Constipation in Horses & Straining to Defecate (Tenesmus): Signs, Causes & Treatments

Regular bowel movements are essential for a healthy digestive system, ensuring waste is efficiently expelled from the body. In horses, irregular bowel movements pose a significant risk of life-threatening colic. 

When the stomach and intestines are not functioning optimally, or if feed is indigestible, feces can accumulate in sections of the intestine, leading to constipation or difficulty in defecation. If left unresolved, constipation can develop into impaction or bowel obstruction, a critical condition requiring urgent veterinary attention.

In cases of equine constipation, horses often struggle to pass manure, leading to hard, dry feces or a noticeable reduction in the frequency of defecation. ^[1] Constipation can result from inadequate water intake, poor diet, lack of exercise, or underlying health issues.

Constipation in horses requires prompt veterinary assessment since prolonged or severe cases can lead to serious complications, including colic. Understanding the causes, symptoms, and prevention strategies can help horse owners maintain their horses’ digestive health and overall well-being.

Signs of Constipation in Horses

Constipation in horses occurs when there is difficulty in passing manure due to slow or impaired movement of digested material through the intestines.

Recognizing constipation in horses involves observing various physical and behavioral signs. Key indicators include: ^[1][2][3][4]

• Tenesmus (straining): This is characterized by the horse straining to defecate despite producing little or no feces. The horse may exhibit repeated, forceful attempts to pass manure, which can cause discomfort and distress. Tenesmus often indicates irritation or obstruction in the rectum or lower gastrointestinal tract.
• Reduced Fecal Output: A noticeable decrease in the amount or frequency of manure passed is a common sign of constipation. The horse may produce less manure than usual or have fewer bowel movements per day.
• Abdominal Discomfort: Horses with constipation often show signs of abdominal pain (colic), such as restlessness, kicking at the belly, or shifting weight. This discomfort is due to the buildup of feces and pressure within the intestines, which can cause the horse to appear uneasy or agitated.
• Distended Abdomen: Swelling or bloating of the abdomen can occur as a result of fecal accumulation. The abdomen may appear enlarged and tense, which is a visible sign of gastrointestinal distress and may indicate an obstruction or severe constipation.
• Frequent lying down: The horse may lie down more frequently than usual as a response to abdominal pain or discomfort. This behavior, often seen as an attempt to find relief, can be accompanied by periods of restlessness or getting up and lying down repeatedly.
• Reduced Appetite: A decrease in a horse’s interest in food or reluctance to eat can be a sign of constipation.

Common Causes of Constipation

Constipation in horses can result from a variety of factors impacting digestive health. Understanding these causes is essential for effective prevention and management.

Inadequate Water Intake

Insufficient water consumption is a common cause of constipation in horses. In the digestive tract, water softens feces, facilitating its passage through the intestines. When horses do not drink enough, their feces can become dry and hard, making it difficult to pass. ^[5]

Dehydration results from insufficient water intake, particularly in hot weather or during periods of heavy exercise, or from conditions that increase water loss, such as diarrhea or sweating. ^[6][7]

To prevent constipation from inadequate water intake, ensure horses always have access to clean, fresh water. Monitoring water consumption and encouraging hydration, especially in hot weather or after exercise, helps maintain digestive health and reduces the risk of constipation. ^[2]

Poor Quality Roughage

Late-harvested hay tends to be overly mature and coarse, containing higher levels of lignin, a fibrous component that horses struggle to digest. This can result in large, undigested particles accumulating in the intestines, increasing the risk of digestive issues. ^[8][9]

Feeding horses poorly digestible feed, especially when it is low in quality or lacks sufficient moisture, is a common cause of equine constipation.

When feed is excessively fibrous and dry, it becomes even harder for the intestines to process and move along. This results in the accumulation of dry, dense material in the gut, which can obstruct the normal flow of digested content and lead to impaction.

