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Strategy to Limit Anthelmintic Resistance in Horses

Research from France and Switzerland showed that targeted deworming protocols can work on horse farms to reduce anthelmintic resistance.
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“A selective anthelmintic treatment scheme can be successfully implemented on riding horse farms with varying numbers of horses or horse owners," researchers said.

With no new anthelmintic drugs on the horizon, it is especially important to maximize efficacy of those currently available, particularly against cyathostomins (small strongyles). Over a six-year period, a field study evaluated a selective anthelmintic treatment course in 93 horses on five farms in France and Switzerland. [Roelfstra, L.; Quartier, M.; and Pfister, K. Preliminary Data from Six Years of Selective Anthelmintic Treatment on Five Horse Farms in France and Switzerland. Animals 2020, vol. 10, 2395; doi:10.3390/ani10122395].

Selective (also called targeted) deworming protocols rely on treatment based on fecal egg counts (FEC) to deworm only individuals with a FEC exceeding 200 eggs per gram (epg). Maintenance of a parasitic refugia with this strategy leaves susceptible worms unexposed to anthelmintics while also decreasing use of anthelmintic drugs within a herd. The less drug administered and the fewer parasites exposed, the less opportunity for helminths to develop resistance.

Fecal samples were collected twice (spring and fall) yearly for a total of 757 samples between autumn 2014 and spring 2020. Horse ages ranged between 3–32 years. Only 34.7% of these samples yielded EPG >200, targeting solely those horses for treatment with anthelmintics. This strategy ameliorates overuse of anthelmintic drugs that could stimulate parasitic resistance, and the study demonstrated that two-thirds of horses could potentially receive less intensive treatment than done in the past.

In conclusion, the authors stated: “A selective anthelmintic treatment scheme can be successfully implemented on riding horse farms with varying numbers of horses or horse owners, or under difficult management (e.g., frequent moving in/out of horses or horse owners) and pasture conditions.” 

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