Parasitism (Gastrointestinal) in Horses

Parasitism (Gastrointestinal) in Horses - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost
Parasitism (Gastrointestinal) in Horses - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost

What is Parasitism (Gastrointestinal)?

These parasites can cause internal damage leading to gastrointestinal and cardiovascular trauma, colic, and in some cases thrombosis. Once internal damage has been caused by parasites the prognosis may be guarded, therefore, it is essential that an effective parasite control program is put in place with your veterinarian.

There are over 150 species of internal worms that may affect horses. Although many horses, even with severe worm burdens may appear healthy, others may suffer from diarrhea, chronic coughing, lack of appetite and weight loss.

Symptoms of Parasitism (Gastrointestinal) in Horses

The symptoms your horse experiences may vary greatly depending on the type of worm infestation they are suffering from. Often, the symptoms are caused by the migration of the worms in the larval stage. The most common symptom is diarrhea leading to weight loss and shock. 

  • Depression and reduced appetite 
  • Bloating
  • Coughing 
  • Increased heart rate 
  • Dehydration (signs include increased skin tenting, sunken eyes, reduced perspiration)


Causes of Parasitism (Gastrointestinal) in Horses

Small Strongyles or Red Worm (Cyathostomin spp)

These are the most common parasites in horses which can cause severe damage to the intestinal wall of the horse. Symptoms of infection can include diarrhea, leading to weight loss and shock. If the horse suffers from intestinal wall damage the prognosis is unfortunately poor, in over 50% of cases of horses with intestinal wall damage treatment is unsuccessful. 

Large Strongyles 

These worms, including strongylus edentatus, S. vulgaris, and Triodontophorus spp. are becoming increasingly uncommon due to successful worm treatment protocols. Symptoms of infection include reduced appetite, weight loss, and poor performance. The larvae of these worms can cause severe damage to the body during migration such as thrombosis and loss of blood supply to the intestines, the rupture of blood vessels or the intestine, and in some cases death. 


This worm is most commonly found in young and older horses. Complications caused by infection are ulceration of the intestinal wall leading to colic and obstruction or rupture of the intestine. 


Most commonly affects young horses with immature immunity. As the larvae migrate through the liver and lungs they may cause coughing and nasal discharge. Adult roundworms live in the intestine and may cause bloating, colic, intestinal blockage or death. 


These are small, uncommon worms that reside in the lower intestine of the horse. As they lay their eggs around the anus they can cause irritation, leading to itching and self trauma. 

Other less common worms include the following. 

  • Lungworms which can cause chronic coughing due to larval migration to the lungs
  • Stomach worms 
  • Neck threadworms which live in the tendons and ligaments of horses
  • Stomach hairworms which reside in the stomach and may cause damage to the stomach lining


Diagnosis of Parasitism (Gastrointestinal) in Horses

Your veterinarian will carefully examine your horse, performing a “head to tail” examination. During this time, they will carefully listen to the heart, lungs and gastrointestinal tract. Your veterinarian will discuss the clinical history of your horse with you, including recent vaccinations or travel of late.

Your veterinarian may choose to send a sample for a fecal egg count. This will be performed by sending manure balls from your horse to a laboratory to be tested. This microscopic examination counts the eggs present per gram of manure and determines light, medium or heavy parasitic load. This also allows identification of the worms present.



Treatment of Parasitism (Gastrointestinal) in Horses

The ideal treatment medications and timing vary for different species of worms in horses. For example, red worm treatment should be given during winter. The only effective treatments are moxidectin and fenbendazole. For large strongyles, the treatment is with any ivermectin based wormer, while tapeworm should be treated with wormers containing pyrantel or praziquantel. Roundworm treatment is done by administering ivermectin or fenbendazole wormers. Additionally, pinworm treatment is usually with ivermectin based wormers, however, resistance is forming in this species. To counteract this, weekly or rectal worming may be beneficial.



Worried about the cost of Parasitism Gastrointestinal treatment?

Pet Insurance covers the cost of many common pet health conditions. Prepare for the unexpected by getting a quote from top pet insurance providers.

Recovery of Parasitism (Gastrointestinal) in Horses

For horses that are provided with regular deworming treatment the prognosis is good; unfortunately, for horses with large burdens who have suffered from severe internal damage the prognosis may be guarded. 

For long-term management you should discuss a deworming program with your veterinarian including regular fecal egg counts to monitor parasite burden. 

However, as well as chemical control other steps should be put in place to reduce the parasite burden for your horse. 

  • Regularly muck out stables and dispose of manure
  • Compost manure in an area away from horse grazing 
  • If possible, allow sheep or cattle to graze on paddocks following horses to interrupt the life cycles of equine parasites
  • Use feeders for hay and grain

Further steps of supportive care you can offer your horse if they are suffering from diarrhea are:

  • Braiding your horse’s tail to reduce fluid on the hair 
  • Apply ointment to prevent or reduce scalding
  • Gently clean your horse’s hindquarters with warm water
  • Reduce stress
  • Feed a good quality, constant diet of top quality hay or weed free pasture to support gut health


Parasitism (Gastrointestinal) Questions and Advice from Veterinary Professionals

Need pet insurance?
Need pet insurance?

Learn more in the Wag! app

Five starsFive starsFive starsFive starsFive stars

43k+ reviews


© 2022 Wag Labs, Inc. All rights reserved.