Equine dewormer is a treatment that is familiar to almost every horse owner. That’s because every horse is at risk of getting infected with worms. However, there are also risks associated with not treating worms in horses, such as damage to the intestinal wall or respiratory problems. There are also risks with over-treatment, such as causing dewormer resistance. While equine experts have different approaches on how and when to deworm, horse owners should use a combination of preventative and treatment measures.

Most Common Intestinal Parasites Found in Horses

When choosing a dewormer, it’s important to use a product designed for the type of parasite your horse has. This is why most experts recommend testing your horse at a vet before treating them. They also recommend testing after the treatment to ensure it has worked.

There are many species of worms in horses, but the most common include:

Small Strongyles – Small strongyles, or small redworms, are the most common worm found in horses. They live in the horse’s large intestine without resulting in the degree of damage caused by large strongyles. Therefore, horses might have significant numbers of these worms without exhibiting any signs. However, heavier infections might cause a horse to show signs of poor condition, inflammation of the large intestine, and diarrhea.

Large Strongyles – Large strongyles are also called roundworms, blood worms, or red worms. Horses become infected by ingesting larvae in the pasture. After ingestion, the larvae become active in the intestine and migrate throughout the circulatory system before maturing in the large intestine. An infection can lead to anemia, weight loss, weakness, and occasionally diarrhea.

Infections from small and large strongyles typically occur together. There are many small and large strongyles species, some of which cause more serious infections in horses than others. This is one reason that having your horse tested is important. The vet can identify the exact type of infection and the best route for eliminating the specific type of parasite. In most cases, the vet will recommend treatment using an effective strongid dewormer.

Tapeworms – Tapeworms belong to a class of parasites called cestodes. Adult tapeworms are flat and about three inches in length. Infections with these worms aren’t direct. Instead, they require an intermediate host, a tiny mite that feeds on horse feces. There, the eggs develop for several months. Then, if another horse feeds on grass or hay contaminated with the mite, it becomes infected.

Adult tapeworms attach to the area where the small intestine terminates at the cecum. Infections in horses can lead to inflammation, ulcers, or a thickening of the tissue in this area. The damage caused might lead to obstruction or intestinal pain. Depending on the species of tapeworm, your vet might recommend giving pyrantel salts, equine dewormer paste, or both. These products are sometimes used to prevent tapeworm infections during the grazing season.

Small Stomach Worm – The small stomach worm, or hairworm, is found in horses and cattle. Usually, it is only a problem where horses and cows share a pasture. The larvae penetrate the stomach lining, producing a long-term bloody inflammation of the stomach. As a result, the infected horse might have weight loss and stomach ulcers. Diagnosis is difficult and may take longer than with other types of worms. Once diagnosed, the vet will advise you on which medication to use.

Strongyloides – Strongyloides westeri are found primarily in foals. Mares often have larva in their tissues that is activated during foaling. The larvae are then passed to the foals in their milk. Treating the mare with an equine dewormer within 24 hours of foaling will prevent the larvae from passing to the foals.

Ascarids – These parasites are thick, white-looking worms that grow up to 12 inches in length. Like Strongyloides, they primarily affect foals that become infected by ingesting the eggs. The Ascarids’ eggs can remain viable in the soil in the pasture or stalls for years. Signs of infections in foals include respiratory symptoms resembling those of summer colds. They can also show poor condition, have low energy, or have symptoms of colic.

An equine dewormer can be given if the foal is diagnosed early enough. This causes immature worms to pass in the feces.

If Ascarids are common on a farm, equine dewormer should be started when foals are about eight weeks of age, then repeated every six to eight weeks until they reach one year of age.

Horse Bots – These parasites aren’t really worms but the larvae of botflies that make their way through a horse’s mouth and into its stomach. There, they attach to the stomach lining, causing wounds, blockages, and ulceration. They are most likely to cause damage when present in large numbers. Some types of equine dewormer are effective during the oral and stomach stages of the larva.

Non-Chemical Parasite Management

There are some steps you can take to help prevent your horses from getting infected, including:

• Rotating pastures instead of using the same fields year after year
• Avoiding putting horses and cattle in the same pastures
• Removing manure from pastures and stalls regularly
• Avoiding over-stocking pastures
• Using different pastures or paddocks for mares and foals to avoid the build-up of Ascarid eggs

Even with these precautions, you should have your horses regularly tested, followed by any treatment indicated. 

Using Dewormer

Some equine dewormers come in pellets that you mix in with a horse’s feed. If some horses hesitate to eat the entire dosage at once, simply withhold grain for the next feeding to encourage full dosing. In general, most horses find the taste of these pellets palatable and eat them without much encouragement.

Most dewormers come in a paste. Some horses don’t mind the taste of the paste, while others will avoid it if possible. Hopefully, the first attempt will be a positive experience that won’t result in a repeat every year. Consider the following steps by horse expert Clinton Anderson.

Step 1: Desensitize the Air Space

Wave an empty syringe back and forth around his head. Once he holds his head still, stop, retreat, and rub his head with your other hand.

Step 2: Desensitize to the Syringe

Rub the syringe all over the horse’s face. Then, as he becomes increasingly desensitized, rub the dewormer down and around his muzzle.

Step 3: Coat the Syringe

Use something like honey or sugar. This will help your horse associate the sweet taste with the dewormer.

Step 4: Deworm with Honey

Fill an empty syringe with honey and rub it around the horse’s nose to desensitize him to it. Then, place it in the dewormer corner of his mouth and let him lick the honey off.

Step 5: Deworm Your Horse

Now that your horse accepts the deworming syringe, you can use the dewormer. After you successfully give the wormer, follow with a dose of honey.

Leaving your horse with a positive taste after deworming will help prevent him from fighting you when you repeat the treatment.

Use the Right Equine Dewormer for the Infection

Worming your horse without knowing which worms are causing the infection is ineffective and dangerous. Using the wrong dewormer won’t kill the parasites. Instead, it will allow them to continue growing. Always have your vet test your horse before applying treatment. Using too much wormer can result in resistance that makes your horse more susceptible to serious side effects from some infections.

If you need more information on using dewormers for your horse, contact Grange Co-op using our online question form. Our experts are happy to help you choose the best products to keep your horses happy and healthy.