Flank-watching or -biting, pawing, trying to roll, an elevated heart rate, a lack of gut sounds or bowel movements. While these signs and others are pretty clear, common indicators your horse is colicking, what they don’t tell you is the type of abdominal pain he’s experiencing. Within that cavernous abdomen are a number of organs, with which a variety of things can go wrong. A piece of intestine can twist, a foreign object or lump of ingested material can cause a blockage, and infectious organisms can inflame the gut.
Depending on a colic’s cause, treatment steps and prognoses can vary widely. So in this article we’ll break these cases down by type—nonstrangulating, strangulating, and inflammatory. We hope you won’t be faced with this potentially life-threatening condition, but if you are you’ll have a better understanding of what your veterinarian is describing and the road that lies ahead.
A nonstrangulating obstruction (NSO) is a physical blockage or narrowing of some part of the gastrointestinal (GI) tract that prevents fluid and digesta from flowing through normally. These colics are by far the most common—Diana Hassel, DVM, PhD, Dipl. ACVS, ACVECC, associate professor of Equine Emergency Surgery & Critical Care at Colorado State University, in Fort Collins, estimates they make up at least 80% of colic cases in most regions of the country.
Veterinarians further subcategorize these obstructions based on their location and cause, including:
These are some of the most common NSOs and occur frequently in the large colon, particularly at the hairpin bend around the pelvic flexure and the bend into the transverse colon. Forages and fibers simply get lodged in these areas sometimes.
Impactions can also occur in the ileum, which is the final part of the small intestine. “Ileal impactions occur almost exclusively in adult horses in the southeastern United States, from North Carolina down to Florida over to Texas,” says Anthony Blikslager, DVM, PhD, Dipl. ACVS, professor of equine surgery and gastroenterology at North Carolina State University, in Raleigh. While veterinarians don’t know the exact reason for this regional risk, he says feeding coastal Bermuda hay—which is fine and stemmy—in these areas might have something to do with it.
Horses also experience small colon and stomach impactions, though these are less common.
Horses eating off sandy soils can ingest enough sand that it accumulates in the large colon.
This obstruction is seen almost exclusively in weanlings, which tend to carry ascarid parasites when not dewormed regularly. Colic can occur shortly after a youngster with a heavy ascarid burden gets dewormed—the mass of dying parasites can cause an obstruction as it makes its way through the small intestine.
These mineral stones can develop in the large and small colon, requiring surgical removal if they grow large enough to cause a blockage. Blikslager says they tend to occur more frequently on the West Coast than the East, with California horses being the most severely affected.
Left or right dorsal displacement of the large colon
The horse’s large colon is essentially suspended from the upper body wall at a single attachment point, allowing it to move around the abdomen. Rarely, it shifts to the point it gets trapped against other organs, causing an obstruction.
“The majority of nonstrangulating obstructions we’re able to successfully manage medically (i.e., with pain relief, intravenous and oral fluids, laxatives, nasogastric tube, and walking),” says Hassel. “However, some of them will not respond to medical therapy, in particular those cases with displaced colons.”
Stomach impactions or intestinal obstructions that are so firmly impacted they won’t loosen with medical therapy are almost always surgery candidates, adds Blikslager.
Fortunately, the prognosis for most nonstrangulating colics is quite good, because the bowel doesn’t usually get damaged. Long-standing impactions, however, can apply so much pressure on the intestinal wall that the bowel begins to degenerate. Blikslager recommends keeping an eye out for signs of potentially fatal endotoxemia (e.g., abnormal-colored gums, delayed capillary refill time when you press on the gums, and high protein and white blood cell counts in the abdominal fluid) in these cases.
Strangulating obstructions (SO), while not as common as nonstrangulating, are far more serious and always require surgery. They occur when part of the GI tract twists or gets entrapped, cutting off blood flow to that region. Types of strangulations include:
Small intestine volvulus
With a volvulus, a piece of intestine twists around itself. Many volvulus colics occur in the small intestine, often involving the ileum (middle portion) and the jejunum connected to it, simply because of that organ’s anatomy.
Hassel explains that as you travel from the start of the small intestine to the end, its mesentery (the blood-supplying membrane that connects it to the body wall) gets increasingly longer. “The jejunum and ileum are the most commonly affected, probably related to the length of that mesentery and its ability to move more around the abdomen,” she says.
Because of that long mesentery (the horse’s small intestine is about 70 feet long) the bowel can more easily end up someplace it’s not supposed to be, says Blikslager. One of those places is in the epiploic foramen—a narrow opening in the forward part of the abdomen. The resulting severe and difficult-to-correct SO is called an epiploic foramen entrapment.
