Worms In Horses Symptoms You Need To Know

Like other mammals, horses are subject to parasitic infestations. The list of worms affecting horses is long, but common types include large roundworms, pinworms, tapeworms, and even non-worm parasites like botflies. If you suspect worms in your horses, we’ve listed the primary symptoms below. Luckily, treatment is typically inexpensive and easy to administer! De-worming is a part of regular horse maintenance.

Worms in Horses Symptoms

New or light-load parasitic infestations often have no clinical signs. Specific worm varieties may have distinctive identifiers, but these are the primary symptoms of worms in horses:

  • Inflammation or ulcers in the stomach (seen with botflies)
  • Loss of condition, weight, or colic (seen with tapeworms)
  • Diarrhea, colic, anemia, or weight loss (large strongyles)
  • Loss of condition, colic, anemia, or malnutrition (small strongyles)
  • Evidence passing in fecal matter (visual inspection works)
Worms in Horses Symptoms

Worms can also affect growth rate in young horses and overall nutrition in both foals and mature horses. Some horses will develop a “wormy belly”, which also falls under the loss of conditioning. The belly may seem round and pronounced, yet ribs may still be visible and weight is harder to maintain. Just like a “potbelly” appearance in puppies with worms, horses will look imbalanced and unusually round through the barrel.


New and low infections may not cause immediate noticeable problems in horses. However, worms can quickly progress and damage your horse’s coat, condition, and overall health. Colic is one of the major effects of parasites. Weight can be very difficult to maintain, if at all, with a high presence of worms feeding on your horse. Anemia is frequently caused by large strongyles, or “red worms”. Larvae damage blood vessels creating ulcerated nodules while mature worms leave exposed “holes” in the intestinal mucus lining. This can lead to infection or bleeding ulcers. Worms not having negative effects on horses is a common misconception. Research has shown parasites do far more damage than what meets the eye, especially if left untreated.


Equine dewormers are used to treat any parasitic infestations. However, only certain dewormers will have an effect on specific types of worms. Treatment is largely dependent upon your horse’s day-to-day risk factor and advisory from your equine veterinarian. The American Association of Equine Practitioners has created an internal parasite guideline you can find here. However, you and your vet can discuss creating a deworming schedule that works for you as each horse is unique. Some owners will have fecal tests performed and only treat active infestations. However, there are some recommended guidelines all owners should follow such as treating after the first frost. Because deworming can affect the pH balance of the digestive system, it is recommended to follow up de-worming with probiotics. Dewormers can be classified as:

  • Benzimidazoles
  • Pyrantel
  • Macrocyclic lactones (such as Ivermectin)
  • Praziquantel

Be sure to pay attention to dosing. Although multiple deworming compounds may be used to treat the same parasite, dosages may differ for effectiveness. Dewormers are also available in flavored easy-to-administer oral pasts.

Probios Dispersible Powder


The best way to prevent worms is to break the annual cycle. Unfortunately, pasture access frequently results in horses accidentally ingesting parasites. The environmental controls include picking up manure and not spreading manure in grazing areas.

Final Thoughts

Internal parasites are simply a part of owning a horse or other pets. But with attentive horse care and knowledge of deworming, they can be easily managed.

Speaking of the first frost, it is around the corner in many areas! Be sure to share this article with your friends.

Related Posts