Should You Deworm Horses After the First Frost?

By now, many horse owners have likely heard that rotational deworming is outdated. More than half of horse owners are working with veterinarians to use fecal egg counts (FEC)1 to determine customized deworming schedules. As more horse owners turn away from rotational deworming, different questions arise around timing.

There are two main parasites–bots and tapeworms–that are targets for fall or winter timing.2


Bots are the larvae of the botfly. Since these flies are common in barns and pastures where horses live, horses could become infested with bots, and often horse owners will recognize the botfly eggs on their horse’s hair.3 Deworming with ivermectin yearly, during late fall or early winter, is recommended as a cleanout treatment for bots, which will help decrease transmission in the next season.2


Adult tapeworms are fairly common and live in the intestine of the horse;3 however, they are difficult to diagnose. Horse owners will rarely see tapeworm segments in manure, unlike some other parasites, and there is no reliable diagnostic test for active tapeworm infection.4

But because tapeworms have potential to cause disease like colic, a properly timed tapeworm treatment is beneficial.2 In most U.S. areas, deworming with praziquantel in combination with ivermectin should be given in late fall or winter.2 Cold weather means the end of tapeworm transmission, and that timing for treatment helps diminish additional transmission the following grazing season.2 No generic ivermectins offer tapeworm control.

“Parasite control is an important part of any horse health program,” said Hoyt Cheramie, DVM, MS, DACVS, manager, Merial Large Animal Veterinary Services. “Choosing the right deworming product and the right timing for it is key.”

ZIMECTERIN® Gold (ivermectin/praziquantel) is a broad-spectrum dewormer that controls more species and stages of equine parasites–including the tapeworm Anoplocephala perfoliata–than any other brand.5,6 Ultimately, each farm should develop its own program tailored to the specific needs of the farm and each animal, with veterinary guidance. There is no such thing as a “one size fits all program.”2

More information about effective deworming strategies and ZIMECTERIN® Gold (ivermectin/praziquantel) can be found at

Merial is a world‐leading, innovation-driven animal health company, providing a comprehensive range of products to enhance the health and well-being of a wide range of animals. Merial employs 6,100 people and operates in more than 150 countries worldwide with over €2 billion of sales in 2014. Merial is a Sanofi company.

Important Safety Information: Not for use in humans. Keep this and all drugs out of reach of children. In horses, there have been rare reports of swelling and irritation of the mouth, lips and tongue following administration of ZIMECTERIN Gold. These reactions have been transitory in nature. Do not use in other animal species as severe adverse reactions, including fatalities in dogs, may result.

®ZIMECTERIN is a registered trademark of Merial. ©2015 Merial, Inc., Duluth, GA. All rights reserved. EQUIZIM1507 (10/15)

1. American Horse Publications. 2015 AHP Equine Industry Survey. July 2015.

2. AAEP Parasite Control Guidelines 2013, Accessed June 1, 2015.

3. Internal Parasites in Horses. American Veterinary Medical Association. September 2010.

4. Reinemeyer C, Nielsen M, McArthur M. Parasite control as a profit center. EquiManagement. 2010;26.

5. Based on data provided on the ZIMECTERIN Gold label.

6. Based on data provided in FDA Freedom of Information summaries






"*" indicates required fields

The latest from Stable Management, the #1 resource for horse farm and stable owners, managers and riding instructors, delivered straight to your inbox.

Additional Offers

Additional Offers
This field is for validation purposes and should be left unchanged.