Horse Illustrated Magazine

You’ve learned to use fecal testing and you know horses should be dewormed according to their individual needs, and not all be on the same program. But if you haven’t added a daily horse dewormer to your program, you could be overlooking a way to provide continuous protection against many equine parasites.

The paste dewormer you administer occasionally is considered a “purge” dewormer. These products are designed to interrupt the infestation cycle of parasites and kill them.

A daily horse dewormer is different in that it’s designed to create a barrier to parasites before they cause infestation.

“A barrier dewormer is probably the best way to protect an individual horse against parasites,” says Tom Kennedy, Ph.D., a veterinary parasitologist based in Westport, Wisc.

Daily dewormer products protect against as many as 18 species and stages of equine parasites, including pinworms, adult large strongyles, adult small strongyles and their fourth-stage larvae, and adult ascarids and their fourth-stage larvae.

“Daily dewormers work against the bulk of parasites we’re concerned with in horses, especially strongyles, which are the parasites of greatest concern with adult horses, and ascarids, the biggest issue with foals and young horses,” says Kennedy.

How it Works

Pyrantel tartrate, the standard anthelmintic (deworming) drug used in daily deworming products, has a wide margin of safety and can be used on horses of all ages, from foals to seniors, including pregnant and nursing mares.

“Pyrantel tartrate is not well absorbed by any mammal; it passes through the horse,” says Kennedy.

Whether a grazing horse picks up parasite eggs or larvae, a daily horse dewormer product begins working on the parasites in larval form once they’re in the horse’s digestive tract.

“We’re basically using the horse as a ‘mixing vat’ to expose the larvae to the drug, mixing the dewormer into the gut contents of the horse,” explains Kennedy. “When the larvae are picked up by the horse or the larvae come out of the eggs the horse has picked up, they start to metabolize, picking up nutrients in the horse’s gut. The dewormer is present and starts working on the parasites wherever they’re having their normal growth process. With strongyles, much of this happens in the large intestine. With ascarids, it happens in the small intestine.”

The drug works directly on the neuromuscular system of parasite larvae to paralyze them, then they pass out of the horse’s body in the manure.

Getting Started

Talk to your veterinarian before starting a daily horse dewormer. Your vet may recommend first administering a broad-spectrum dewormer, such as ivermectin, to get rid of any worms that may already be in the migration cycle.

“Over the years, I’ve recommended daily dewormer for many of my clients,” says Sam Crosby, DVM, who has worked as sales veterinarian at Heritage Place sales facility in Oklahoma City since 1995 and maintains his own equine practice in Arcadia, Okla.

Crosby says daily dewormers have been an effective tool for clients with horses that still seem to have parasite problems despite being on a traditional deworming program. He advises using an ivermectin paste dewormer before starting on daily dewormer.

Read the directions on a daily horse dewormer and you’ll see it’s fed according to weight. Use a weight tape to get a good approximation of how much your horse weighs.

Because a daily dewormer is mixed with the horse’s grain ration, if you want to use it on foals, they need to be consistently eating their own feed.

Take the “daily” part of the name seriously, advises Kennedy. “You have to use it every day. It’s a barrier dewormer, and a break in the barrier [by skipping a day or more] can allow worms to develop.”

Even when you faithfully use a daily dewormer, that doesn’t mean you’ll never have to use a paste dewormer again, since daily dewormers aren’t effective against all species of equine parasites. For example, if your horse is exposed to bot flies or tapeworms, you should treat him with a purge dewormer labeled effective against these parasites at least once a year.

More Than One Tool

“Controlling parasites in horses is about management; it’s not just about one tool. You need to use them all,” says Kennedy.

An effective parasite control plan includes:

◆ Manure and pasture management

◆ Fecal testing

◆ Purge dewormers (as indicated by fecal testing and veterinarian recommendation)

◆ Daily horse dewormer
You may be inadvertently contributing to horses getting reinfected by parasites if you don’t properly manage turnout areas and pastures. Strongyle eggs pass in the horse’s manure, and once those larvae hatch, they can be picked up by grazing horses, continuing the cycle.

Keep your horse’s environment as manure free as possible to help limit parasite infection.

◆ Don’t feed hay on the ground.

◆ Don’t spread stall waste on pastures currently used for grazing.

◆ Don’t drag fields to spread manure if you currently use them for turnout or grazing.

If you must drag, only do so during hot, dry weather (not cool, wet weather), then keep horses off the field for at least two weeks, preferably four.

This article about daily horse dewormer appeared in the March 2021 issue of Horse Illustrated magazine. Click here to subscribe!