By James Bryant, DVM, Diplomate ACVS

Colic is a word that no horse owner wants to hear, particularly as it pertains to their beloved equine athlete during or just after completing an endurance ride. Endurance horses are at an increased risk for colic episodes due to management changes and the strenuous exercise associated with the event.

An understanding of colic and the risk factors associated with endurance horses can help the rider to decrease these risks. The rider is the most important person in decreasing the risks associated with colic. The rider is also the person who can identify the warning signs or first clinical signs so that proper care and treatment can ensue.

No one wants to experience the need for treatment of their horse for colic at a ride or the possible loss of their horse related to colic. This article is the first of a two-part series discussing the causes, clinical signs, treatment and prevention of colic in horses and specifically how it relates to the endurance horse.

What is colic?

Colic is the general term for abdominal pain in the horse, regardless of cause. In the general horse population colic is a serious cause of morbidity (illness) and mortality (death). Over the past several years equine fatalities at or after rides have been reported that are the direct result of a colic episode.

In recent studies the risk of a colic event was 4.2 colic events per 100 horses. Of these colic events the fatality rate was 11% of the affected horses and 1.4% of the colic events required abdominal surgery.

Other research studies have found certain factors that are associated with an increased risk of colic. Among these are several that pertain directly to endurance horses. These include:

— a recent history of travel

— recent changes in the feeding schedule or type of feed

— changes in water intake

— recent history of a change in exercise level (i.e., a strenuous exercise event).

These factors are obviously important to our endurance horses because often these horses travel several hours or days to a ride, have a change in their feeding schedule and have a disrupted water intake schedule due to the time in the trailer. Add to this the strenuous exercise and we are looking at a situation that carries with it an increased risk for colic.

As we look at colic and go through the second part of this article on prevention, we will see how important you, as the owner, are to controlling these risk factors and allowing your athletic horse to perform well and free from the negative effects of illness and treatment.

Abdominal pain (colic) is caused by either distention of the intestine with gas, feed or liquid or a pull on the blood supply (mesentery of the intestine) by the distended or twisted intestine. Twisted intestine is associated with the most acute pain and often quickly results in compromise or death to the affected portion of intestine. These types of colic are the most serious and painful.

There are many types and causes of abdominal pain and not just those associated with the rigors of an endurance event. It is important to remember this as some causes of colic occur in endurance horses at an event that have no bearing on the fact that these horse have competed in an endurance event. Included in this group are enteroliths (stones formed in the intestine), bowel that has been strangulated (twisted) with a lipoma (fat growth), or types of tumors (cancers) that involve the intestinal tract of horses. These types of colic would have occurred at any time and happened to be associated with the timing of the endurance event.

Types of colic seen at rides

Looking specifically at an endurance horse at an event, there are certain types of colic that are associated with the event and require recognition by the owner and veterinarians at the ride. These include:

— impactions of feed

— ileus (lack of intestinal motility)

— gas colics (excessive gas build-up)

— stomach-related issues.

Colic symptoms can occur at any time during the event including prior to or leading up to the ride, during and after the ride as well as after returning home. However, frequently abdominal pain (colic) will manifest during or immediately after the ride.

Ileus is probably the most important cause of colic in endurance horses. Ileus is the lack of progressive motility in the intestine. This can affect the small intestine, the large intestine and small colon. One or more of these may be affected at any time. Another term we should be familiar with is segmental ileus; this occurs when, within a given section of bowel, part of the bowel is motile and part is undergoing ileus. Segmental ileus is important because it is a cause of strangulation in the small intestine. In endurance horses that require abdominal surgery small intestinal volvulus (twist) can be diagnosed and is usually a result of segmental ileus.

The cause or triggers for ileus are multifactorial in endurance horses. Normal intestinal motility is maintained by electrolytes, specifically calcium, sodium and potassium, and normal blood flow (volume). In the endurance horse the loss of electrolytes through sweating and electrolyte shifts between the intracellular and extracellular spaces with exercise are well documented. If the losses of electrolytes are greater than the body’s ability to keep up or replace them, decreased motility in the intestinal tract may occur.

The body also physiologically slows down the intestinal tract as it moves blood supply to the heart, lungs and brain to meet the demands of exercise. This physiologic response is normal and could be expected during the first part of the ride (this may be why your horse has lower gut sounds at the first vet check). However, if your horse always has good gut sounds at the first check and at a particular ride has decreased gut sounds this may be a sign to watch closely as the day progresses.

Ileus can cause colic in a number of ways, either through gas build-up, feed impactions, mechanical obstructions or potentially through twists of the small intestine. When the intestinal tract slows down then feed material may become impacted (dehydrated), or the segments without motility may fill with fluid or gas from the sections that are functioning normally and become distended, or if the front part of the small intestine stops then the stomach may fill with fluid or feed because it is not emptying properly.

