New veterinary guidelines: The latest in equine parasite control
> Large strongyles are now rare, and cyathostomins (small strongyles) are now the major parasite of concern in adult horses. Parascaris equorum is still considered the primary parasite infecting foals and weanlings.
> Anthelmintic resistance is highly prevalent in cyathostomins and P. equorum and should be factored into treatment regimens.> Adult horses vary greatly in their innate susceptibility to cyathostomin infection and level of strongyle egg shedding and thus require individualized control programs.
> Horses younger than 3 years old require special attention as they are more susceptible to parasitic infection and are at greater risk of developing disease.
Because decades of frequent anthelmintic use have selected for high levels of anthelmintic drug resistance in cyathostomin and P. equorum populations, formerly popular control methodologies are not sustainable and new strategies are needed.
As for the frequency of treatment, less is more, says subcommittee member Ray Kaplan, DVM, PhD, DACVM, DEVPC, professor at the University of Georgia College of Veterinary Medicine. "Frequent treatments are unnecessary and often counterproductive," he explains. Instead, veterinarians need to emphasize properly timed treatments with effective anthelmintics administered at the appropriate time of the year—i.e. during epidemiological transmission cycles and based on the relative parasite burdens in individual horses. "Periodic, properly timed treatments can best benefit the health of the adult horse," Kaplan says.
Parasite control goals
The goal of parasite control is to limit parasite infections so animals remain healthy and avoid clinical illness. Treatments effective against adult parasite stages also help prevent further environmental contamination with infective stages. It's especially important to prevent egg shedding in individual horses with high egg-shedding capacity.
Simply stated, effective parasite control should minimize the risk of parasitic disease, control parasite egg shedding, maintain the efficacy of antiparasitic drugs and attempt to prevent further development of resistance. To achieve these goals, it's important to know the magnitude of an individual horse's egg shedding by performing periodic fecal egg counts.