Constipation and Straining to Defecate in Horses

Key Takeaways

Constipation in horses occurs when the process of eliminating feces from the digestive system is very slow or stops altogether. 

• Constipation is associated with tenesmus, which is the term for straining to defecate

• The main causes of constipation and tenesmus in horses include poor diet or lack of water, poor dental care, diseases or dysfunction of the digestive tract, toxicoses, and infection with parasites or other organisms

• Horses with constipation must not be fed until the symptom is resolved to avoid complications due to overloading the structures in the digestive tract

• Diagnosis involves a physical examination, nasogastric intubation, and rectal palpation

• Treatment depends on the underlying cause, including dietary changes, laxatives, fluid therapy, pain relief, deworming, and in severe cases, surgery

A Closer Look: What is Constipation in Horses?

The gastrointestinal system of the horse is both large and sensitive, and disruptions to it are common and concerning. Some causes of constipation are life-threatening if left untreated. Veterinary attention is required for horses who are having difficulty defecating. If constipation is accompanied by fever or severe signs of colic, emergency attention is required. 

Healthy horses pass several well-formed apple-sized fecal balls that do not carry a significantly unpleasant odor and are fairly uniform in color, between 6 and 16 times per day. 

The severity of constipation depends on whether any feces is getting through at all, how long the symptom lasts, and what other symptoms are present.

Mild constipation occurs when small amounts of dry feces are passing, or when defecation is less frequent than usual, or when struggling to defecate is apparent but some feces are still passing. Severe constipation occurs when no fecal matter is passing at all.

Note: Horses with constipation must not be fed until the problem is resolved to avoid overloading the structures in the digestive tract.

Possible Causes

There are many potential underlying conditions that result in constipation. The most important factors contributing to development of constipation in horses are how much water has been consumed and how much daily exercise is part of the lifestyle. Horses that do not have constant access to drinkable water are likely to develop constipation. Horses that do not get enough exercise often have difficulty defecating due to poor gut motility.

In some cases, constipation results from an impaction, where the material in the digestive system is too tough to be digested. This might result from the following:

• Improperly chewed food due to dental problems

• Improperly chewed food due to eating too quickly

• Indigestible foreign objects such as sand or twine

• Eating too much dry hay or other fibrous material

In some cases, a mechanical problem in the digestive system prevents proper processing of food, including:

Volvulus (the twisting of a structure around itself)

Strangulating lipomas, which wrap around a section of intestine


• Adhesions

Gastric dilation

Rupture or perforation


In some cases, constipation may occur due to an infection in the digestive system, including:

• Parasites, such as ascarid infection

• Bacterial infections, such as Clostridia

In some cases, toxins are the cause of constipation, including:

• Plants, such as oak or black locust toxicosis

• Minerals, such as arsenic

In some cases, underlying digestive diseases are the cause of constipation, including:

• Hyperlipidemia

• Cancer

• Cholangitis

Risk Factors

Factors that increase the risk of constipation and tenesmus in horses include:

• Age: older horses are at higher risk

• Changes in feed

• Inadequate access to drinking water

• Dental problems

• Intake of certain medications

• Eating foreign materials

• Eating too quickly

Horses that have difficulty defecating for a day or two require close monitoring. In cases where it has been several days without evidence of a bowel movement, or in cases where constipation is accompanied by signs of colic, immediate veterinary attention is required.

Testing and Diagnosis

Diagnostic tools include:

• Physical examination

• Rectal palpation

• Nasogastric intubation 

• Bloodwork

• Cultures to identify bacterial infections

• Fecal egg count for parasites

• Diagnostic imaging, such as ultrasound

Note: Nasogastric intubation should only be performed by a veterinarian. There is no safe way to intubate a horse at home.

Treatment depends on the underlying cause, and may include:

• Laxatives

• Fluid therapy 

• Antiparasitic medications

• Antibiotics

• Anti Inflammatories

• Pain medications

• Medications specific to underlying diseases

• Surgery

Similar symptoms

There is a wide variation in the amount and frequency of defecation in healthy horses depending on water intake and activity levels. It is possible to mistake normal changes in fecal output for constipation.

Associated Symptoms

Symptoms often observed with constipation include:

• Lethargy

Exercise intolerance

• Decreased appetite

• Mucous covering the manure

• Rough, dry coat

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