Three worming strategies for horses in Canada

Last week I talked about the importance of fecal testing in your worming program. This week, I’m going to share some common deworming strategies for adult horses. I encourage you to work with your vet to create the best one for you and your farm. Well-meaning horse owners who bought paste wormer over the counter at their local tack store and wormed their herd without a well-formed strategy have created the resistance challenges we have today. Here’s an example:

According to Dr. Kirby Penttila of Burwash Equine Services, 10 or 20 years ago horse owners focused on deworming strategies to control large strongyles, AKA blood worms. They inadvertently created drug-resistant small strongyles. Today, this species is responsible for 99% of all eggs in managed horses (Source: Merck).

Active Ingredients in Wormers

Different actives control different worms. Make sure you’re administering the right active to kill the worms you need to kill. Don’t accelerate drug resistance by administering a product that will only wipe out weak worms and leave the strong worms to reproduce.


  • Brand names: Durvet Pyrantel, Strongid Paste, Exodus Paste
  • Worms controlled:

Fenbendazole / Oxibendazole

  • Brand names: Panacur, Safe-Guard Paste, Anthelcide EQ
  • Worms controlled:


  • Brand names: Equimax Paste (with praziquantal), Zimecterin Paste, Zimecterin Gold (with praziquantel), Quest Equine Gel (Moxidectin), Quest Plus Gel (Moxidectin with praziquantel), Agri-Mectin Paste, Bimectin Paste IverCare Paste
  • Worms controlled by Ivermectin:

Strategy 1: Worm three times a year

With the long cold winters on the Canadian Prairies, Alberta Vet Centre recommends this strategy for adult horses:

  • Spring (May/June): Worm with a moxidectin + prazquantel combo like Quest Plus
  • Summer (July/August): Worm with an oxibendazole like Anthelcide or a or fenbendazole like Panacur or Safe-Guard
  • Fall after the first hard frost (September/October): Worm with an ivermectin + prazquantel combo like Equimax

Strategy 2: Worm twice a year

Most vet clinic will tell you to deworm your horse twice a year at minimum – once in the spring and once in the fall after the first good frost. To make this strategy effective, establish a routine fecal count test on your farm. Send fecal samples to your vet before deworming and then again 10-14 days after deforming. That way, your vet can compare worm counts before and after the dewormer has had a chance to kill off the worm load in your horse. Then you can create a strategy for killing the types and populations of worms left.

Strategy 3: Only worm as needed

Author and lecturer Dr. David Ramey, DVM, reminds us that worms are parasites, and they have always lived in horses. When horses roamed freely, they would poop out the worms and carry on their way. It’s only with the advent of corrals, where horses and worms stay piled up together, that worms have become a problem and worm loads can reach a level that’s hazardous to the horse’s health.

Ramey says today’s parasite problems are a pasture management issue. If you don’t take steps to prevent environmental contamination following your deworming treatment, your horses will immediately become re-infected.

Getting your horse onto an “as needed” worming program works like this:

  • Time your worming application to ensure your horses are not shedding worm eggs during the first three months of grazing. This will reduce the build-up of infective larvae on the pasture later in the season. For Canadians, that means working with your vet to get your horse parasite-free over the winter. (Source: Equine Parasitology)
  • Get your horses used to electric fence so you can establish rotational grazing. Put small groups of horses in a small pen and move the pen frequently. The goal is to move the horses so frequently that they can only eat the top of the grass and don’t chew the pasture down to the dirt (where they can inject worms). (Source: The Horse)
  • Keep horses off that piece of land for three months or manually remove all manure with a fork before grazing horses there again.
  • Use fecal tests to assess worm load and create your “as needed” worming plan.
  • Only harrow paddocks during periods of high heat and little rain. (Source: The Horse)
  • Mow tall pastures at the end of the season so that the frost reaches the ground and kills the worms. Long grass and snow can insulate worms.

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