Constipation and Straining to Defecate 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.

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.

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

In some cases, toxins are the cause of constipation.

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

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.

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

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.