of the yards studied, only 39% were removing faeces at least weekly, and only one-third were doing so two or more times a week. This could be contributing to the spread of resistant worms.
• Majority of the yards (82%) treated new arrivals with their standard worm prevention routine, with the use of moxidectin being the most popular.
• Most of the yards selected the medications used based on veterinary advice (34%), their own decision (31%), or the need to rotate between products (33%).
• Faecal egg counts, a key indicator of worm infestation, were rarely used, with 51% of the yards never using them, and 32% only using them if a horse was visibly unwell.

Implications and Conclusions

• This study suggests that there may be overuse of deworming drugs on some yards. This overuse can lead to increased resistance among parasitic worms to these medications, rendering them less effective over time.
• The study also reveals the need for more regular and systematic monitoring of worm infestations (like faecal egg counts) and the removal of faeces, for more effective management of worm infestations in horse yards.