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Dental Issues

Inadequate chewing is a significant cause of constipation in horses because it disrupts the initial breakdown of feed. Proper chewing reduces feed to smaller particles and mixes it with saliva, facilitating proper digestion. ^[10]

When horses fail to chew adequately, often due to dental issues like uneven wear or missing teeth, larger, unchewed particles enter the digestive tract. These particles are harder to process, leading to blockages and slower transit times, which can cause impaction. ^[2][4][11]

Lack of Exercise or Turnout

Regular physical activity helps stimulate the muscles of the digestive tract, ensuring efficient movement of food and waste through the intestines. When horses do not exercise enoungh, these muscles can become sluggish, slowing down gut motility and increasing the risk of impactions.

A sudden decrease in exercise, such as due to a musculoskeletal injury or stall rest, is closely associated with the development of impaction. Horses confined to stalls or not regularly turned out are particularly susceptible, as reduced movement can cause feed material to accumulate in the intestines, increasing the risk of impaction. ^[5][12]

Rectal Tear

A rectal tear is a serious injury in horses involving a tear or rupture in the rectum, the final section of the gastrointestinal tract where feces is stored until defecation. These tears can range in severity from superficial damage to deep, extensive tears that may affect surrounding tissues. ^[13]

When a rectal tear occurs, it typically results in significant pain and discomfort, which can make it difficult for the horse to pass manure. This pain may cause the horse to strain excessively or even avoid defecation altogether.

Additionally, the injury can lead to inflammation and swelling in the rectal area, creating a partial obstruction that impedes the passage of feces through the intestine. The horse may start associating defecation with pain, leading to reluctance to pass manure and worsening constipation.^[14]

Trauma, Tumours or Surgery

The horse’s gastrointestinal tract can narrow due to trauma, tumors, or previous surgery, restricting the normal flow of feed material. ^[4]

Trauma from injury or severe inflammation can cause scarring that reduces the intestinal space, impeding digestion. Tumours, or neoplasia, may develop within or near the intestines, blocking or compressing them. ^[15]

Surgeries on the gastrointestinal tract can lead to scar tissue or adhesions, bands of fibrous tissue that form between internal organs or the abdominal wall after surgery, which narrow the intestines.

These narrowed areas can create blockages, leading to impaction. Horses with these conditions may face ongoing digestive issues, requiring careful monitoring, dietary adjustments, and sometimes further surgical intervention.

Other Potential Causes

Other possible causes of equine constipation include: ^{[4][16][17][18]}

• Foreign Materials: Ingested foreign objects can cause physical blockages in the gastrointestinal tract, leading to constipation. Materials may include bailing twine, hay nets, bedding, sand, or fibers from feed sacks.
• Pain After Foaling: After foaling, mares often experience abdominal and pelvic pain, which can reduce their willingness to defecate. This discomfort can lead to straining or reluctance to pass manure, contributing to constipation.
• Medications: Certain medications can affect intestinal motility and contribute to constipation.
• Not Eating: When horses do not eat enough, their digestive system may lack the necessary bulk to stimulate normal bowel movements.

Impaction Colic

Impaction colic is closely linked to constipation in horses, occurring when a blockage forms in the intestines due to the buildup of feed material, sand, or other indigestible substances. Blockages disrupts the normal passage of digestive contents, leading to significant pain and discomfort. ^[6]

Horses suffering from impaction colic typically show signs of abdominal pain, such as pawing, rolling, or frequently lying down. They may also exhibit reduced manure production, reluctance to eat, or changes in behavior. ^[4]

If left untreated, impaction colic can lead to severe complications, including intestinal damage or rupture, making it a potentially life-threatening condition. The risk of a horse developing constipation or impaction can be greatly minimized with proper management. ^[4]

Treatment

Effective treatment for constipation in horses involves a multifaceted approach depending on the severity of the condition and the needs of the horse. Promptly addressing constipation offers the best chance of preventing complications like impaction colic.

Fluid Therapy

Administering fluids is a primary treatment for constipation. Fluids and electrolytes can be given orally, intravenously (IV) or through a nasogastric tube to help rehydrate the horse and soften the fecal material in the intestines. ^[4]

Rehydration is essential for restoring proper bowel function and easing the passage of impacted material. Fluid therapy also helps maintain hydration and electrolyte balance, which is critical for normal gastrointestinal motility. ^[19]

Laxatives and Stool Softeners

Laxatives and stool softeners are used to facilitate the movement of fecal material through the intestines. Common laxatives include mineral oil, which lubricates the intestines and helps to break down the impacted material, and magnesium sulfate (Epsom salts), which draw water into the intestines to soften the feces. ^[4][12]

These medications are typically administered via a nasogastric tube for effective delivery and rapid action.

