By Jay Mero, DVM

Originally published in the October 2016 Endurance News

Few situations strike fear in the heart of a horse owner as colic does. Colic is one of those things that it’s not if it happens to you and your horse, but rather — if you own horses long enough — it’s when and how bad.

Luckily, in the general equine population, colic — defined as abdominal or gastrointestinal pain — is usually something simple such as gas bubbles, cramps or other minor, non-life-threatening causes. Colic can range from mild cramping, pawing the ground and a refusal to eat, all the way to severe abdominal pain with horses thrashing and rolling violently, up and down on the ground, as severe colics will often do.


Causes of colic

In the general equine population, research has worked out several reasons that are directly related or known to cause colic issues, the most common reason being a sudden, abrupt change in hay. Other common reasons known to promote colic in horses:
— feeding or consuming too much grain
— not drinking enough water in extreme temperatures
— ingesting sand or other debris when fed off the ground
— enterolith or stone development from diets rich in alfalfa in the West and Southwest
— cancer in aged animals
— and, basically, any other change to a horse’s routine or management such as transportation, changes in housing, over-exercise, and other feed changes, particularly in sensitive animals.

In the sport of endurance, over the past 50-plus years, veterinarians and researchers have developed a greater knowledge and understanding of the metabolically sick endurance horse. While there are several common metabolic problems that occur in the sport of endurance such as exertional rhabdomyolsis, exhausted horse syndrome and hyperthermia to name a few, colic is the number one reason horses become sick at endurance events and accounts for 80% of the fatalities in AERC endurance.

Secondly, many experienced veterinarians involved with the sport of endurance now recognize treating the sick endurance horse has evolved into a sub-speciality of treatment. In fact, the average colic case at an endurance ride is often so unlike what is seen in routine practice, it is very important treatment vets working rides are familiar with the differences and specifics of treating the endurance horse colic.

Additionally, we have now come to appreciate colic in the endurance horse can occur at any time — before, during or after an endurance ride. Colic is not a phenomenon which only strikes the fastest competing horses, nor does it only affect 100-mile horses. While speed and distance do increase the risk of a colic event, colic occurs in limited distance events, with mid-pack riders, and even last place finishers of all distances. Colic can even strike minutes to hours after the ride, when everything seems well, even after a day full of all A’s on that vet card.

The leading causes of colic in the endurance horse are dehydration, poor gastrointestinal blood flow and electrolyte disturbances. However any upsets in routine such as changes in feed, trailering stress, too much or too little electrolytes, over-exertion and even ulcers can all contribute to colic in the endurance horse. While displacements and twists of the gastrointestinal tract can occur, more typically reduced overall gut motility, resulting in an ileus caused by the cascade of dehydration, hypovolemia (blood shunting away to the working muscles) and electrolyte imbalances all leads to colic and abdominal pain.

Pain arises from gas production in a stagnant bowel and from the stretching of the intestines by the accumulating gut fluids. Impactions of the large bowel or colon can also occur simply from dehydration causing feces to become hard, dry and stuck.


Signs and symptoms

Colic in the endurance horse can present with a spectrum of signs and symptoms. Sometimes the signs are vague and subtle, and sometimes it probably feels to riders like the sky has fallen when their horse suddenly becomes violently painful and is flopping around on the ground like a fish out of water.

Colic often starts long before the outward signs of pain are evident. A change in attitude, loss of eagerness to go, reluctance to eat or drink, rising heart rates on trail, and sluggish heart rate recoveries in holds and/or poor to absent gut sounds at vet checks are all potential red flags and warning signs that trouble could be imminent.

Riders super-attuned to these subtle changes may be able to adjust their riding strategies and management style and make changes fast enough to overt disaster. Slowing down, cooling the horse, adjusting electrolytes and taking extra time in the holds to allow the horse to eat and drink more are all excellent strategies that sometimes make all the difference needed between having a happily-ending day and a horse ending up on an IV.

To be fair, in some cases, there are no subtle signals and colic “just happens.” But in many cases, particularly as we have gotten better at reviewing treatment and fatality scenarios, there was some kind of early warning that was missed and potentially might have been that moment where a crisis could have been averted if it was caught early enough.

Riders should work hard to “listen” to their horses and know the feel of their horse when everything is “right,” as opposed to when something just feels “off.”

Do NOT ignore that inner feeling or voice you the rider might have that something is just not right. Do NOT rely on the veterinarians working the ride to “catch” your horse and notice those subtle signals, as they only get a short, few minute-glimpse of your horse, a quick snapshot in time, as opposed to you being with your horse all day long.

