Deworming treatments are often a regular component of horse health maintenance, but many owners may not understand the best schedule for their horse. While deworming regimens vary by region, there are some ground rules for owners to follow as they work with their veterinarians on a proper deworming schedule.
Dr. Thomas Craig, professor at Texas A&M University College of Veterinary Medicine & Biomedical Sciences (CVM), who specializes in epidemiology and the control of internal parasites in equines and grazing animals, offered some insight into deworming. Craig explained that in a given population of horses, about 20 percent will have 80 percent of the total internal parasites of the herd.
Another basic guideline is that deworming should be based on the age of the horse. There is a drastic difference in the deworming needs of a foal (less than a year) and an adult horse.
“What’s effective in adults may not be effective in foals,” Craig said.
Craig suggested deworming foals for the first time at two months of age. Parascaris equorum are of particular concern at this age.
“I recommend using fenbendazole, a broad spectrumbenzimidazole anthelmintic, such as Safe-Guard, or a pyrantel dewormer such as Strongid for foals two months old,” Craig said.
As the foal matures, it is recommended that the same treatment be used at four and six months of age. When the foal reaches a year old, Craig suggested using an ivermectin or moxidectin treatment for deworming.
When worming adult horses (older than one year), the approach changes considerably. The most dangerous parasitic threat to horses are small strongyles, which are present in most horses. Craig recommended testing mature horses through fecal samples to determine the number and types of parasitic eggs in the horse’s digestive system.
“After strongyles, the rest of parasitic control is really just a numbers game,” Craig said. “In older horses, you really only need to deworm horses with high numbers of parasites. Adult horses with less than a few hundred eggs per gram can be relatively left alone.”