Deworming 101: What Updated AEEP Guidance Means for Horse Owners
Deworming is an important part of any routine health care for all horses, no matter where you live. The autumn months, as the weather and pasture changes from lush and warm to cool and dry, are a great time of year for horse owners to deworm.
Last year, the Association of American Equine Practitioners updated deworming guidance, which affects how horse owners should consider their deworming routine. It states that most adult horses should be dewormed twice a year at most, unless the results of a fecal egg count (FEC) test suggest otherwise.1 To help further delay development of anthelmintic resistance and maintain long-term effectiveness of current deworming products, practitioners discourage fixed-interval, year-round deworming and rotating dewormers.1
“There aren’t new drugs in the pipeline for deworming, so it’s important we maintain the effectiveness of the tools we currently have,” said Abby Sage, an Equine Technical Services Veterinarian with Zoetis, the maker of Quest® Gel (moxidectin) and Quest® Plus Gel (moxidectin/praziquantel). Dr. Sage joined the hosts of the Heels Down Happy Hour Podcast to discuss deworming protocols and seasonal horse health topics. “Over time, parasites can adapt to the active ingredients used in the drugs and survive treatment.”
Dr. Sage generally recommends Quest Gel with moxidectin in the spring grazing season and Quest Plus Gel with moxidectin and praziquantel active ingredients in the fall grazing season.
“The updated AAEP guidelines, asks horse owners to work with their veterinarians to conduct FEC tests to identify high-shedding horses, which would require additional targeted deworming treatments,” Dr. Sage said.
In general, the updated guidance calls for deworming healthy, adult horses twice a year—reserving additional treatments for those high shedders.1
Dr. Sage breaks down the topic of dewormers for us below.
How Do Fecal Egg Counts Work?
Fecal egg counts are a way for veterinarians to measure how many parasite eggs are being shed in a horse’s manure. A vet will take a small manure sample and examine it under a microscope to determine the egg count. This test helps determine which horses are carrying the heaviest parasite burdens and can inform if they need additional treatment.
It’s widely shared in the veterinary community that up to 30% of the horse population is considered “high shedders,” said Dr. Sage, which means they carry a higher load of parasites that contribute to more reinfesting of all horses on a property.2
An FEC test is important because it helps horse owners determine an individual treatment plan for each horse, and it can be useful to track the effectiveness of deworming treatments, which means it also has potential to help combat resistance and over-treating when it’s not necessary.
One misconception Dr. Sage said she hears all the time is that horses should have zero parasites.
“This isn’t the case at all,” she said. “All horses will carry parasites and that’s totally OK. Deworming is about reducing the overall count and protecting against harmful parasites, not ridding your horse of every single one.”
Which Dewormer Product Is the Right One for My Horse?
There are several deworming products, many with different active ingredients, available at the local feed store. But which one is the right choice? And for what time of year?
Active ingredients are important, Dr. Sage said. Not all use the same, and each ingredient is meant to combat a different type of parasite. Your geographic location and time of year can make a difference too. It’s incredibly important to make this decision with guidance from your veterinarian.
“I typically recommend the primary ingredient in the Quest line, Moxidectin, which works against small strongyles, large strongyles (bloodworms), bots, pinworms, hairworms and stomach worms,” she said. “Tapeworms and small strongyles as the two parasites of great concern in adult horses.3,4 Roundworms are considered a greater risk to foals during the first 6 to 8 months of age.1 “
Dr. Sage recommends using Quest Gel in the spring grazing season, around April or May, and Quest Plus Gel at the end of grazing season, in October or November. Here is a yearly dewormer guide and quiz to help you and your veterinarian determine the best deworming protocol for your horse.
Quest Plus Gel is the dewormer recommended for fall use since it is the only dewormer that has active ingredients to help treat encysted small strongyles and tapeworms in a single dose, in addition to its broad-spectrum support that also treats large strongyles, bots, pinworms hairworms and stomach worms.5†
Deworming Best Practices
Dr. Sage said that the most important parts of managing parasites in horses is in staying on top of seasonal deworming and working with a vet on those fecal egg counts. “Our goal is always for horse owners to take stock of their current practices to ensure they are deworming so that treatment can remain effective,” said Dr. Sage.
That’s also the inspiration behind the Zoetis “Buy Less Dewormer” campaign.
“It’s important to note that no parasiticide can eliminate all parasites, but a single dose can treat many types,” Dr. Sage concludes.
IMPORTANT SAFETY INFORMATION: 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. Consult your veterinarian for assistance in the diagnosis, treatment, and control of parasitism.
†Compared to the labels of Panacur® POWERPAC, Zimecterin® and Zimecterin® Gold.
- American Association of Equine Practitioners. AAEP Internal Parasite Control Guidelines. https://aaep.org/resource/internal-parasite-control-guidelines/. Accessed October 11, 2025.
- Young A, Finno C. Intestinal Parasites in Horses. School of Veterinary Medicine, University of California, Davis. August 12, 2022. https://ceh.vetmed.ucdavis.edu/health-topics/intestinal-parasites-horses. Accessed October 11, 2025.
- Proudman CJ, FrenchNP, Trees AJ. Tapeworm infection is a significant risk factor for spasmodic colic and ileal impaction colic in the horse. Equine Veterinary Journal. 1998;30(3):194.
- Lawson, A., Malalana, F., Mair, T. Larval cyathostominosis: Clinicopathological data and treatment outcomes of 38 hospitalised horses (2009–2020). Equine Veterinary Education Vol 35, Issue 8.
- Corning, S. Equine cyathostomins: a review of biology, clinical significance and therapy. Parasites Vectors 2 (Suppl 2), S1 (2009).
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