Prevalent Parasites: Common Types of Equine Internal Parasites

As responsible horse owners, it is crucial to understand the various types of internal parasites that can affect our equine companions. These pesky parasites cause discomfort and health issues for our horses and can impact their overall well-being and performance. In this article, we will explore some of the most prevalent parasites found in horses and discuss the importance of implementing a proactive parasite control program.

1. Small Strongyles (Cyathostomins)

Small strongyles, also known as cyathostomins, are one of the horses’ most common internal parasites. These tiny worms inhabit the large intestine and can cause various health problems, including weight loss, diarrhea, and colic. Younger horses are particularly susceptible to small strongyles, as they have not yet developed immunity against the parasites.

To control small strongyles, veterinarians recommend implementing a strategic deworming program targeting adult worms and their encysted larvae. Rotating the deworming medications used to prevent resistance from developing in the parasite population is crucial.

2. Large Strongyles (Strongylus spp.)

Large strongyles, or Strongylus worms, are another common internal parasite affecting horses. These worms primarily target the large intestine and can cause severe damage to the blood vessels, leading to colic and even death in extreme cases.

Preventing large strongyle infestations involves regular deworming and maintaining a clean environment to minimize exposure to infective larvae. Horses should also be kept from pastures grazed by infected animals or have a history of strongyle infestations.

3. Roundworms (Parascaris quorum)

Roundworms, scientifically known as Parascaris equorum, are primarily a concern in young horses, particularly foals. These worms can grow up to 15 inches long and inhabit the small intestine. Infestations can lead to poor growth, weight loss, and in severe cases, intestinal blockage.

As per a veterinarian’s recommendation, regular deworming of young horses is essential to control and prevent roundworm infestations. Additionally, practicing good hygiene in the stable and paddock areas by removing feces promptly can help reduce the risk of transmission.

4. Pinworms (Oxyuris equi)

Pinworms, or Oxyuris equi, are tiny worms that inhabit the large intestine and rectum of horses. While their presence may not cause significant health problems, pinworm infestations can cause intense itching and irritation around the horse’s anus, leading to tail rubbing and hair loss.

Regular deworming and measures to prevent reinfection are crucial to control pinworms. Thoroughly cleaning and disinfecting stable and grooming equipment can minimize the risk of contamination.

5. Tapeworms (Anoplocephala spp.)

Tapeworms are flat, segmented worms that attach to the walls of the horse’s intestines. While they are less prevalent than other internal parasites, tapeworm infestations can cause colic and other digestive issues.

Regular deworming is essential to control tapeworms, but it is important to note that standard dewormers may not effectively eliminate them. As a veterinarian prescribes, specific dewormers targeting tapeworms should be used to ensure effective treatment.

6. Bots (Gasterophilus spp.)

Bots are the larvae of Gasterophilus flies and are unique among equine parasites as they inhabit the stomach rather than the intestines. These larvae can attach themselves to the stomach lining and cause irritation and ulcers.

To control bot infestations, regular deworming treatments should be complemented with targeted measures to eliminate bot eggs. Specialized bot knives or grooming tools can remove bot eggs from the horse’s coat before ingesting them.


Understanding the various internal parasites that can affect horses is crucial for every horse owner. By staying informed about prevalent parasites and implementing a proactive and strategic deworming program, we can help ensure our equine companions lead healthy and parasite-free lives.

Leave a Reply