The small strongyle, also known as Cyathostominea, is one of the most common types of worms 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 strongyle (Strongylus). This worm grows to between 1 and 5 centimeters long, but it is rare in the Netherlands.

How does a horse get infected with strongyles?

The life cycle of the large and small strongyle is largely similar:
1. A horse becomes infected when it ingests the larvae of the red strongyle while grazing.
2. The larvae embed themselves in the mucous membrane of the cecum and large intestine and can overwinter there for several months. The larvae of the large strongyle can migrate further to the large arteries, where they can cause a lot of damage. They then return to the intestinal mucosa.
3. Once the larvae have become adult worms, they start producing eggs. Only uncapsulated worms excrete eggs.
4. Approximately five to six weeks after infection, the eggs are in the feces. This can take longer in winter.
5. The feces containing the strongyle eggs then end up back in the pasture, after which the eggs can infect another horse. A horse can only become infected if the eggs have developed into larvae. If the larvae are not ingested by a horse, they can survive in the pasture for several months.

Source: Corning S. Equine cyathostomins: a review of biology, clinical significance and therapy. Parasit Vectors. 2009; 2(Suppl 2): S1

Strongyles in horses - symptoms

Strongyles in horses can cause various symptoms. In a mild infection, a horse may show no symptoms. The horse then appears healthy but can still infect other horses. Common symptoms include weight loss, reduced appetite, and a dull coat. Ataxia, fever due to an accompanying infection, diarrhea, anemia, and colic are also seen. A severe infection can be fatal for the horse or cause permanent damage. Permanent damage can lead to chronic colic, reduced performance, and difficulty maintaining the horse's weight.

Controlling strongyles in horses

To investigate whether the horse has strongyles, a fecal examination can be performed. This involves looking for worm eggs in the feces. The worm eggs of the large strongyle and small strongyle cannot be distinguished. Therefore, the total number of eggs is stated in the results. It is important to note that larvae can be encapsulated, meaning that even with a negative result, there is still a possibility that the horse is infected. When a horse is infected with strongyles, deworming treatment can be given. Depending on the severity of the infection, the type of veterinary medicinal product to be used may vary. Because a lot of resistance to the active substance is seen with deworming treatments, it is advisable to have a fecal examination done approximately two weeks after administering the deworming treatment.

Preventing strongyles in horses

To prevent strongyle infection, there are various measures you can take. You can try to keep the contamination of your pasture as low as possible by cleaning up manure (at least twice a week). In addition, you can regularly harrow the pasture, clean and disinfect the stable, use strip grazing, and perform periodic fecal examinations. This way, an incipient infection can be detected in time and further spread can be limited as much as possible.