Bloodworm in Horses

The small bloodworm, also known as Cyathostominea, is one of the most common types of worms found in horses. These worms are about 0.5 to 3 centimeters long and are mainly seen in young horses up to three years old. A horse can also become infected with the large bloodworm (Strongylus). This worm measures between 1 and 5 centimeters, but it is rarely found in the Netherlands.

How does a horse become infected with bloodworm?

The life cycle of the large and small bloodworm is largely the same:

1. A horse becomes infected when it ingests larvae of the red bloodworm while grazing.
2. The larvae settle in the mucous membrane of the caecum and large intestine, where they can overwinter for several months. The larvae of the large bloodworm can migrate further into the large arteries, where they can cause significant damage. They later return to the intestinal mucosa.
3. Once the larvae have developed into adult worms, they start producing eggs. Only non-encysted worms shed eggs.
4. About five to six weeks after infection, the eggs appear in the manure. In winter, this process may take longer.
5. The manure containing the bloodworm eggs ends up in the pasture again, allowing the eggs to infect other horses. A horse can only become infected when the eggs have developed into larvae. If the larvae are not ingested by a horse, they can survive in the pasture for several months.

Bloodworm in horses – symptoms

Bloodworm infections in horses can cause various symptoms. In cases of mild infection, a horse may show no signs of illness. The horse appears healthy but can still infect others. Common symptoms include weight loss, reduced appetite, and a dull coat. Weakness, fever due to secondary infection, diarrhea, anemia, and colic may also occur. A severe infection can be fatal or cause lasting damage. Permanent damage can lead to chronic colic, reduced performance, and difficulty maintaining weight.

Treating bloodworm in horses

To determine whether a horse has bloodworms, a fecal examination can be performed. This test looks for worm eggs in the manure. The eggs of the large and small bloodworm cannot be distinguished, so the result reports the total number of eggs. It is important to note that larvae can be encysted, which means that even with a negative test result, infection may still be present. When a horse is infected with bloodworm, a deworming treatment can be administered. The type of medication depends on the severity of the infection. Because resistance to active ingredients in dewormers is common, it is advisable to perform a follow-up fecal test about two weeks after treatment.

Preventing bloodworm in horses

There are several measures you can take to prevent bloodworm infection. You can keep contamination of your pasture as low as possible by removing manure at least twice a week. In addition, regularly harrow the pasture, clean and disinfect the stable, use strip grazing, and perform periodic fecal tests. This allows early detection of infections and helps prevent further spread as much as possible.