Deworming the horse

Worms can cause major problems in horses. Regular deworming is therefore of great importance. Unfortunately, resistance to deworming agents has developed significantly over the past decades. Deworming according to a standard schedule that is the same for every horse is outdated. Deworming is now done tailored to the individual horse and based on fecal testing. A worming treatment for horses is available only by prescription from your veterinarian, all to minimize the chance of resistance. Pharmacy4pets is happy to assist you, along with your veterinarian, in choosing the right deworming for your horse.

How do horses get infected with worms?

In horses, worms mainly live in the gastrointestinal tract. When a horse has worms, it passes worm eggs in its feces. If that feces remains in the pasture, the eggs develop into larvae, which are then ingested by the horse during grazing, thus repeating the cycle.

What problems do worms cause in horses?

Worms can be very dangerous for horses. Consequences of a worm infestation can include colic, diarrhea, gastric ulcers, anemia, coughing, weight loss, and stunted growth. Sometimes a worm infestation can even be fatal. Worms often cause serious problems, especially in young horses.

What types of worms occur in horses?

There are various types of worms that can occur in horses. We will briefly discuss the most common types of worms.

Pinworm

Even a few days after birth, foals can become infected with pinworms. Symptoms, especially diarrhea and weight loss, usually occur when they are a few weeks old. By a few months of age, foals usually have built up sufficient resistance to pinworms.

Roundworm

Roundworms are particularly dangerous for horses up to one year old. Roundworms make a whole journey through the body. The larvae also end up in the lungs, causing the foal to develop coughing or nasal discharge. If the foal coughs up and swallows the now mature larvae from the lungs, they end up in the intestines. If many adult roundworms are present at the same time, they can even cause intestinal obstruction, usually resulting in death. A roundworm infection can also cause lethargy, diarrhea, and weight loss.

Redworm

Redworms are common in young horses (between one and three years old). The larvae of the redworm remain in a resting stage in the mucous membrane of the large and small intestines for some time. When they emerge from the mucous membrane, usually in winter, they cause symptoms such as severe weight loss, poor coat, diarrhea, and colic. The risk of infection with redworms is greater when there are many young horses in the same pasture.

Large Strongyles

Fortunately, infections with large strongyles are less common nowadays. The larvae of the large strongyles migrate through the intestinal wall to the small blood vessels of the intestine towards a large artery. Due to damage to the blood supply to the intestine, large strongyles often cause severe colic, usually in young horses.

Tapeworm

Horses can become infected with tapeworms, especially in the fall. The tapeworm attaches itself to the intestinal wall and produces segments in which eggs develop. The segments are excreted with the feces and can be recognized as white flat pieces in the feces. By attaching to the intestine, tapeworms can cause inflammations that can lead to colic.

Pinworms

The pinworm or threadworm lives in the last part of the intestine and lays its eggs on the outside of the anus. This causes itching and tail rubbing.

Bots

Bots are not worms, but they are susceptible to the deworming agent ivermectin and should be considered in the deworming schedule. Especially in August, botflies lay eggs in the horse's coat. The botfly eggs are licked by the horse and remain in the mucous membrane of the mouth for the first few weeks, after which they migrate to the stomach as larvae and attach to the stomach wall. As a result of an infestation with bot larvae, horses can develop inflammations of the mouth, tongue, and stomach, and even stomach ulcers. Weight loss, anemia, diarrhea, and colic can also result from an infestation with an excessive number of bot larvae.

Which horses are most at risk of worms?

It is important for all horses to be dewormed regularly, but there are significant risks of worm infestation, especially in young horses and pregnant mares.

Horses aged three years and younger

Young horses are more likely to be infected with worms and often become more seriously ill from a worm infestation. Therefore, it is advisable to conduct fecal testing more frequently in these animals or to deworm according to a fixed schedule. Additionally, there is more resistance in foals, and not all deworming agents are suitable for young foals. Consult your veterinarian for appropriate advice.

Pregnant Mares

One to two weeks before the due date, pregnant mares should be dewormed with ivermectin. Additionally, the stable should be thoroughly cleaned and sanitized before birth to prevent infection of the newborn foal.

Deworming: How to Approach It?

Due to the prevalence of resistance, deworming is no longer done according to a standard schedule; instead, tailored deworming is advised for each horse. Research indicates that only twenty percent of horses shed too many worm eggs. If all horses in a group were dewormed simultaneously, many horses would be unnecessarily treated, fostering resistance and incurring unnecessary costs. Therefore, deworming should be based on fecal testing.

Fecal Testing

In fecal testing, the feces are examined for the presence of worm eggs. If there are too many worm eggs in the feces, depending on the type of worm, a deworming treatment is recommended. It is advised to perform fecal testing two to three times a year (in March, June, September) for horses aged three and above. For this, you should use the freshest possible feces that has not been in contact with the ground. In the fall and winter, fecal testing may yield false-negative results because some worms are then in a state of 'winter dormancy' and do not lay eggs. Therefore, it is recommended to deworm all horses in the fall with a deworming treatment that also works against tapeworms.

Types of Dewormers

Deworming treatments are mainly administered as paste and can be divided into four groups:

Benzimidazoles (febantel and fenbendazole), for example, Panacur.
Macrocyclic lactones (ivermectin and moxidectin), for example, Eraquell and Equest.
Tetrahydropyrimidines (pyrantel pamoate and pyrantel embonate), for example, Strongid-P.
Praziquantel is the only one (at a normal dosage) effective against tapeworms. To combat tapeworms, you can choose Noromectin Praziquantel Duo, in which two different dewormers are combined.

Attention! Deworming treatments are available only by prescription. Before ordering this veterinary medicinal product, you should be aware that you must send the original, physical prescription (even if it is a repeat prescription) to us by mail. Have you received a digital prescription? Then ask your veterinarian to send the original, digital prescription directly to us.

Preventing Resistance to Worm Infections

By deworming based on fecal testing, choosing the right deworming treatment, administering the correct dosage (based on body weight), and practicing good pasture management, resistance can be minimized. Good pasture management helps keep the risk of worm infection and, consequently, the use of dewormers low. Good pasture management consists of:

Removing manure from the pasture at least twice a week.
Regularly moving horses to a clean paddock. Fecal testing should be done before moving, and if necessary, deworming should be performed.
Alternating grazing areas by, for example, grazing with cows or sheep, or mowing the pasture in between.

If a new horse joins an existing group, fecal testing should be performed. By repeating fecal testing after deworming, it can be determined whether this new horse has resistant worms.

Worm infections are common and can cause serious problems, especially in foals and young horses. Due to the high prevalence of resistance, it is important to deworm 'tailored' to the individual. It is advised to have fecal testing performed two to three times a year in horses older than three years and to deworm all horses in the fall with a treatment that also works against tapeworms. By removing manure from the pasture at least twice a week, you significantly reduce the risk of worm infection and thus the need to deworm your horse. At Pharmacy4pets, you can obtain deworming treatments for your horse with a prescription from your veterinarian.

If you have any questions about our products or about worms in horses, please contact us.