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DEWORMING YOUR HORSE

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Daily Dewormers: A Different Approach to Parasite Control

By Cynthia McFarland

If you’re like most horse owners, you’re under the impression that deworming is something that takes place a few times a year. But did you know there’s a different way to protect your horse from certain parasites?

Daily dewormers are intended as a barrier against parasites and therefore used every day as compared to “purge dewormers,” which are administered weeks or months apart.

horses in snowy pasture

Tom Kennedy, Ph.D., a veterinary parasitologist based in Westport, Wisconsin, explains the difference between these two approaches to deworming.

“Purge deworming with one of the several products approved for such use is based on the premise that the only way to treat parasites is to allow the horse to accumulate the worms from the environment so that we can treat them,” Kennedy notes. “The worms go through their normal life cycle in the horse and when they reach the life stage where the purge is effective, we can kill the worms.”

Purge dewormers interrupt the infestation cycle of the parasites but don’t prevent their larvae from migrating through the horse, which is the cycle when most internal damage takes place.

On the other hand, a daily dewormer prevents parasite infestations from occurring in the first place. These products protect against an extensive array of species and stages of equine parasites, including adult large strongyles, adult small strongyles, fourth-stage larvae, pinworms and adult ascarids.

“Daily dewormers for horses are designed to be a ‘barrier’ to worms,” says Kennedy. “With the only approved anthelmintic used in a daily dewormer–pyrantel tartrate–we feed the daily dewormer which is conveniently mixed into the gut contents of the horse. When worm larvae enter the horse via the mouth and travel down the digestive tract, they encounter the drug through the entire journey and are killed before they can complete the life cycle.”

A DAILY DEWORMER PREVENTS PARASITE INFESTATIONS FROM OCCURRING IN THE FIRST PLACE.

Pyrantel tartrate works by attacking the neuromuscular system of parasite larvae. In essence, it paralyzes them and they are passed out of the horse’s body with the manure. Because the parasites are killed before they can migrate through the horse’s digestive system, they aren’t able to inflict serious damage. An added benefit is that pyrantel tartrate breaks down in sunlight after passing through the horse’s system, so you don’t have to worry about harmful effects on the environment.

Even if your horse is on a daily dewormer, you may find it necessary, on occasion, to use an additional purge deworming product to cover “exposure gaps.” For example, pyrantel tartrate is not effective against botfly larvae or tapeworms (cestodes). If your horse is exposed to these parasites, you’ll need to treat him with an effective botfly and cestocidal product as described in labeling for those products.


Could Your Horse Benefit?

Kennedy explains that daily deworming makes sense for a variety of horses in a number of different situations. These include mares before and after foaling, horses stabled with other equines when you don’t know if/when they have been dewormed, and performance horses traveling to venues where the parasite contamination level may be of concern. Young foals and elderly and debilitated horses also stand to benefit from a daily deworming routine.

Always read the label and follow usage directions carefully. There is a wide safety margin, typically making daily dewormers safe to use on horses of all ages, including breeding stallions and mares at any stage of pregnancy or lactation. Foals need to be consistently eating a grain mix in order for you to give a daily dewormer, which commonly begins between the ages of two and three months.


Getting Started

Before you embark on a daily deworming program, your veterinarian will likely recommend administering a broad spectrum-dewormer, such as ivermectin. This is to rid the horse of blood worms that may be in the migration cycle.

A daily dewormer product is fed according to weight, so you’ll need to use a weight tape to get a close estimation of how much your horse weighs.

If you’re using a daily dewormer, remember that it must be given every day. Skipping a day allows lowered levels of drug in the gut contents, and a loss of continuous efficacy.

You’re already ahead of the game if you’re using fecal egg count testing, which many veterinarians recommend. This testing is still helpful if you’re using a daily dewormer. Fecal egg counts are an effective tool to monitor the effectiveness of any deworming program. Your veterinarian can explain how and when these simple tests should be done.

“Fecal egg count is also helpful to use in a rotational deworming program to determine which products in the rotation are effective,” adds Kennedy. “Rotation of the chemical class of dewormer is one way to manage the useful life of the product on the market.”

Unlike some other classes of deworming drugs, resistance to pyrantel-based dewormers has not become a problem, which is good news for horse owners using daily dewormers.

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