An Unwanted Impact

An Unwanted Impact

A colicking horse might paw, look at his flank, and lie down and get up repeatedly.


Colic is a catchall term for almost any kind of abdominal pain, be it from gas or enteroliths, twists or blockages. The latter, which are better known as impactions, occur when consumed feed material “moves down the intestinal tract more slowly than it should, ultimately clogging the system and blocking any flow of fluid in front of it,” says North Carolina State University professor of equine surgery Anthony Blikslager, DVM, PhD, Dipl. ACVS. 

Horses are particularly prone to this colic type because their intestinal tract—particularly the colon, or the portion of the large intestine that begins with the cecum and ends at the rectum—contains a number of hairpin bends around which it’s difficult for this feed material, known as ingesta, to navigate. Those bends exist because “the colon is so long that the only way to fit it into the belly is to fold it in a couple of places,” Blikslager says. The colon also requires ample fluid to digest food properly. So if a horse fails to drink enough (about six gallons a day for an adult), his risk for developing an impaction increases.

Still, the equine digestive system works very well for horses living in natural conditions—those walking and grazing for approximately 18 hours a day, Blikslager says. It doesn’t work as well when they’re more intensively managed: stabled for much of the day, with little turnout, and receiving most of their nutrients in one or two largely concentrate feedings.

A First Responder's Perspective

As an emergency clinician and large-animal surgeon at the University of Tennessee’s veterinary hospital, Amy Plummer Weatherly, DVM, Dipl. ACVS, handled plenty of severe colic referral cases. These days, at her own Wolf River Veterinary Services, in Grand Junction, near Memphis, she’s more likely to be fielding that first worried call from a client whose horse “looks colicky.”

Weatherly says impaction colic’s clinical signs “tend to be relatively mild, not ‘throwing myself on the ground and flailing’ painful.’” Another clue is decreased fecal production: “If you’re seeing only two piles a day from a horse that normally produces four or five (and the horse has been eating normally), that feed has to have gone someplace.” Then there’s water consumption: “If a horse whose bucket normally needs two refills a day needs just one, something could be going on.”

Weatherly believes most owners who spend ample time with their horses notice these relatively subtle signs. When you think something’s not quite right with your horse, she stresses that you monitor him and call the vet if signs continue. “We’d all much rather catch the problem early and maybe avert the need for a hospital referral,” she says.

On her way to see a colicking horse, Weatherly is fine with the owner walking the animal if he’s comfortable on his feet. Owners like having something to do and, with most colics eventually diagnosed as impactions, walking helps promote motility. But do not let the horse eat, she says. “Until we get that impaction moving, we don’t want any food going in the front end.” She also doesn’t want owners administering medication until she has determined how painful the condition is and exactly what might be going on.

Upon arriving at the farm, Weatherly takes the colicky horse’s vital signs and listens for gut sounds. “But the big thing to clue me in, if I can do it safely, is a rectal exam,” she says. “With a large-colon impaction, in a rectal exam I can actually feel that there’s too much feed in the colon and that it’s dry—similar to anything from a slightly soft uncooked sausage to concrete, really dry and hard.”

Next steps depend on the horse’s pain level and the type of impaction. “If I treat the horse in the morning and sense we’ll be able to resolve the problem in the field, I may go back in the afternoon or evening and treat it again. If I think it needs intravenous fluids, which require monitoring, I’ll recommend hospitalization, but plenty of horses are fine with a couple of mineral-oil infusions, oral fluids, plus no food until multiple fecal piles come out.” If there’s no progress by that second visit, however, she advises hospitalization.

D.J. Carey Lyons

Where and How Impactions Happen

Because impactions can occur in many areas of the gastrointestinal (GI) tract, we’ll explore the different danger zones and how to prevent or manage problems.

The esophagus This passageway is the first potential site for an impaction, usually called “choke” (an esophageal obstruction, which differs from the airway obstruction that occurs in human choking). Common causes include eating too fast, having poor dentition, chewing insufficiently, and consuming poor-quality hay. As an affected animal gulps and gasps, trying to dislodge the impacted mass, a mix of saliva and food particles might spew out his nose. A veterinarian can insert a tube down one nostril to the obstruction, then flush in and siphon out water (bringing along some debris each time) until the mass clears.

