Worms In Horses Symptoms You Need To Know

Last Updated on February 1, 2022

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.

Can worming your horse cause colic?

Worming a horse sometimes can result in the impaction colic due to large amounts of worms killed by the wormer. When the amount of dead worms is big enough they can form an obstruction within the small intestine, leading to impaction colic. This is most common in young horses or those that haven’t been de-wormed for a longer period of time.
Symptoms include loss of appetite, weight loss, diarrhea, blood in the feces, and colic. Causes The most common cause of impaction colic in horses is the ingestion of undigested food. The second most common cause is a lack of exercise.

How do you test a horse for worms?

The best way to examine a horse for worms is to have a veterinarian perform a complete gastrointestinal tract examination. However, this is not practical for most horse owners.
A more common way to examine a horse for worms is to take a fecal sample and send it to a lab for testing. Most equine veterinarians recommend that the horse owner collect two or three fresh stool samples. The horse owner should keep the samples in a cooler with ice packs until they are delivered to the laboratory.

Can worms in horses cause pain?

If a horse is infested with pin worms, they are found in the feces (stool). Pin worms are known for causing the horse irritation and discomfort. The adult worms live in the horse’s colon. The females migrate to the anus and surrounding area where they lay their eggs.
Pin worms can be easily detected by looking at the feces of your horse. If you find pinworms in the feces, you need to treat them immediately. The treatment is an oral medication that kills the worm. You should consult your veterinarian before treating your horse with any medication. 

How do worms affect horses?

Compared to humans, horses have an immune system that is far less efficient at fighting off bacterial and viral infections. They can be exposed to germs from the environment, and even the parasites that infect them. Worms and their eggs can also be spread from horses to horses, which can cause a disease called equine parasitic gastroenteritis.
Equine parasitic gastroenteritis is one of the most common infectious diseases of horses. It is caused by a number of different parasites, including hookworms, roundworms, and tapeworms. The most common symptoms are loss of appetite, diarrhea, weight loss, and a bloated belly. The disease can be fatal if left untreated.

How do you tell if a horse needs to be dewormed?

Deworming isn’t a one-time event. It’s a regular part of keeping your horse healthy and parasite-free. It’s also important to keep in mind that horses can get parasites from other sources besides their environment. You can help keep your horse healthy and parasite-free by learning about parasites, their lifecycle, and how to recognize them. This will help you know when your horse needs deworming. Common signs a horse needs worming are weight loss, diarrhea, fatigue, itchy rear-end, and an off-color or unhealthy coat.