Impaction Colic in Horses: Signs, Diagnosis, Treatment & Prevention

Impaction colic in horses is a painful condition caused by an obstruction in the gastrointestinal (GI) tract. It is a serious and sometimes fatal condition. ^[1]

The term colic describes generalized abdominal pain or discomfort in horses. In many cases, this abdominal pain originates from the GI tract; but it’s important to remember that other organs in the abdomen can be a source of pain.

Cases of gastrointestinal colic are generally broken down into three types: spasmodic (gas), non-strangulating obstruction, and strangulating obstruction.

Impactions fall under the category of non-strangulating obstructions and refer to any type of blockage within the lumen of the GI tract. Often, it forms from dry feed (or digesta), but can also be caused by other foreign material, such as parasites, sand, and enteroliths. ^[2]

These blockages can prevent the normal passage of feed, gas and fluid through the digestive system, leading to mild or severe abdominal pain depending on the location of the impaction and its severity. ^[2]

Treatment for impaction colic includes giving analgesics for pain relief, rehydration and administering laxatives or psyllium to support intestinal motility. More complex cases may require surgery to remove the obstruction. ^[2][3][4][5]

The best way to prevent impaction colic is to offer ad libitum (free choice) access to good quality forage and fresh, clean water as well as keeping your horse’s diet and exercise schedule consistent. You should also avoid feeding your horse in sandy areas and follow a veterinarian-recommended deworming protocol.

If your horse is showing signs of colic, this is a medical emergency, and you should contact your veterinarian immediately.

Clinical Signs of Impaction Colic

Impaction colic symptoms are often easy to identify, but not all horses show the same signs. Symptoms vary greatly between individuals, based on the placement and severity of the blockage.

Sudden onset of the following signs behaviours can indicate abdominal pain and should not be ignored: ^[2][3][6]

• Reduced intestinal sounds
• Increased heart rate (over 64 bpm) or other changes in vital signs
• Reduced fecal output
• Pale gums
• Gastric reflux
• Sweating
• Abdominal distention
• Aversion to feed or loss of appetite
• Pacing, stretching and rolling
• Pawing at the ground
• Kicking or biting at the flanks or barrel

Affected horses often look depressed, uncomfortable or uneasy to their owners. They may seem uninterested in their surroundings and unable to focus.

Colic is always an emergency and should be considered whenever there is a deviation from normal behaviour in the horse. ^[6] If you suspect impaction colic, consult your veterinarian to obtain a diagnosis.

Is My Horse at Risk of Impaction Colic?

Any horse can colic, even with the best care, management and feeding. But some modern management practices, such as long-term stall confinement and intermittent feeding, are linked to a higher risk of colic.

Research shows that keeping a horse stalled most of the day without access to ad libitum forage can increase the risk of colic by over 50%. ^[4] Lack of movement and fasting between meals can also reduce gut motility and mucosal water transport and affect the microbiome, increasing colic risk. ^[1][2]

Sudden alterations to the horse’s routine and diet can upset the sensitive digestive system. If your horse is placed on stall rest due to illness or injury, the sudden reduction in mobility can affect digestion and the transit of feed through the gut.

Factors such as poor dentition, dehydration and rapid ingestion of feed may also put horses at higher risk of impaction colic. ^[7] Other suspected risk factors for colic include:

• High concentrate, low forage diets
• History of previous colic
• Administration of medication or dewormers in the previous month

Equine Digestive Tract Anatomy

Horses are hindgut fermenters, breaking down and extracting energy from forages using bacterial digestion. ^[1]

When the horse consumes feed, it first passes into the foregut – the stomach and small intestine – where the feed is broken down by enzymes.

The horse has a relatively small stomach compared to its body size. ^[7] Feed passes through the foregut quickly, allowing the horse to graze continuously throughout the day.

Feed then passes into the hindgut, which is the site of fibre fermentation. The hindgut includes the cecum, large colon, and small colon. Bacteria in the hindgut allow the horse to break down cellulose from forage and convert it into energy.

