Equine intestinal worms have evolved considerably over the last 20 years, and so has our understanding of their life cycles. We now know that in any given herd, 20% of the individual horses carry 80% of the intestinal worms. These few animals are responsible for shedding most of the eggs that contaminate the environment and infect everybody with the next generation of parasites. Generally, this characteristic is a constant through the horse’s life, meaning that those with heavy burdens will always be more susceptible to reinfection despite regular deworming, while others are very resistant and have few intestinal worms at any given time.

So, if each horse has a consistently different level of intestinal parasitism, then treating everybody with the same deworming product rotation at the same two-month interval doesn’t make much sense. This approach results in most horses being exposed to unnecessarily frequent medical treatments, encourages the growth of drug resistant parasites, and is expensive. If we continue to use dewormers in this manner, soon none of them will be very effective and we will be unable to control intestinal parasites.

McKee-Pownall Equine Services has worked with a board-certified parasitologist to create an approach to deworming based on the latest research, in order to ensure that your horse receives exactly the right medication at exactly the right times, based on the identification of their carrier status. Fortunately, we can detect and classify these high, medium, and low burden horses through fecal examinations at appropriate times of the year. Further fecal examinations will determine if the particular medication used is still effective for reducing the intestinal worm population in that horse. The November treatment will also control tapeworms. Please review the chart below, which outlines the individual treatment strategy for each category:

Most horses are considered to be “low shedders” which means they have developed some natural resistance to intestinal parasites and only need targeted deworming twice yearly.

A small number of horses are “high shedders”. These horses have poorer natural immunity and carry a larger number of worms. These horses will re-infect the rest of the herd through their manure. These horses often need to be dewormed 3-4 times per year based on fecal results.

The main parasite of adult horses are small strongyles, ivermectin and moxidectin are the best dewormers for this class of parasite.

Paraziquantel targets tape worms and should be used once per year.

Reducing exposure of your horse to parasites is as important as treating with a deworming product. This can easily be done by removing manure from pastures & paddocks at least two times per week. If you prefer to spread manure on your pastures, be sure to compost it first. Properly composted manure can be safely spread in the fall will little risk to horses on the pasture. Here is a link to a helpful website to get you started on composting your manure pile:

http://whatcom.wsu.edu/ag/compost/horsecompost.htm

When new horses arrive on your farm, a fecal exam should be run, treated appropriately and keep it separated for at least 3 days before interacting with your horses.

Broodmares, foals and horses travelling to warmer climates in the wintertime require different treatments based on their individual circumstances.

• Broodmares should be dewormed the day after foaling to prevent transmission of milk worms to the foal

• Foals should be dewormed at 2mos and 5mos with double dose fenbendazole(Panacur or Safegard) to target ascarids, 7-9mos with ivermectin and praziquantel to target small strongyles and tapeworms, FEC test at 10-12mos(depending on last deworming date)

Follow AAEP guidelines for horses 1 to 3 years of age and base deworming on FEC results
Most horses under 3 years of age will need to be treated as high shedders while they develop immunity
Horses under 1 year of age should never receive moxidectin(quest or quest plus)

• Horses travelling to warmer climates in the wintertime will require an additional February treatment

Miniature horses require a slightly different deworming approach, as they should never receive moxidectin products(quest or quest plus). Miniature horses should be treated according to the following schedule.

2024 AAEP Internal Parasite Guidelines https://aaep.org/resource/internal-parasite-control-guidelines/

If your miniature horse shares a pasture with a donkey, or if habronema is a risk in your area, a slightly modified schedule will be required. Please speak to your veterinarian regarding the specific treatments needed to address these issues.

What guidelines do you have for deworming my horse?

As an individual horse owner, what biosecurity measures can I use to protect my horse on a day to day basis?