Colic. In the world of horses, there are few words that can cause as much concern as this.

For owners, riders, and veterinarians alike, colic has a major impact on the equine industry. A 2005 scientific paper reported that colic is responsible for more deaths in horses that any disease group except for old age. In the equine population, horse mortality from all types of colic was 0.7 deaths per 100 horse-years with 6.7% of colics being fatal. Though there is no study examining the number of abdominal surgeries performed for colic alone, an estimate based on the smaller studies, anecdotal numbers of surgeries at clinics, and the total number of horses in the United States is approximately 12-24 thousand colic surgeries performed per year or possibly as many as 2.7 colic surgeries every hour. An estimate of the total cost of colic to the equine industry is $144,000,000.00 per year. Besides the economic impact of colic, there are the emotional and physical stresses to both the horse and owner that need to be considered. .   Equine colic is very simply a condition of abdominal pain. That is all that is simple about colic. The symptoms of colic are most often telltale. A horse with colic may be partially or completely off his feed, have decreased or absent manure production, be seen to look back at the abdomen, stretch out or posture to urinate, lie down, paw, flip the upper lip, or progress to violent thrashing on the ground. Although the symptoms of colic are somewhat universal, the causes of colic are numerous.   To better understand colic, a review of the anatomy of the gastrointestinal tract (GI tract) will be helpful. The equine GI tract originates at the mouth. Feed passes from the mouth down the esophagus to the stomach. From the stomach, ingesta passes into the small intestines, to the cecum, large colon, transverse colon, small colon, to the rectum and exits as manure via the anus.

Equine GI tract anatomy

Here are some important details about the equine GI tract:

  • The muscular contractions along the esophagus will only allow food to move normograde from the mouth to the stomach and not retrograde
  • The stomach has two different linings. The lining of the upper portion of the stomach is called the “non glandular” or squamous mucosa and the lining of the lower portion of the stomach is called the “glandular” mucosa. It is in the glandular mucosa that acid, mucus, and digestive enzymes are secreted.
  • The small intestines are connected to the body by a structure called the mesentery which is a ligamentous attachment anchored near the first and second lumbar vertebrae of the spine. This area of attachment is called the root of the mesentery. The mesentery runs the entire length of the small intestines and is what allows the small intestines to be more freely moveable than the remainder of the GI tract
  • The equine cecum is very large, up to 1.25 meters in length, with a capacity of over 20 liters. The cecum is part of the large intestines and is known as the “fermentation vat” of the GI tract. Both the cecum and the large colon house enteric bacteria that are required for normal digestion and nutrient absorption.
  • The large colon exists in various diameters changing from 5 cm at the junction with the cecum, to 25 cm on the floor of the abdomen, to 8 cm at the pelvic flexure, to 50 cm before arriving at the transverse colon.

The anatomical structure of the equine GI tract unfortunately lends itself to colic if conditions are not ideal. So now on to our colicking horse.   A horse that is evaluated by the veterinarian for colic has a number of standard procedures performed in an attempt to further identify the specific cause of colic. A complete physical exam is performed to include assessment of the heart rate, respiratory rate, temperature, mucous membrane quality, color, and moisture, and the activity level of the gastrointestinal tract. The heart rate is the most sensitive indicator of pain and can give the veterinarian an idea of how serious the colic is. The presence, absence, overabundance, and quality of the gastrointestinal sounds can give a clue as to the underlying cause of the colic.