Interestingly, the horse is unable to vomit because the esophagus only allows feed and gas to move in one direction. This makes digestive upsets more severe for horses and can contribute to colic. ^[7]

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Common Sites of Impaction

The equine GI tract is full of twists and turns, and blockages can occur in any part of the system. However, some sites are more commonly affected than others.

Most impactions occur in the large colon, specifically at the pelvic flexure and transverse colon. At both of these locations, the diameter of the colon dramatically decreases in size, which increases the likelihood of digesta becoming stuck. ^[2][8]

The severity of colic symptoms and the horse’s physiological reaction depends on the location and size of the blockage. ^[2]

Partial obstructions occur in wider areas of the GI tract, such as the stomach, cecum and parts of the large colon. In this type of impaction, some fluid and gas can still pass around blockages or trapped digesta.

Total obstructions occur at sphincters or narrow parts of the intestine, such as the small intestine. In these cases, a part of the gastrointestinal tract is entirely blocked. Total obstructions can be fatal without intervention.

Pelvic Flexure Impaction

The most common area of feed impaction in the large colon is the pelvic flexure, which is the juncture between the left ventral colon and left dorsal colon. The pelvic flexure can be found in the lower left side of the abdomen. ^[2][8]

This part of the colon has a significant and sudden decrease in diameter and surface area, as well as a 180-degree hairpin turn. These features make it a common site for poor-quality hay or other dehydrated digesta to get stuck. ^[7][8]

Signs of pelvic flexure colic in the horse include mild or moderate intermittent pain and reduced fecal output. Risk factors associated with pelvic flexure impaction in horses include: ^[2]

• Poor quality forage
• Poor dentition
• Lack of water intake or dehydration
• Frequent and sudden management changes (stall rest, inconsistent exercise routine)

Pelvic flexure impactions can be common in areas with low-quality forage, and they usually respond well to prompt medical treatment.

Ileal Impaction

Ileal impaction occurs when the last 18 inches of the small intestine, or the ileum, becomes obstructed by digesta or a foreign body. The regular passage of feed, gas and fluids may be blocked, causing significant gut distension and colic symptoms. ^[2][8]

Cecal Impaction (Cecum)

The cecum is a large, blind-ended sac on the right side of the horse’s abdomen where the fermentation of feedstuffs occurs. It is 4-5 feet in length and contains bacteria capable of breaking down the cellulose in plants. ^[8]

The definite causes of cecal impaction are unknown but may involve feeding coarse roughage, sudden reduction in activity, some medications and parasites. ^[2][8]

Less Common Sites of Impaction

Gastric Impaction (Stomach)

Feed spends little time in the stomach (around 2-6 hours) compared to the entire transit time of digesta through the horse’s GI tract. However, the stomach can become overfilled if there is a foreign body or obstruction to the pylorus – the outflow tract from the stomach into the small intestine – that prevents normal clearance of feed material from the stomach.

Impaction in the stomach is rare and often goes undiagnosed until the horse happens to undergo gastroscopy, usually to diagnose gastric ulcers. Gastric impactions are generally resolved without surgery. ^[2][8]

Certain feedstuffs are associated with stomach impaction, including persimmon seeds, dehydrated beet pulp, pelleted feeds, straw, poor-quality hay and barley. These feeds can accumulate over time and cause the stomach to become large, distended, and at risk to rupture. ^[8][9]

Duodenal Impaction (Duodenum)

The duodenum is the first segment of the small intestine, positioned on the horse’s right side. The causes of duodenal impaction are unknown, and the condition is rare. ^[2][8]

Duodenal blockages form in close proximity to the pylorus, which is the exit from the stomach into the small intestine. This causes fluid from the duodenum to fill the stomach. The most prominent clinical sign of duodenal impaction is voluminous gastric reflux. ^[2]

The treatment for duodenal impaction is difficult, as obstructions in this part of the intestine tend to be inaccessible during exploratory abdominal surgery. If the obstruction cannot be successfully manipulated into a more accessible part of the small intestine for removal, then the prognosis for these cases is poor.

