The first report of triple anthelmintic resistance on a French Thoroughbred stud farm.

This research paper documents a triple anthelmintic resistance in strongylid nematodes found in a French Thoroughbred stud farm, marking the first known case of such strongylid resistance in France.

Research Context

• The research specifically focused on anthelmintic (AH) drugs, which are commonly used against parasitic worms (nematodes) that infest horses.
• Strongylid nematodes often plague thoroughbred horses and can cause severe health effects. The spread of these parasites is of concern, especially if they show resistance to commonly used AH drugs.
• Resistance to AH drugs can jeopardize horse health and performance, making it a significant issue for stud farms.

Methodology and Analysis

• The study was conducted over a 10 month period from March to December 2023 on a French galloping racehorse stud farm.
• The study incorporated three groups of horses: one group of 6 males, one of 13 females, and one mixed group of 8 females and 3 males. These groups were tested for resistance to the AH drugs fenbendazole, ivermectin, and pyrantel.
• The researchers utilized Faecal Egg Count Reduction Tests (FECRTs) in accordance with guidelines from The World Association for the Advancement of Veterinary Parasitology (WAAVP).
• The researchers assessed the efficacy of each drug by calculating the 90% confidence interval of the percentage faecal egg count reduction post-treatment.
• Fenbendazole was tested once, ivermectin was tested twice, and pyrantel was tested once during the study.

Results and Implications

• The research discovered a significant development: the first reported case of triple AH resistance in strongylids in France.
• The tests showed that the resistance was present against all three anthelmintic drugs—fenbendazole, pyrantel, and ivermectin—in all the groups where these drugs were tested.
• The precise number of animals in each tested group was satisfactory for maintaining ≥80% power for the resistance tests.
• This result is precedent-setting and highlights the urgent need for further research across a wider range of farms and horse species to understand the prevalence of AH resistance in France.
• Such studies are critical to refining practical and effective recommendations for equid owners to manage and prevent the spread of these drug-resistant parasites.