The stomach Gastric impaction is possible but unusual and not well-understood, Blikslager says. An affected horse shows mild colic signs—a little pawing, a little looking back at his side, maybe a little lying down and getting up—“but remains painful despite analgesic (pain reliever) treatment, to the point that the veterinarian will advise surgery to determine the problem,” he explains. Veterinarians diagnose most stomach impactions only when surgery reveals a basketball-sized mass of ingesta.

Scientists have implicated two food items as stomach impaction causes: persimmon fruit and haylage. 

“Persimmon fruits can form a kind of gel within the stomach that is apparently very difficult to clear—though some horses get used to eating persimmons,” Blikslager says. And Finnish researchers ( tied stomach impaction to haylage (a high-moisture hay that is compressed and encased in plastic immediately after cutting and drying). 

The ileum Most impactions in this structure, located at the end of the 70-foot-long small intestine, result from one of two causes: poor digestion of coarse coastal or Bermudagrass hay or tapeworm infection. 

“With alfalfa or orchardgrass,” Blikslager says, “you may be able to feed slightly less than top quality. But with coastal hay you can’t safely feed anything less than the best—because poor- and even medium-quality hay are composed of very fine, long fibers that horses don’t chew adequately.”

Usually a horse with an ileal impaction is intermittently painful despite analgesic administration, but he’s not severely sick—although in some cases pain is intense. “Doing rectal palpation, you typically feel two or three distended loops of the small intestine on the right side, up against the cecum, which consists of a large dilated pouch); on (abdominal) ultrasound, you may also see those distended loops,” Blikslager says. “If the impaction’s been present in excess of eight to 12 hours fluid will back up into the stomach.”

He says that initially he likes to keep the horse hydrated and comfortable. In many cases the ileal impaction passes on its own. Increasing pain or stomach-fluid reflux, however, indicates a need for surgery. 

To detect tapeworm infection the veterinarian performs a blood test. The best defense against tapeworm-caused ileal impaction is deworming.

The cecum This structure can rupture (a life-threatening complication) if heavily impacted, Blikslager warns. Veterinarians must be prepared to go to surgery immediately upon cecal impaction diagnosis via rectal palpation.

Two types of cecal impactions exist. “One looks like a regular impaction,” Blikslager says, “The cecum is full of feed. We don’t fully understand why this kind of impaction occurs.” Typically, a horse shows subtle signs of colic over several days, up to as much as a week; because those signs alone could suggest a simple medical colic (treatable without surgery), using rectal palpation to identify or rule out cecal impaction is vital.

The second type of cecal impaction usually occurs in horses experiencing postoperative pain after an orthopedic surgery or other surgical procedure. In some horses the cecum becomes dysfunctional, fills with fluid and gas, and tends to rupture even earlier than other cecal impactions, usually within 24 to 48 hours of developing.

Because the causes of cecal impaction aren’t clear, veterinarians recommend simple good-management practices as prevention: provide your horse plenty of quality forage, free-choice palatable water, regular turnout, and routine veterinary and dental care.

Large colon The majority of impactions occur here, at the site of those hairpin bends: the pelvic flexure (see illustration on page 56) and the transverse colon. Blikslager says veterinarians can manage these horses medically despite their pain. His first remedy might be to “lube up” the intestine by administering mineral oil using a nasogastric tube.

“Typically—and as long as the animal’s comfortable—we’ll monitor it for three to five days, continuing to treat with fluids and laxatives while deciding whether/when to recommend surgery,” he says. 

Prevention measures include providing quality forage and encouraging water intake. Blikslager also recommends that owners feeding concentrate choose a pelleted feed that’s low-starch, high-fiber, and supplies energy from fat.

Small colon This last part of the GI tract is where fecal balls are made; as that happens, the body tries to absorb and retain fluid. In some cases the resulting manure is too solid to be passed easily. Miniature Horses are particularly susceptible to these impactions. “We don’t know why,” Blikslager says, “except that it might be related to their inadequate chewing of feed. Some Miniatures’ teeth don’t align well.”

Blikslager notes that medical treatment alone hasn’t been very successful in clearing small-colon impactions. “Once the small colon is severely distended, and if signs of pain continue, surgery is the best option,” he says.

Take-Home Message

Impaction colic can be a life-or-death problem. The best defense against it is providing your horse good nutrition and managing him responsibly: offering quality forage, plenty of drinkable water, regular exercise, and a consistent routine, and making any dietary changes gradually.

About the Author

D.J. Carey Lyons

D.J. Carey Lyons is a lifelong resident of Chester County, Pa. She also has written for USDF Connection, Practical Horseman, Equine Images, and Dressage & CT.

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