Jejunal Impaction (Jejunum)

The jejunum is the middle and longest section of the small intestine, reaching around 65 feet in length. Jejunal impaction is uncommon, and almost always develops in response to a primary illness or injury. ^[2][8]

Jejunal impaction is identified by gastric reflux, distention of the small intestine and pain in response to the distention. In most cases, the primary issue must be corrected surgically in order to resolve the impaction. ^[2]

Small Colon Impaction

The small colon is the final stretch of bowel between the large colon and rectum. Impaction of the small colon is infrequent, though may be seen in higher incidence in regions where enterolithiasis is common. ^[10]

Meconium retention is a specific cause of small colon impaction in newborn foals. This is when the foal fails to pass its first manure within a few hours after birth. Luckily the prognosis is excellent with prompt medical management. ^[8][10]

The prognosis for small impactions is considered excellent for cases successfully treated medically, and good for those requiring surgery. ^[10]

Causes of Impaction in the Digestive Tract

Blockages that contribute to impaction colic may be caused by parasites, poor-quality hay, sand ingestion, enterolith formation and ingestion of other foreign materials.

Parasites

Impaction in the small intestine specifically can be caused by a large burdens of Parascaris equorum, also known as ascarids or equine roundworms. Ascarids live in the small intestine. Ascarid infestation is usually observed in weanling foals or yearlings that have not been kept on consistent deworming programs. Affected foals may have a potbelly, slow growth and a poor-quality coat. ^[8][11]

Administering a highly-effective anthelmintic, such as ivermectin, to a horse with a large Ascarid population can paralyze thousands of parasites at once. This can lead to a sudden accumulation of dead worms in the intestine, obstructing the movement of feed, fluids and gas through the gastrointestinal tract. ^[8][11]

Research shows that horses with equine tapeworms (Anoplocephala perfoliata) are also a risk factor for ileal impaction. The tapeworms attach themselves to the junction between the ileum and cecum, where they can obstruct the bowel. ^[2][12][13]

Poor Quality Hay

Coastal Bermuda is a fine, stemmy hay that is a common forage source in the Southeastern United States. It is low in protein and energy and contains more fiber than cool-season grasses. ^[1]

Diets primarily consisting of Coastal Bermuda hay have been a risk factor for ileal impaction. However, hay quality is a bigger factor in impaction risk than forage species. ^[13]

Mature hay is considered lower in quality and less digestible. This makes it more likely to accumulate in the digestive tract, potentially causing an obstruction and colic.

Sand Ingestion

Sand impaction is usually seen in horses kept on sandy soil or paddocks. When the horse grazes or eats forages off of the ground, it may ingest sand and dirt which can accumulate in the gut, especially the large colon. ^[8][14]

Foreign Bodies & Enteroliths

In rare cases, horses may consume indigestible material that forms blockages in the digestive tract. Colic can occur if the foreign material gets stuck in narrow segments of the GI tract. ^[15]

Foreign bodies in the digestive tract can cause colic symptoms months or years after they are initially ingested. This type of impaction is more common in young horses, who tend to be curious and nibble on foreign objects. ^[15]

Materials that can cause impaction colic include but are not limited to fibers from lead ropes, twine, mesh, hair, rubber, pebbles and metal.

Impactions can also form due to enteroliths, which are accumulations of minerals that encompass indigestible objects in the bowel. Enteroliths form in the large colon over several years and resemble rocks or stones. If enteroliths move, they can block parts of the large or small colon, leading to colic. ^[8][16]

Higher levels of dietary magnesium, nitrogen and phosphorus paired with the alkaline environment of the colon contribute to enterolith formation. Enteroliths can be difficult to palpate and are usually removed surgically. ^[16]

Diagnosis & Examination

In order to diagnose impaction colic, your veterinarian will first look for indications of pain and take the horse’s vital signs. Some colicky horses display minimal clinical signs, so further examination is needed to make a diagnosis.

