Den Hoek

Parasites in horses

Nematodes or roundworms are the most common parasites in the horse. Of these, the small strongyles (Cyathostominae), or “red bloodworm”, are the most common worm species in the horse.

Below is an explanation of the various worm types:

  • Small strongyles or small / red bloodworms (Cyathostominae): in the large intestine and caecum. The larvae burrow into the intestinal wall. If the larvae emerge en masse from the intestinal wall, it can be fatal to the host.
  • Large strongyles or large blood worms (Strongylus): the larvae migrate through the horse’s bloodstream. Adult worms live in the colon and appendix.
  • Pinworms (Oxyuris): live in the colon. Adult worms migrate to the rectum and lay their eggs there.
  • Roundworms (Parascaris): the larvae migrate through the horse’s bloodstream to the liver and lungs. Adult worms live in the small intestine.
  • Hairworms (Trichostrongylus): are located in the stomach.
  • Stomach worms (Habronema): are located in the stomach. The larvae occur in skin wounds and hinder their healing.
  • Foal worm (Strongyloides): the larvae migrate through the lungs. Adult worms live in the small intestine.
  • Onchocerca: skin.
  • Lungworm (Dictyocaulus): in the lungs. Infection via donkeys.

Fight worms

It is important to control worms properly. There are a number of available dewormers that can be used to combat worm infections. Because more and more resistance has developed against these products, it is important to only start deworming when necessary.

There are measures that can be taken to slow down the build-up of resistance:

  • Correct dosage: make sure there is no underdosing.
  • Avoid introduction of resistant worms: When introducing a new horse to the farm during the quarantine period, check the manure for the presence of worm eggs before and after treatment.
  • Treat less frequently: each treatment is a selection for resistance. The number of treatments should therefore be limited as much as possible. Only deworm when the manure research gives reason to do so and deworm directed against the worm species found.
  • Targeted selective treatment: adult horses generally excrete few or even no worm eggs and often do so consistently for the rest of their lives. These horses therefore hardly contribute to pasture contamination and therefore do not need to be dewormed.
  • Regular grazing: in dry summer weather, worm larvae survive only a few months, while in a mild winter the larvae can survive for more than 6 months.
  • Pasture hygiene: regularly (1-2 times a week) remove the manure from the pasture. This removes part of the potential meadow contamination, which means that deworming is much less frequent or even eliminated. Please note, it may be that the pasture was already contaminated before you started taking this measure.

Manure research

We recommend deworming based on manure research. This way it can be determined whether there is an infection and  with which parasite and to what extent. Based on this, it can be examined whether deworming is necessary, in addition, the correct product can best be determined in this way. Read more about the manure research for worm egg counting that you can have at our practice.

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