Physical Exam

Following the physical exam, most often times a rectal exam is performed. During the rectal exam, the veterinarian advances their hand thru the anus and reaches up to their upper arm into the rectum of the horse. Once positioned, the veterinarian can palpate the caudal (back) approximately 1/3 of the abdomen. The structures typically palpated during the rectal exam include the spleen, the caudal pole of the left kidney, the caudal aorta, the cecum, the bladder, the ovaries and uterus in a mare, and the caudal aspect of the large colon including the pelvic flexure. Abnormal structures that can be encountered on rectal exam include small intestines that have been forced further back than they belong and tumors or masses. During the rectal exam, the veterinarian continues to gather information regarding the underlying cause of the colic. Possible abnormal findings on the rectal exam include

  • the presence of normal or distended small intestines indicating proximal enteritis (inflammation of the small intestines resulting in hyper secretion of fluid and decreased or absent motility), a strangulating lesion of the small intestines, or a torsion of the small intestines at the root of the mesentery
  • excessive accumulation of overly firm and dry ingesta in the large colon indicating a large colon impaction
  • accumulation of excessive fecal balls in the small colon indicating a small colon impaction
  • overly fluidy content of the small or large colon suggesting diarrhea as a cause of colic
  • gas distension of the large colon indicating a gas colic
  • the presence of large colon between the spleen and the left kidney indicating a nephrosplenic entrapment
  • abnormal positioning of the large colon indicating either a large colon displacement or a large colon torsion (aka “twisted gut”)

It is also possible for the rectal exam to be completely normal in a horse that is presenting for colic.   Following the rectal exam, a nasogastric tube is passed. This involves advancing a soft siliconized plastic tube up the nasal passage, thru the pharynx, along the esophagus, and into the stomach of the horse. Passing of the stomach tube provides additional information to the veterinarian. Possible abnormal findings include the presence of foul smelling gas in the stomach or the accumulation of excessive fluid or feed material in the stomach. Passing of the stomach tube allows for evaluation of the cranial (front) approximate ¼ of the gastrointestinal tract. The remaining portion of the gastrointestinal tract between that which is evaluated by rectal exam and that which is evaluated via passing of the nasogastric tube can be evaluated with transabdominal ultrasound.

Nasogastric intubation

Following the physical exam, rectal exam, passing of the nasogastric tube and possible abdominal ultrasound, the veterinarian will have most often identified the underlying cause of the colic and initiate the appropriate treatment. Here are the most common causes of colics and how they are treated.

  • Gas colic – This type of colic is the result of excessive production of gas within the GI tract or inability to pass a normal amount of gas out of the GI tract. The most common sites of gas distension are the large colon and cecum but it can also occur in the small intestine. Gas distention of GI tract triggers pain sensitive receptors in the intestinal wall and initiates the clinical symptoms of colic.

Gas colics are most often times treated medically with the IV administration of sedation, analgesic medication (Banamine), and anti-spasmodic medication. Additionally mineral oil and warm water are often administered via the nasogastric tube. This encourages peristalsis (involuntary wavelike contractions of the muscular wall of the intestines that advances contents onward) and helps to maintain hydration. Occasionally a gas colic will fail to respond to medical treatment and require surgical intervention at which time the gas distended portion of the GI tract is decompressed or a gas distended abnormally positioned structure is decompressed and returned to its proper location.   There is evidence that suggests a link between changes in a horse’s feed regimen and the onset of a gas colic episode. A horse’s diet should always include constant access to good quality forage and clean water and changes in the diet be made gradually. Paying attention to good nutritional management should help reduce the likelihood of a gas colic.

  • Impaction colic – Impaction colics are the result of excessive accumulation of ingesta or fecal material within the GI tract. They can occur in the small colon, large colon, and even the cecum. By far the most common site of impaction is the large colon. As previously discussed, the large colon has areas of multiple diameters and it is at the areas of narrowing that impactions typically occur, i.e. the pelvic flexure. The two biggest factors influencing the development of an impaction colic are the hydration status of the ingesta and the motility of the GI tract. Motility is the movement of the digestive system and transit of its contents. It is the normal job of the cecum and colon to resorb fluid content of ingesta back into circulation. Normally 30 – 40 gallons of fluid are secreted daily during the process of digestion, of which 90% is resorbed before manure is formed. Motility is best stimulated by the volume of food and water introduced to the GI tract. Delayed passage of ingesta thru the colon allows for additional water to be absorbed and the end result is drier fecal content that is more prone to become impacted.