Auscultation & Gut Sounds

When digesta is moving normally through the GI tract, the horse’s gut tends to be noisy, producing gurgling, rumbling and bubbling noises. These sounds are caused by the movement of fluids and gas through the tract and are referred to as borborygmi. ^[7]

A sudden decrease or lack of gut sounds can be a sign of colic. Prior to colic diagnosis, the horse’s abdomen may be auscultated by your veterinarian to listen for evidence of hypomotility or decreased movement.

In cases of sand impaction, the gut sounds from under the belly often sound gritty and resemble crashing waves. The noises vary in intensity and duration, depending on the amount of sand accumulated. ^[14]

Rectal Examination

A rectal exam is an important diagnostic tool when dealing with a potential impaction. This process involves your veterinarian palpating the inside of the abdomen through the rectal wall to feel for any blockages or abnormalities in the abdomen. ^[3][4][5]

Several organs can be palpated during a rectal examination to identify impactions, including the pelvic flexure, small colon, cecal base and ventral cecal band. The small intestine is not palpable in a healthy horse. ^[8]

If your veterinarian identifies an abnormality on rectal exam, they will decide the best course of treatment for your horse. Rectal exams should be performed on any horse with abdominal pain, sudden weight loss or aversion to feed.

Unfortunately, horses can have normal rectal examination findings when the impactions are located further up the GI tract, out of the reach of the veterinarian’s arm. The equine abdomen is large and many areas cannot be thoroughly assessed via rectal palpation, so other diagnostic methods are required for these areas.

Nasogastric Intubation

Nasogastric intubation is a procedure that enables your veterinarian to directly access the horse’s stomach and relieve pressure. The veterinarian inserts a tube through the horse’s nostrils until it reaches the stomach.

This procedure is used to assess stomach contents and identify blockages or gas and fluid build-up. Veterinarians also use nasogastric intubation to administer fluid and medications directly into the horse’s digestive tract or to remove some obstructions. ^[3][4]

Ultrasound Imagery

Diagnostic abdominal ultrasounds can be used to detect extra fluid in the abdomen, a distended small intestine and foreign bodies in the GI tract. ^[3][5]

Sand accumulation in the large colon is commonly diagnosed using ultrasonography or radiography. ^[8]

Treatment

Pain Management

Acute colic is associated with significant pain in horses, which can cause your horse to become anxious and hurt themselves or the people around them. Once vital signs have been taken, pain relief should be administered immediately by a veterinarian. ^[3][4][5]

Common pain medications for impaction colic include nonsteroidal anti-inflammatory drugs (NSAIDs) such as flunixin meglumine (Banamine). Administering Banamine at an appropriate dosage specified by a veterinarian can help maintain intestinal motility and reduce pain in horses with impaction colic.

Xylazine and detomidine are fast-acting, effective sedatives that may be administered by a clinician to reduce pain and sedate the horse. They provide temporary pain relief by relaxing the intestine surrounding the impaction. This allows some gas and fluid to move around any blockages.

Other medications, such as opioids or spasmolytics, may be used to control symptoms.

Hydration

Enteral (Oral) Fluids

The passage of feed through the long and winding digestive tract requires a lot of fluid to ease transport. Dehydration impairs the horse’s ability to pass feed through its digestive system.

Impactions can sometimes be broken up and moved through the gut with the help of water lavages to promote hydration and lubrication. ^[3] Lavages are typically administered through a nasogastric tube.

Multiple water lavages may be warranted if a veterinarian believes a horse has an obstruction. However, horses must be carefully monitored during treatment, as large-volume lavage can cause abdominal pain or distension. ^[3][5]

Intravenous (IV) Fluids

Most horses with impaction colic are dehydrated to some degree. Horses with gut obstruction can have trouble absorbing water normally through the small intestines.

A balanced electrolyte solution may be administered to help rehydrate horses. Fluids are administered intravenously or directly into a vein to bypass the gastrointestinal tract. ^[3]

This helps to promote the hydration, breakdown and transit of trapped digesta. Between 40 to 80 litres of IV fluids may be administered throughout the day to help loosen impactions.