As the sick endurance horse progresses towards more serious disease, and potentially a life-threatening colic and ileus scenario, some of the not-so-subtle symptoms are:
— a failure to recover the heart rate within 20 to 30 minutes
— an inverted CRI
— poor to absent gut sounds, particularly in a horse that is refusing to eat or drink
— dull expressions
— signs of dehydration such as dry mucous membranes and poor jugular refill
— lethargy
— not wanting to trot out
— potentially mild, moderate and even severe abdominal pain.

Interestingly, we have also come to recognize that colic can exist with other metabolic problems as well. For example, the tying-up horse, or an exhausted, overheated horse are at risk for developing colic along with their other problems. It is not uncommon to have a horse on IVs being treated for a different primary problem suddenly develop colic pain as treatment progresses.


Don’t wait to treat

While it is obvious the horse flopping on the ground in pain needs treatment, do not be fooled by the horse that is just not doing quite right. Oftentimes owners wait and wait, hoping eventually their horse will show an interest in eating and will perk up after a little rest. Sometimes this strategy works, but more often than not the owner is just prolonging eventual treatment and potentially raising the risk of a much more serious event happening.

Treatment of the colicking endurance horse starts with a thorough examination by the treatment veterinarian. Assessment of the pain level, hydration status, temperature, heart rate, gut sounds and overall demeanor are all major parameters evaluated.

In many cases on-site blood tests assessing electrolytes, hydration levels, muscle function, etc., are becoming more common. Passage of a nasogastric tube is used to assess the presence of ileus and is often left in place, taped to a halter, to facilitate frequent reassessment of gut motility as needed.

The cornerstone of all treatment for the sick, metabolic and/or colicking endurance horse is rapid, large-volume intravenous fluid replacement therapy.

As fluid therapy is initiated the treatment veterinarian will often use pain medications to facilitate both the exam and treatment of the colicking horse to control abdominal pain and discomfort. If nonsteroidal medications such as flunixin (Banamine) are used, then very low, judicious doses are applied as NSAIDs can be fatal in a severely dehydrated horse. Rectal palpations to determine potential displacements, twists or impactions are also carefully considered and used cautiously in the dehydrated horse.

Additional medications in the intravenous fluids are often added to correct electrolyte imbalances. And careful oral fluid therapy can be applied if the gastrointestinal tract is functional and motile.


Endurance colics are different

A major difference between endurance colics and routine private practice colics is the shocking intensity of the pain in the endurance horse with a fairly low heart rate, usually related to the ileus syndrome and not a surgical lesion at all.

In veterinary school we are all taught severe, intractable pain usually corresponds with high heart rates and surgical lesions such as twists or displacements. Due to the gut stasis in the endurance horse colic, our horses can be in dramatic pain, requiring repeated doses of pain medications to control the discomfort, yet they are not suffering from a problem requiring surgery at all, rather they just need time and patient treatment as their gastrointestinal (GI) system struggles to become functional again.

Secondly, we are also taught in vet school that most colics require large volumes of IV fluid replacement (50 liters on up) to make much of a difference in treatment. However, as field treatment of endurance horses has improved, we have now come to appreciate that many horses, in fact the majority of horses, will improve and recover rapidly and uneventfully with as little as 10 to 20 liters of intravenous fluid therapy.

This contrast in severe, recurrent pain, most commonly caused by ileus in the sick endurance horse — as compared to the standard gas, spasmodic colic that improves with just a dose of sedation and Banamine in the rest of the equine world — can potentially lead to an endurance horse being euthanized too quickly and not given enough time on medications and IV fluids to recover.


Becoming more progressive

This is where we as a collective group — riders, owners, ride managers, veterinarians and even AERC as an organization — should become more proactive and progressive in encouraging and expecting adequate treatment availabilities at rides. Early onset intravenous fluid therapy at the ride site should be considered the norm and standard for all metabolically sick endurance horses.

All treatment veterinarians working rides should be familiar with the specifics of our sport and its unique treatment situations. There are multiple reasons why aggressive, field fluid therapy is delayed: sometimes the rider wants to avoid the stigma of a treatment situation, sometimes it’s someone balking at the cost, sometimes it’s vets being too conservative, and sometimes trucking horses out seems like the better idea (when in reality this option only delays treatment even longer).

However, as expectations across the world for equine welfare are raised for all equestrian sporting events, and as we in the endurance world gather more research and information that early onset IV therapy saves lives, we can no longer afford to be passive and conservative within AERC as to our collective views on what are acceptable standards of treatment care and triage availabilities at rides.

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