Dietary Adjustments

Modifying the horse’s diet is another aspect of managing constipation. Providing high-quality, digestible forage and ensuring access to ample fresh water supports regular bowel movements and helps prevent the formation of dry, hard feces. ^[4]

After treating constipation, offering grass, haylage, or soft, moist foods like bran mashes is recommended to support gut motility. These foods add moisture and fiber to the diet, helping to keep the horse hydrated and promoting regular bowel movements.

Pain Management

Analgesics are often necessary to manage pain in horses with constipation, since abdominal discomfort can worsen the condition. Pain management typically involves non-steroidal anti-inflammatory drugs (NSAIDs). ^[4]

Effective pain relief helps the horse relax and improves overall comfort, which can help resolve constipation and promote normal digestive function.

However, certain painkillers, like detomidine hydrochloride, can slow gut motility and may worsen constipation if used frequently. Medications such as xylazine and flunixin meglumine are preferred, as they relieve pain without significantly affecting bowel function, making them safer options for managing constipation. ^[4][20]

Prevention

Maintaining a horse’s digestive health requires proactive management to reduce the risk of constipation or impaction. Key preventive measures include regular dental and veterinary care, along with ensuring adequate salt intake to promote proper hydration and digestion.

Hydration & Salt Intake

Maintaining proper hydration is vital for preventing constipation in horses. Horses should always have clean, fresh water available, and, in hot weather or after exercise, extra measures should be taken to encourage drinking.

Adding electrolyte supplements or flavorings to water can make it more appealing for some horses and boost intake. ^[21][22] Offering slightly warm water in colder weather or providing water-soaked feeds are also effective ways to increase hydration when a horse isn’t drinking enough on its own.

Salt intake is crucial for preventing dehydration and impaction colic. Salt is a source of sodium and chloride, two important electrolytes required in the equine diet.

Dehydration can cause water and electrolytes to shift from the hindgut to the bloodstream, leading to dry hindgut contents and increasing the risk of impaction. ^[23]

Feeding salt encourages thirst and increased water consumption, supporting gut motility, fluid balance, and overall digestive health.

Nutritionists recommend feeding horses 1 to 2 tablespoons of plain loose salt per day and providing free-choice salt in your horse’s environment. ^[24]

Dental & Veterinary Care

Regular dental check-ups are important for preventing constipation in horses because they ensure the horse can properly chew its food. When a horse has dental issues like sharp points, loose teeth, or uneven wear, it may not chew thoroughly, leading to larger, improperly digested feed particles entering the digestive tract.

Floating, or rasping, to smooth sharp teeth points and correct dental abnormalities is essential for dental health. ^[4][25] Proper chewing breaks feed into smaller, more digestible particles, improving digestion and lowering the risk of constipation and impaction. ^[26]

Routine veterinary check-ups are also critical for the early detection and management of health issues, including gastrointestinal disorders that can affect digestion. Veterinarians also provide guidance on diet, hydration, and practices that promote healthy digestion and prevent blockages.

Combined, proactive dental and veterinary care help maintain digestive health and prevent serious complications.

Prognosis

The prognosis for horses affected by constipation depends on the severity of the condition and how quickly it is treated. Early intervention with fluid therapy, dietary adjustments, and pain management usually leads to a smooth recovery without lasting complications.

However, severe or untreated cases can escalate into serious complications that may require surgical intervention. The outlook for impaction colic is generally good with prompt treatment, though severe cases may require surgery and ongoing management to prevent recurrence. ^[4]

Summary

Regular bowel movements are essential for a horse’s digestive health. Disruptions in gut motility can lead to constipation and colic.

• Signs of constipation include reduced fecal output, abdominal discomfort, and straining to defecate (Tenesmus)
• Constipation in horses may be caused by low-quality forage, ingestion of foreign objects, dehydration, or lack of movement.
• Effective veterinary treatment involves fluid therapy, laxatives, dietary changes, and pain management.
• Ensure proper hydration, salt intake, and regular dental and veterinary care to prevent constipation in your horse.