A knowledgeable clinician and staff must carefully monitor the horse while administering fluid to avoid overhydration. The amount of fluid being administered and catheter placement should also be carefully considered. ^[3]

Laxatives

Magnesium sulfate (Epsom salt) is used to treat impactions in the cecum, large colon and small colon. It works by helping to rehydrate the dry, firm feed material forming the impaction. It is administered via nasogastric tube dissolved in a large bucket of water. ^[3][5]

Traditionally, mineral oil was administered enterally (via nasogastric tube) to treat impactions. The thought was that the oil helped lubricate the gut to allow the impaction to pass more easily. However, magnesium sulfate has been shown to be superior in treating impactions. ^[3]

Psyllium mucilloid may be administered to help remove sand accumulations in the large colon of the horse. Psyllium fiber forms a gel when mixed with water and is thought to stimulate gut motility and peristalsis, pushing ingesta and sand through the digestive tract. ^[8]

Surgery

A horse suspected of having a total gut obstruction or with signs of severe abdominal pain is a candidate for emergency colic surgery.

Some horses with total GI tract impactions remain in stable condition with mild pain for extended periods, so they are not always immediately referred for surgery. ^[8] Consult with your veterinarian to determine the appropriate treatment for your horse.

Prevention

There are several management practices that you can implement to help reduce your horse’s risk of developing impaction colic and support gut motility. The most important factors to prevent gut blockages include providing constant access to water and encouraging hydration, feeding quality forage and giving your horse adequate turnout or exercise. ^[4]

Water & Feed

Horses should have access to fresh, clean water at all times. ^[1][4] Feed salt and electrolytes to encourage hydration, especially in hot weather or after working your horse. Soaking feeds can also promote hydration.

Horses should also have free-choice access to appropriate quality forage to mimic their natural feeding behaviour. Check hay for excess debris and choose higher-quality hay that is easier for the horse to digest.

If you only have access to low-quality forage, consider soaking or steaming coarse hay to improve digestibility. Horses with dental issues may not be able to break long-stem fibers into smaller pieces, so consider hay cubes or chopped hay as alternatives.

All feeding systems, such as tubs or buckets, should be slightly raised off the ground to prevent accidental sand ingestion. Prevent your horse from grazing on short grass and scrounging in the dirt to limit sand accumulation in the gut.

Management

Daily turnout and exercise promote intestinal motility, defined as the passage of food through the intestines. Horses are grazing animals that evolved to roam vast distances, and they need plenty of opportunities to express freedom of movement.

Adequate deworming programs should be implemented for all horses, especially young horses at high risk of ascarid or tapeworm infestation. ^[4][11][12]

Prognosis

Colic is serious and should always be treated as a veterinary emergency. Prompt intervention at the first signs of impaction colic is critical for a good outcome.

To determine the prognosis of a horse with impaction colic, the size of the blockage and its location must be considered. However, every case is different and some horses respond to treatment better than others.

If the obstruction can be treated medically with non-invasive techniques, the prognosis is generally excellent. However, the site and severity of the impaction will dictate whether or not medical management is successful. Prognosis associated with surgery depends on the case. ^[3]

Summary

• Impaction colic involves abdominal pain or discomfort in a horse’s gastrointestinal tract. Incidences of impaction colic may be identified through various clinical signs.
• All horses are susceptible to colic, but the risk is higher in horses that do not receive ad libitum forage or water and horses that lack proper exercise or turnout.
• Horses are hindgut fermenters with the inability to regurgitate feedstuffs. The anatomy and size of the horse’s gastrointestinal tract lead to several different sites of impaction.
• Impaction may be initiated by causes including parasite load, poor-quality hay, sand ingestion and/or foreign bodies and enteroliths.
• Impaction may be treated with various interventions, depending on the location and severity of the occurrence.
• Preventative management practices can help to decrease the risk of impaction colic, including encouraging hydration and choosing the right forage.
• Immediate response to signs of impaction colic will improve the prognosis and outcome for affected horses.