Less commonly, the small intestine can also become trapped in a tear in the mesentery—called a mesenteric rent—or a tear in the gastrosplenic ligament that runs from the spleen to the stomach, called a gastrosplenic entrapment.
Large colon volvulus
The large colon, with only one attachment to the upper body wall, has the ability to turn around on its own axis and become twisted. This is one of the most common types of volvulus and fatal forms of colic, says Blikslager, and tends to occur most frequently in broodmares when they foal or right after. Veterinarians still don’t know exactly why it happens, though physiological, management, exercise, nutritional, and microbiome (microorganisms and their interactions in the gut) changes are all possible causes, he says.
Fatty lumps called lipomas can form along the mesentery; these can grow with a stalk or stem and end up wrapping around the intestine. This colic type is most common in geldings age 15 and older and typically occurs in the ileum or jejunum.
Rarely, horses experience intussusception in the colon or small intestine, “where a piece of bowel rolls inside the adjacent bowel, kind of like a sock turning inside out, and it pulls the blood supply with it,” Blikslager says.
Again, the treatment for any of these strangulations is surgery. The horse’s prognosis depends on the duration of the colic, the severity of the strangulation, and the amount of gut entrapped, says Hassel.
“About 85-90% of horses in relatively good condition—maybe just a little dehydrated, elevated heart rate, beginnings of abnormal gum color—will make it through surgery and all the way to hospital discharge,” says Blikslager. “While we can get almost all of them out of the hospital, one postoperative complication in particular can reduce their survival. That’s adhesions, where the bowel, because it’s been manipulated and injured during the strangulation, becomes inflamed and sticky.”
He says he gives horses with small intestine SOs a 60-65% long-term survival rate at that point. For horses with large colon volvulus, by the time it gets diagnosed and they travel three hours (the average travel time for colic cases to NC State) to the hospital, the prognosis for survival to discharge is closer to 40 or 50%, he says.
Cases owners and veterinarians catch immediately—and can operate on before the affected portion of the bowel dies—not only have a much better prognosis for survival (greater than 80%, says Hassel) but also cost significantly less to treat.
“They tend to have fewer complications because they don’t have that dead, toxic bowel trapped in them for any period of time,” she says. “That changes the whole systemic response and makes them less prone to complications. Once the bowel dies, the treatment is removal of the affected segment.”
She says her clinic typically quotes owners between $7,000 and $15,000 for a colic surgery.
Colics due to inflammation are usually caused by microorganisms such as bacteria, molds, and viruses. The two most common are:
This infection and inflammation of the colon can be quite severe and is typically associated with mild to explosive diarrhea. It can result from a variety of microbes, including Salmonella, Clostridium, Neorickettsia risticii (which causes Potomac horse fever), and coronavirus. Veterinarians don’t know the cause of most colitis cases, however, because of the sheer number of organisms that can induce inflammation, says Blikslager.
“We often call acute cases ‘colitis X,’ because we don’t really have a good underlying explanation for the cause,” says Hassel. “There are probably many pathogens causing colitis that haven’t been identified, and that’s why in the majority of cases we don’t ever find a cause—just lots of inflammation in the colon and lots of diarrhea.”
Life-saving treatment for these horses is often aggressive and expensive and includes lots of fluids, colloid support (used for fluid replacement), and sometimes antibiotics.
“Another really important therapy we use a lot is DTO (di-tri-octahedral) smectite, which helps bind some of the toxins present in the gut to reduce their absorption. These absorbed toxins cause a lot of the clinical signs when horses are very sick—very high heart rate, red mucous membranes, and a high risk of foundering,” says Hassel.
This condition, also called duodenitis/proximal jejunitis or proximal enteritis, causes inflammation of the small intestine. The result, says Hassel, is “fluid accumulation in the small intestine and lack of progressive motility, or movement of the fluid downstream. What happens is that fluid will back up into the stomach, and so horses will get painful as the stomach distends with fluid.”
Again, many organisms—most of which are unknown—can be associated with this condition, including Salmonella and Clostridium, along with Fusarium mold. Most horses respond well to supportive care such as fluid therapy, passing a nasogastric tube, and decompression of the stomach.
Our sources agree that there appear to be regional differences between enteritis cases. Out West, for instance, they seem to be more mild than in the Southeast.
The prognosis for horses with colitis or enteritis depends on the degree of inflammation. “Some horses we’ll lose within a day or two, because it’s hard to keep up with the fluid and protein loss, whereas others do much better,” says Blikslager.
These are just some of the more frequently encountered and discussed colic causes and types. Others include stomach ulcers, infarctions (blood clots cutting off blood supply to the bowel), peritonitis (inflammation of the abdominal lining), and a whole host of conditions that mimic colic. The equine GI tract is a complex beast, and many things can go wrong. With good management and nutrition, however, you can help keep colic at bay.