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DEWORMING RECOMMENDATIONS – Why change our deworming strategy?

Resistance is real
Equine parasite resistance is on the rise. Small strongyle resistance to the benzimidazole (Panacur, Anthelcide) and pyrantel pamoate (Strongid) dewormer classes and ascarid resistance to macrocyclic lactone (Ivermectin, Quest) dewormer class have been reported in the United States. Additionally, there are no new deworming drugs currently in development. Keeping the effectiveness of the drugs we have for as long as possible is therefore very important. So we want to make sure we use the right deworming drug at the right time.

Horses tend to fall into 1 of 2 categories regarding their natural immune resistance to intestinal parasites.

– Low-Shedders: Approximately 70% of our horse population in the United States has a good natural immune response to intestinal parasites. Meaning, their own body keeps the parasites in check and at very low numbers within their body.

– High-Shedders: Approximately 20-30% of our horse population cannot naturally keep their intestinal parasites in check. The parasites may not always cause clinical disease in these horses but the parasites are able to reproduce at high rates and contaminate the environment. While high shedders only account for a small part of the horse population, they produce 80% of the parasite eggs on the pasture.

** Conventional deworming strategies over-treat many horses, but under-treat high shedders. High shedders need to be dewormed more often than their low shedding herd mates to prevent contamination of the pasture with large numbers of parasite eggs. Low shedding horses may only require deworming twice a year, depending on their management situation. A simple test called a Fecal Egg Count will identify high shedding vs. low shedding horses. This test is best performed at least 3 months after the last deworming treatment.

A few worms are OK
The goal of previous deworming strategies was to eliminate all parasites from the horse. This was not a realistic endeavor and has in part led to overuse of deworming products. Our new deworming strategies should be focused on reducing transmission of parasites, keeping parasite burdens below harmful levels, and treating clinically affected horses. In this manner, a population of susceptible parasites is maintained to dilute the resistant genes in the population and thereby keeping our deworming medications effective as long as possible.

Environment matters
Horses in low density vs. high-density populations have different exposure levels to parasites. Additionally, horses living in Minnesota have very little transmission of parasites during winter months because the eggs freeze and die when the manure hits the ground. These things matter and need to be accounted for when we set up a deworming program for your horse.

**Check for resistance
A Fecal Egg Count Reduction Test (FECRT) is the preferred method for testing for resistance. This test is basically two Fecal Egg Counts; one done before deworming and another two weeks after deworming. If your horse has a HIGH fecal egg count, we may recommend doing a FECRT.

In summary: We want to be more involved in your horse’s deworming schedule. We can help you determine if your horse is a high-shedder or low-shedder (by performing a Fecal Egg Count) and tailor a deworming program to best fit their needs.

Example Deworming Program

(these are only examples and not meant as specific guidelines especially if you have not had a fecal egg count)

Low Shedder:
March/April: Fecal Egg Count &/or deworm w/ Ivermectin, Panacur, or Safeguard
July: Deworm with Quest or Quest Plus
Oct/Nov (after a hard frost): Fecal Egg Count (if not done in the spring) & deworm with Equimax or Zimectrin Gold (products containing praziquantel)

High Shedder:
March/April: Fecal Egg Count & deworm w/ Ivermectin or Panacur or Safeguard
June: Deworm with Quest or Quest Plus
September: Fecal Egg Count & deworm with Ivermectin or Oxibendazole (FECRT may be recommended)
Oct/Nov (after a hard frost): Deworm with Equimax or Zimectrin Gold

Deworming Foals: Foals can build up a parasite burden much faster than a mature horse. For this reason, we recommend deworming foals MONTHLY from 1-2 months of age until 12 months of age.

Month 1: Panacur or Safeguard
Month 2: Ivermectin
Month 3: Panacur or Safeguard
Month 4: Strongid
Month 5: Panacur or Safeguard
Month 6: Ivermectin
….and so and so forth….

Tips for deworming:

– Give the dewormer before feeding your horse their grain. Or, if the horse has a mouthful of hay or grain, remove them from food sources for a few minutes. If their mouth is full of food they will spit out the dewormer with the half-chewed food.
– After giving the dewormer, hold the horses head up the air for a moment or two. Hold the deworming syringe sideways in their mouth, like a bit, to encourage them to move the dewormer around their mouth and swallow. This way they won’t be as likely to spit out the dewormer.
– For young and elderly horses, as well as ponies and minis, be sure to dose the product appropriately according to estimated weight.