Horse Dewormer FAQ with an Equine Veterinarian

Key Takeaways

• Internal parasites are a major concern for horses, with small strongyles now posing the greatest risk to adult horse health due to their ability to encyst in the intestinal lining and trigger inflammation, colic, and weight loss.
• Modern deworming has reduced the threat of large strongyles, but veterinarians now emphasize targeted control of small strongyles as the cornerstone of equine parasite management.
• AAEP guidelines recommend treating encysted small strongyles at least once per year, with moxidectin identified as the most effective active ingredient for this stage.
• A minimum twice-yearly deworming schedule (spring and late fall/early winter) is recommended for adult horses, with fecal egg count testing used to identify high shedders that may need additional treatments.
• Deworming works best when paired with good management practices, including manure removal, pasture rotation, and feeding hay and grain off the ground to reduce parasite exposure.

There are more than 150 species of internal parasites that can infect horses, making equine deworming a critical part of your horse’s overall equine wellness program (in addition to vaccinations against common diseases in horses).

Learn the ins and outs of deworming horses from Kenton Morgan, Senior Veterinarian, Equine Technical Services with Zoetis. Below, he answers frequently asked questions about worming horses, common worms in horses and how veterinarians today are recommending horse owners implement a horse worming schedule.

Do large stronglyes still present the highest threat to horses?

Decades ago, large strongyles (bloodworms) posed the greatest threat to horse health. But thanks to modern dewormers, this parasite can be more easily controlled and should no longer keep you up at night. The greatest parasite concern for adult horses today is the small strongyle, making it imperative that your horse receives timely treatments each year.

Why are small strongyles harmful to a horse's health?

Small strongyles pose significant risks for adult horses because their larvae (immature parasites) can burrow into your horse’s intestinal lining. This part of their lifecycle is called “encysting.” The emergence of these encysted larvae from the gut wall can be extremely concerning. Experts believe this process can cause harmful inflammation of the gut, which could be associated with a host of serious health problems such as increased risk for colic and weight loss over the course of your horse’s adult life.

How often do you worm a horse against small strongyles?

The American Association of Equine Practitioners (AAEP) Parasite Control Guidelines specifically recommend treating the encysted stage of small strongyles at least once per year to protect your horse’s health.

How do you protect against small strongyles?

Based on AAEP guidelines, [the active ingredient] moxidectin remains effective against small strongyles and is the deworming option experts recommend.

How do you control worms in horses?

Moxidectin, the active ingredient exclusive to Quest Gel and Quest Plus Gel in the United States, is the treatment of choice for treating small strongyles. Quest Gel is the only dewormer approved by the U.S. Food and Drug Administration to control encysted stages of small strongyles, large strongyles, pinworms in horses, horse bots (and other labeled parasites) in a single dose, making it the optimal treatment option for deworming. It also can suppress small strongyle eggs for 90 days, making it a powerful choice for parasite control.

A deworming schedule for horses can look very different from horse-to-horse, based on how horses are housed in their stable or pasture environments. Considering common worms in horses, what is recommended by veterinarians today for a horse worming schedule?

To maximize results against small strongyles, tapeworms in horses and other horse parasites, every adult horse should be dewormed in the spring, at the beginning of grazing season in your region, and in late fall/early winter, toward the end of grazing season in your region. One or both of these treatments should target the encysted form of small strongyles, and the fall treatment should also target tapeworms. While this twice-annual deworming is the minimum that parasite experts recommend for all adult horses, it’s important to also have your veterinarian conduct a fecal egg count (FEC) test on each horse in your care at least once per year. This FEC will identify horses in your herd that are “high parasite egg shedders” and may need a third, and possibly fourth, deworming treatment for small strongyles over the course of the year.

In addition to worming horses, help control parasites on your property by ensuring horses consume their grain and hay off the ground in a feeder or hay rack. Also, remove manure daily, clip pastures and consider pasture rotations. By removing horses from the pasture and rotating in another species, such as cattle, you can help eliminate parasite burden from the field. An effective horse wormer, along with these deworming protocols, will help provide your horses the protection they need from the most concerning worms in horses.

Give your equine best friend the parasite protection he deserves.

About the author: This content was originally provided by Zoetis, with minor additions included from Valley Vet Supply.

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