Worm infestation in horses 

Prevention is better than cure! The infestation of worms is often underestimated by people, despite the fact that it can have serious consequences for a horse! Symptoms that may indicate a worm infestation include colic, diarrhoea, mouth ulcers, weight loss, and/or deteriorated condition. Depending on the type of worm and the extent of the infestation, the horse may even die if not acted upon in a timely manner. 

In fact, almost every horse has some form of worms present in their body. It is only when the worm infestation becomes significant and the worms occur in large numbers within the horse’s body that we refer to it as “a horse with worms” or “worm infestation”. Horses become infected with worms when they eat, drink, or lick, allowing them to ingest larvae that then search for their preferred spot in the body. Once the larvae develop into worms, they return to the gastrointestinal tract. These worms lay eggs in the intestines, which are then passed out with the feces, making it easy for other horses to become infected. Meanwhile, the adult worm will damage the intestinal wall, leading to bacterial infections, diarrhoea, and the presence of blood in the feces. 

Preventing infestation of horse worms

Most worm infestations occur in the pasture. Once you have an infestation in your pasture, it can take a long time to make it worm-free again. Therefore, proper pasture management is crucial. Here are some things you can do to maintain your pasture: 

• Remove manure regularly (at least once a week). 
• Keep the number of horses per area small (low stocking density). 
• Allow periods of rest for the pastures (rotational grazing). 
• Allow other animal species to graze the pasture. 
• Consider mowing the grass or making hay/silage. 

When you allow other animal species (such as sheep) to graze the pasture, they will eat the worms and help remove them from the grassland. Since worms are species-specific, horse worms will not infect sheep and vice versa. Another option is to mow the grassland, but be cautious that the larvae do not remain in the grass when you put the horses back. Using the pasture for making hay or silage also helps kill the worm larvae through drying or the acidification process. 

De-worming your horse

Although it is best to prevent infestation, there are times when it becomes necessary to de-worm your horse. However, this should be done with caution to avoid the development of resistance. To prevent resistance, there are several factors to consider: 

• Regularly conduct faecal egg count tests or worm tests on your horse (preferably for all horses at the same time). 
• De-worm only when necessary based on the results of the faecal egg count test. 
• Use the appropriate de-worming product for your horse. 
• De-worm at the right time. 
• Ensure correct dosing during de-worming; too much is generally not harmful, but too little can be ineffective. 
• It is often recommended to de-worm horses annually, preferably in November, with a product targeting tapeworms. 

Since your veterinarian has the proper knowledge about the effectiveness of different products, the appropriate dosage for your horse, and the right timing, it is important to consult with them. In cases of significant infestation, your veterinarian can prescribe a specific de-worming treatment. 

There is an exception to these guidelines for horses three years old and younger. Younger horses are more susceptible to worm infestations and may require more frequent monitoring and/or de-worming.