Impaction colics are most often treated medically with the IV administration of sedation and analgesic medication (Banamine), softening the consistency of the impacted ingesta with administration of fluids and softening agents either via nasogastric tube and/or IV, and re-establishing GI motility to improve fecal transit. Methods to improve motility include hand walking and even trailering. The majority of impaction colics are successfully treated medically but a small percentage can progress to needing surgical intervention. Rapid identification and aggressive treatment are keys to a successful outcome.   From a management standpoint, certain things can be done to decrease the likelihood of an impaction colic. Maximum turnout is very beneficial. In fact, a study has shown that 53% of impaction colics are associated with recent stall confinement and that 62% of impaction colics occurred within 2 weeks of significant management changes such as strict stall confinement or travel. In addition to turnout, regular exercise is beneficial in that it improves metabolism and GI motility. Also, unlimited access to high quality forage and fresh water are beneficial. High fiber diets, as compared to diets with significant grain products, increase colonic water content by at least 30%. Lastly, dental maintenance to allow for optimum mastication of feed stuffs improves digestion and overall GI function.

  • GI ulcers – Colic associated with GI ulcers can either be mild and chronic or acute and severe. Gastric ulcers in horses are quite common and their prevalence has been estimated from 50% – 90% depending on discipline and management of the horse. Gastric ulcerations are the result of excessive acidic pH in the upper portion of the stomach covered by the non glandular or squamous mucosa. This portion of the stomach has minimal protection from stomach acid. In contrast, the lower portion of the stomach covered by the glandular mucosa produces the acid but also produces mucus and bicarbonate to protect it. Horses are designed to consume small amounts of feed over extended periods of time therefore their stomachs produce acid 24 hours a day. Up to 9 gallons of acidic fluid can be produced by the stomach daily. In normal grazing scenarios, this acid is buffered by the presence of the high roughage feed stuff and saliva. In common performance horse and companion horse management programs, horses are fed 2 large grain meals daily and have periods without access to forage leaving the stomach susceptible to ulcer formation.

A horse that is colicking as a result of GI ulcers may very well have had other subtle signs leading up to this event. Other symptoms of GI ulcers include poor appetite, weight loss, poor body condition or muscling, change in personality or dullness, change in performance, reluctance to train, poor hair coat, increased sensitivity to grooming or girthing, dunking feed in the water bucket, increased periods of lying down, mild colics, and loose manure.   Acute GI ulcer origin colics are typically treated with the IV administration of sedation and analgesic medication (Banamine). Although Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) such as Banamine are known to initiate and perpetuate gastric ulcers, a single dose in a crisis event tends to be helpful. Most importantly, initiating treatment with Omeprazole (Gastrogard) and instituting management changes are a necessity in the successful treatment and resolution of gastric ulcers. It should be noted that to definitively diagnose active GI ulcers, a gastroscopy must be performed. It is NOT standard protocol to perform a gastroscopy in a field setting. Often times a horse being evaluated by the veterinarian for colic will be treated on the suspicion of GI ulcers as being the cause and once stabilized the horse is referred to a hospital setting for gastroscopy and definitive diagnosis. In a large veterinary school study, 50% of the horses that presented for colic had gastric ulcers. The ultimate question is whether the colic was the result of the ulcers or the ulcers were the result of the colic!   Horses with gastric ulcers benefit from maximum turnout and constant access to high quality pasture or forage, a decrease the size of grain meals, avoiding textured feed, feeding a small amount of alfalfa hay daily, minimizing stressful situations such as trailering or introduction of new pasture or stall mates and avoiding or reducing the amount of NSAID medication used.   In addition to gas colics, impaction colics, and GI ulcer origin colics, there are certainly other causes of colic and although it is always the veterinarian’s goal to pinpoint the exact cause of a colic episode, there are instances where this isn’t possible. I often times say each horse is entitled to a foot abscess, a fever, and an episode of colic in its life. It seems to be part of being a horse. However, on the day of the colic episode please take your horses condition seriously. What appears to be a mild problem can progress to a life threatening emergency without proper treatment.