Worms can be managed effectively by being on a worming program, faecal egg counts are also very useful. You can contact your vet for more information. Using alternate wormers to cover the type of worm for the season as there have been studies of worms growing immunity to wormers if used often.

Careful management especially for horses turned out at grass when worming. Horses should be kept in for the recommended amount of time after worming to avoid the spread to other horses.

Horses can contract many different types of worms and if left unmanaged they can be life threatening. Worms most commonly affecting horses are particularly dangerous as they can cause extreme weight loss, colic, stunted growth and even lead to death, a worm burden is very serious and for the welfare of our horses we should ensure we worm them as required.

 Large red worm

these are the most dangerous of worms which affect horses. Adults eat the lining of the gut wall, causing bleeding and damage. Larvae burrow through the gut wall into the bloodstream and travel around the body to other organs. They can cause Blood clots and weakening of the blood vessel walls this can cause arteries to burst under increased pressure and will kill the horse. 

Small red worm

 if untreated these cause severe damage to the gut leading again to weight loss, runs and colic. These burrow into the gut wall, where they remain during the winter months before reappearing in the spring. The reappearance of large numbers at once will lead to severe damage. 

Round worm

Roundworm larvae can cause lung and liver damage and damage to the digestive system. Worm numbers can build up very quickly and may result in a blockage or rupture of the gut.

Pinworms/red worms

 Thread worm live in the large intestine.  pinworms damage the bowel and symptoms can be itching around the tail, it can become that extreme that horses cause open wounds from the itching. Intestinal threadworms are often dormant in adult horses but transfer to a newborn foal via a mare’s milk, leaving the foal weak and affecting the foals growth.


Tapeworms cause less direct internal damage to a horse’s intestine but large numbers can cause a blockage, particularly as they tend to congregate at the narrow area where the small and large intestines join (illeocaecal junction). They may also cause stomach upsets and cause colic. 

Bot eggs/worms

Bots are larvae from flies otherwise known as bot flies. They are especially common in the summer. Horse bot flies lay their eggs in the horse’s coat and as the horse grooms by licking, the eggs are ingested. Upon entering the horse’s mouth, the eggs hatch into larvae which then travel down to the stomach. If they are left untreated the horse can suffer inflammation in the mouth and throat and ulceration of the stomach. A Heavy burden of these parasites can cause colic.