Q&A: Controlling Parasites in Horses

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Dr. Kenton Morgan, senior veterinarian, Equine Technical Services, Zoetis, shares his answers to some of the most common questions horse owners have about controlling parasites.

Q: When is the best time to deworm my horse?

A: Horse owners need to take advantage of the environment and deworm when parasite levels can be at their highest — during the spring and fall — per American Association of Equine Practitioners (AAEP) guidelines. Horses at greater risk may need more frequent anthelmintic, or deworming, treatments. Spring is the best time to treat for encysted small strongyles (strongyles in the larval stage). Quest Gel is a broad spectrum anthelmintic that with just a single dose, effectively treats and controls encysted small strongyles, bots and roundworms. A recent study shows Quest is nearly twice as effective in reducing egg counts as a double dose treatment of fenbendazole for five consecutive days.1

Q: How important is dosing to an accurate horse weight?

A: For your horse’s safety, and decreased risk for contributing to parasite resistance, it’s important to dose to your horse’s weight when deworming. Both under- and overdosing can contribute to safety and resistance issues. Download the Horse Weight Calculator mobile application from Zoetis to easily determine your horse’s weight.

Q: Should I consult with my veterinarian about my horse’s parasite control?

A: I encourage you to work with your veterinarian for advice on how to select the most appropriate dewormer for your horse. Your veterinarian can perform a fecal egg count (FEC) test to determine the necessary frequency of deworming treatments. One FEC per year is recommended for adult horses to help determine parasite levels and efficacy of the treatment. Once you have established a baseline, work together to develop an Individualized Deworming™ program.

Q: Why is an FEC recommended?

A: An FEC gives a quantitative assessment of your horse’s worm burden. The AAEP considers an FEC to be the best assessment of parasite burden to identify the frequency of treatment needed. By employing a fecal egg count reduction test (FECRT) with your veterinarian, you can determine whether your horse has a parasite resistance issue. To perform an FECRT, your horse’s fecal sample is collected and tested before deworming and again 14 days after deworming. This practice can help you determine when and with which product to treat for parasites.

Q: Is rotational deworming still a viable equine parasite control method?

A: This concept goes back decades and, overall, is highly discouraged. By deworming every horse every few months, horse owners can do more harm than good — increasing the horse’s risk for parasite resistance. When parasites are overexposed to certain treatments, they can become resistant, leaving fewer effective treatment options. Encysted small strongyles, the most common parasite of concern in adult horses,2 have been shown to have widespread resistance to fenbendazole.3 Moxidectin, the active ingredient in Quest and Quest PLUS, continues to be effective.1 Quest and Quest PLUS are safe for use in a variety of horses and are the only products approved to treat encysted small strongyles in breeding mares and stallions.

Q: What additional practices do you recommend to control equine parasites?

A: Make sure your horse consumes his grain and hay in a container or hay rack, not on the ground. Composting manure and clipping pastures also can help control parasite populations. To help eliminate larvae, pasture rotation also is good practice, either by taking horses off the pasture or rotating in another species, such as cattle.

Take a proactive approach to controlling parasites. Visit IDMyHorse.com for additional information and resources.

Do not use Quest Gel or Quest PLUS Gel in foals less than 6 months of age or in sick, debilitated and underweight horses. Do not use in other animal species, as severe adverse reactions, including fatalities in dogs, may result.

About Zoetis

Zoetis is the leading animal health company, dedicated to supporting its customers and their businesses. Building on more than 60 years of experience in animal health, Zoetis discovers, develops, manufactures and markets veterinary vaccines and medicines, complemented by diagnostic products, genetic tests, biodevices and a range of services. Zoetis serves veterinarians, livestock producers and people who raise and care for farm and companion animals with sales of its products in more than 100 countries. In 2016, the company generated annual revenue of $4.9 billion with approximately 9,000 employees. For more information, visit www.zoetisUS.com.

1. Mason ME, Voris ND, Ortis HA, et al. Comparison of a single dose of moxidectin and a five-day course of fenbendazole to reduce and suppress cyathostomin fecal egg counts in a herd of embryo transfer-recipient mares. J Am Vet Med Assoc. 2014;245(8):944-951.

2. American Association of Equine Practitioners. AAEP Parasite Control Guidelineshttps://aaep.org/guidelines/parasite-control-guidelines. Accessed July 14, 2017.

3. Kaplan RM. Anthelmintic resistance in nematodes of horses. Vet Res. 2002;33(5):491-507.