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Worms in your horse: many species and sizes

Horses can carry different types of parasitic worms. Most of these parasites cause problems in the intestinal tract. But there are also worms that settle in the stomach. We have listed the most important types of worms for you and give you a few tips on prevention. All types of worms have their own life cycle. That cycle also determines how a horse ingests the parasites and how best to combat them. Usually it goes like this: A horse's manure can contain worm eggs. These eggs develop into small larvae in the manure. When your horse grazes near this manure, these highly contagious larvae can be ingested. The eaten larvae pass through the body to places where they nest. Sometimes that is in the intestinal wall, sometimes in the stomach. The larvae then grow into worms. Adult worms lay eggs again, which eventually come out through your horse's manure. And then the cycle starts again. Worm eggs and larvae can survive for a longer period of time on moist soil.

Red bloodworm

One of the best-known parasites in horses is the red bloodworm, or small strongylid. This is common in young horses, but can also infect older horses. For example, if an older horse is in the paddock with younger animals. They are small, thin, red worms that you sometimes find in the manure. Red bloodworm is mainly in the large intestine and can cause damage and, in severe cases, colic.


Roundworms are also mainly found in young animals. Especially in foals and yearlings. They are very large, fat white worms. Foals must be treated against it regularly with a special worm cure, otherwise roundworms can cause major problems. They start in the intestines, but can also damage the lungs and liver, for example. In the intestines, the large worms can cause a blockage and colic. That is why, together with the special worm cure against these worms, paraffin oil is sometimes given to infected horses. This way, the manure with worms comes out of the intestines more easily and there is no blockage.


The tapeworm is not super common, but it is a bit 'sneaky'. This worm is not found in manure research. Tapeworms grow very long. They can bite into the intestine and cause colic there. You can only fight tapeworm with a broad spectrum worm cure. Nowadays there is a saliva test for tapeworm, so you can see if your horse is infected.


Hornets lay eggs in the coat of horses, especially when they are out in the pasture. These eggs (appearing as small white-yellow dots) are then eaten by horses when they scratch themselves with their mouths. Or the eggs are absorbed by other horses, if they tickle each other. The hornet larvae then develop in the horse's stomach. That happens in the fall. Because the hornet larvae bite into the stomach wall, this can cause stomach damage. Many people therefore deworm against hornets in the course of the autumn.


Unlike many other parasites, pinworms are often in your horse with only one or a few copies at a time. You can recognize that your horse has an ass maggot by chafing the tail. The pinworm lays eggs around the anus of the horse and that itches enormously. It is important to treat a pinworm properly according to a special treatment schedule. Otherwise the pinworms keep coming back.

Stomach worm

Habronema worms are still relatively unknown in the Netherlands, but it seems that they have become more common lately. They have a somewhat complicated life cycle. The worms live in the horse's stomach and excrete their eggs with the manure. Fly eggs are also laid on that dung, which grow into maggots. The Habronema larvae that have also hatched in the manure then infect the maggots of the flies. After these maggots have grown into adult flies, they can deposit the Habronema larvae on moist spots on the horse's body, such as wounds or mucous membranes. Only larvae that are deposited in or around the mouth are swallowed and can complete their life cycle. You can see that your horse is infected with these larvae, because small round wounds appear on the lip. Contact your vet if you see these, the Habronema worms can be controlled with ivermectin or moxidectin.

Prevention of worms

Preventing a worm infestation is of course better than fighting it. The best way to combat red bloodworm, tapeworm and roundworm is to keep the pasture and paddock clean and to graze your horses regularly to give the country a rest. The eggs and larvae then disappear from the soil. The longer (contaminated) manure remains, the greater the chance of spreading a worm infection. To prevent hornet infections, you can remove the eggs from your horse's coat, for example with a pumice stone. And the Habronema worms are best controlled by avoiding contact with flies, for example by putting on a fly cap. In addition, it is wise to have a manure test carried out several times a year.

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