Horses cannot vomit; therefore when their stomach is expanded beyond a normal amount, they may exhibit colic signs. This is the single most important reason to pass a nasogastric tube in the colicking endurance horse. The stomach will rupture before a horse vomits (they can’t) and these are fatal events. Ileus, therefore, may be a cause of colic by itself or lead to other types including impactions, obstructions and inflamed intestine.

Other types of colics associated with endurance events include impactions of the large intestine which could be due to any combination of the following:

— decreased water intake before, during or after the ride

— decreased motility

— a change in hay.

The change of hay is particularly important in the Southeastern states where coastal bermuda grass hay is fed. This leads to a certain type of impaction called an ileal impaction. Ileal impactions are more likely to occur in horses that are receiving coastal bermuda hay for the first time.

Endurance horses are at risk for large colon impactions at any time because of the physical changes in water intake, ileus (lack of intestinal motility), and the dehydration associated with exercise during the ride. Impactions may not appear clinically until the horse has left the ride site or is at home for one or two days. If your horse has shown any signs of colic it is important to monitor the amount of manure produced, especially if an impaction is suspected.

Impactions of the stomach do occur in endurance horses related in particular to lack of intestinal motility, decreased water intake and continued eating until the stomach is distended and painful. These impactions, if not treated appropriately, can lead to stomach rupture. Stomach impactions can be difficult to diagnose and often go unrecognized. The presence of feed material in the stomach after repeated nasogastric intubations, with persistent low grade pain and ileus, may allow the veterinarian to assume a stomach impaction is present and institute appropriate therapy.

Symptoms of colic

The clinical signs of colic are varied and because of this may be missed at first, when only mild signs are present. Clinical signs can include loss of appetite, depression, flank watching, pawing, lying down, rolling, and more violent behavior. In the endurance horse often the loss of appetite is the first clinical sign seen. We have often associated appetite as sign that endurance horses are performing well and are having a good ride. This is an important sign and the more rides you do with a particular horse it is important to pay attention to their eating habits throughout the ride.

Clinical signs of colic during the ride range from decreased or lack of appetite, to intermittent or constant pawing to the more severe sign of trying to go down or rolling. During a ride these signs should never be overlooked and immediate action should be instituted. Unfortunately when we look back at cases of colic that have resulted in referral to clinic situations or fatalities we can correlate subtle changes in the horse’s behavior earlier in the ride with the eventual clinical signs of colic. This underscores the point of the rider knowing their horse well and recognizing any changes from their normal ride behavior.

Diagnosing colic

The diagnosis of colic and determination of a particular type begins with the recognition of the clinical signs of the horse. Then through accumulation of the data, associated with the history, physical examination findings, rectal exam findings, nasogastric intubation and blood work, the veterinarian arrives at a tentative or working diagnosis. Initial treatment may then be continued (i.e., the use of pain medications) or further treatments will be instituted including IV fluids.

During the diagnostic part of the exam, veterinarians use the presence or absence of reflux (fluid or feed back from the stomach) in determining if the stomach can empty. The presence of reflux (fluid accumulation) indicates the potential for an obstruction of feed or fluid in the small intestine. Ileus is a form of mechanical obstruction whereby the intestine cannot empty because of a lack of progressive (forward) motility. In addition, the lack of gut sounds (a crude estimate of intestinal motility) indicates that the intestinal tract may not be functioning properly.

From the obtained information the treatment plan is determined and recommended. This may include anti-inflammatories, fluid therapy, administration of oral fluids and careful monitoring for a recurrence of the abdominal pain. If the pain is severe or persists then referral to a surgical facility is generally recommended.

Surgical types of colics include twists of the intestine, impactions that do not respond to medical therapy, prolonged ileus or enteritis. Enteritis is persistent inflammation of the small intestine and may result from prolonged ileus or distention of the bowel. Factors that veterinarians and veterinary surgeons use to determine if there is a surgical lesion are degree of pain, response to pain medications, presence of abnormalities on rectal exam, presence or persistence of reflux from the stomach and, most importantly, persistent pain that does not respond to therapy.

Fortunately most of the colics at endurance events will respond to medical therapy and will not require surgical intervention. If surgical intervention is needed, a thorough discussion of the prognosis, complications and costs should occur with the veterinarians involved.

Recognition of colic signs is vital to early and appropriate therapy to prevent the need for referral or surgical intervention. The rider is ultimately the most important person in determining that the horse is having a good day and no warning signs of colic are seen.

In Part 2 the topics of treatment and prevention of colic will be discussed.