The Stable Secretary Blog

Deworming Horses

If you were to ask 100 people- from veterinarians to trainers- about the best treatment for deworming horses, you will most likely receive a plethora of differing responses.

How to deworm horses is a topic that has had many opposing recommendations over the years. Before we get into deworming horses, let’s first discuss the issue of worms. Horses are grazing animals; parasites- such as tapeworm, roundworm and strongyles- are part of a normal population of organisms that live in the intestines of all grazing animals.

Many years ago, before horses became domesticated, horses and parasites got along just fine. Horses developed an immune response in their intestinal lining to help keep the parasites under control, and there were hardly any parasite issues. However, when people came along and began to put horses in fenced-in pastures or small areas, there was nowhere for the horses or worms to go and so the worms all piled up in the small areas and became a much bigger problem to horses.

When these problems started to occur, deworming medications became more and more popular and many vets recommended that horses be given medications every two months, with different dewormer medications offered to make sure the horse was protected against all types of potentially damaging internal parasites.

The four most common types of internal parasites that they were protecting against are:

• Strongyles (blood or red worms)
• Ascarids (roundworms)
• Tapeworms, and
• Bots (flies)

We now know that each species of parasite affects a horse in its own way. The “traditional” approach to deworming, whereby all horses are treated every 2 months or so, was designed in the 1960’s. This program was designed to specifically target a parasite called Strongylus vulgaris, a type of parasite called a large strongyle, which at the time caused horses significant problems. Thankfully, the program pretty much worked; Strongylus vulgaris is now a rare parasite and is practically irrelevant in managed horses.

However, as a result of horses getting so many medications to deworm and protect them, there is now a worm population that is becoming increasingly resistant to all of the useful deworming agents. Therefore, the old rules about deworming have changed due to this drug resistance, and the every two month treatment is outdated. The goal previously was to rid your horse of all parasites- but we now know that that is impossible, and so the current thinking is to simply limit parasite infections, rather than rid of them completely, so that horses remain healthy.

It is now common knowledge that horses under the age of 3 are more susceptible to parasite infections than older horses, and should therefore be treated more often than older horses. Older horses, on the other hand, should be treated as individuals and not all on the same routine. The current recommendation is that they receive only one or two treatments per year, depending on the climate where the horse lives and whether the horse lives with other horses. If a horse lives alone or in a stable, the frequency of treatments would be less than for a horse who lives with other horses.

A quick internet search will show many cost effective dewormer pastes, gels and pellets. Depending on your horse’s age and living conditions, you can work with your vet on the best dewormer program to keep your horse safe. Along with the medical treatment, it is also essential to conduct fecal exams to test your deworming program’s effectiveness, and to consistently clean up manure to control the horse’s environment.

You can track deworming, fecal counts, and other health events and procedures, in Stable Secretary.