Colitis is one of those “under the radar” conditions. It occurs infrequently enough to rank below a twisted gut, laminitis and similar conditions on the list of horse owner concerns, but it’s not exactly rare. You probably don’t need to worry about it too much. But you also probably should know more about it than you do.

Essentially, colitis is a form of colic. And the early signs of the condition are indistinguishable from those of other types of digestive upset: loss of appetite, lethargy, discomfort, elevated respiratory rates and a rapid heart rate.

But colitis affects a specific portion of the horse’s digestive system and that gives it some particular characteristics. “Colitis is an inflammatory condition of the colon, which is the large part of the intestine of the horse,” explains Gary Magdesian, DVM, DACVIM, DACVECC, a professor at the University of California, Davis School of Veterinary Medicine.

In a healthy horse, the large and small colon extract water and nutrients from digested food, allowing firm stools to form as ingesta passes through. The disruption of that process leads to the primary sign of colitis—watery, persistent diarrhea. In contrast, says Magdesian, “horses with other types of colic generally don’t develop diarrhea, and most—especially those with a blockage—pass little to no feces.”

The large intestine also has another important function, protecting the body from gut bacteria and bacterial byproducts that contribute to or result from digestion. “Under normal circumstances, the colon serves as a barrier protecting the horse from gut bacteria and their toxins. It keeps him or her from getting sick,” says  Magdesian. “When there’s inflammation in the colon wall, it loses that barrier function, and the horse can get quite ill from the bacterial toxins that get across the gut wall and into the bloodstream.”

When there’s a fever

That’s where the other identifying characteristic of colitis—fever—comes in. “Fever is one sign that helps to differentiate primary colic from colitis,” Magdesian says. “Fever is common with colitis and not as common with impactions, strangulating lesions or other forms of colic. Also, when you do bloodwork on horses with colitis, the white count will often be low. Those are a couple of clues to point to the possibility of colitis in that early phase.”

So, while initially it may be challenging to distinguish colitis from other types of colic, a swift and accurate diagnosis is important—and even potentially life saving. Erin Byrne, DVM, Dip. ACVIM, Internal Medicine Specialist at the Alamo Pintado Equine Medical Center in Santa Ynez Valley, explains why: “Whatever the causative agent—if it’s Clostridium, Salmonella or something we haven’t identified—when horses get inflammation of the colon, a lot of endotoxins are released into the bloodstream,” she says. “Then the body kind of freaks out, trying to attack those toxins and get them out of the bloodstream. Then it can affect other organs.”

Research suggests that most untreated horses with acute colitis die or are put down. But with prompt treatment, most horses recover within one to two weeks.  “With a lot of intensive care, I’ve seen about 80 percent survival,” Magdesian says. “But many of these horses are in the ICU, getting 24-hour round-the-clock care. Out in the field and left untreated, colitis would be highly fatal.”

Primary causes

Of course, not all horses with sloppy manure have colitis. Magdesian emphasizes that brief bouts of diarrhea related to trailering, competition or other potentially stressful events in a horse’s life are normal. “Transient diarrhea is not the same as colitis,” he says. “If you looked at the histology of the bowel of horses with transient diarrhea, there’s no inflammation. It’s just the nervous system causing temporary hypersecretion and changes in motility in the hindgut that causes diarrhea. They defecate out more water, but that’s not a form of colitis.”

Nonetheless, those stressors, along with a host of other management, environmental and lifestyle factors, can lead to the development of colitis in horses. Common causes of colitis include:

Medications

Certain drugs, particularly antibiotics and non-steroidal anti-inflammatory drugs (NSAIDs) can disrupt the normal microbial balance in the horse’s gut, leading to colitis.

Pathogens

Salmonella and Clostridium bacteria are common causes of colitis, as is equine coronavirus. Colitis is also a common complication of Potomac horse fever, which is caused by Neorickettsia risticii or findlayensis bacteria. 

Prolonged or extreme stress

Stressful events such as long-distance transport, changes in environment or deviations from routine can disrupt gut function and lead to colitis. 

Internal parasites

Infestation with strongyles (especially small strongyles) and other worms can contribute to colitis,  particularly in  older horses or those whose health is otherwise compromised.

Toxins

One of the effects of the ingestion of poisonous plants is colitis. 

Feeding related

Switching too quickly to a new feed can disrupt the horse’s digestion and contribute to colitis. Other feed-related causes include grain overload, ingestion of moldy or otherwise contaminated feed and the accumulation of sand in the horse’s bowel (sand colic with secondary colitis).

Autoimmune reactions

Equine inflammatory bowel disease (EIBD)  and other health issues can also contribute to colitis. 

Treatment options

Like many other diseases and conditions in horses, colitis is most treatable in its earliest stages. “As soon as a horse owner sees depression and not eating, especially with a fever, that definitely warrants a vet call,” Byrne warns. 

Magdesian agrees. “If horses with colitis are not treated early they’re at a much higher risk for complications, including laminitis or founder and clotting in major blood vessels such as their jugular vein or colonic vessels. They can develop secondary infections like pneumonia,” he says. “The earlier we get to treat them, the fewer of these complications arise. If a horse with colitis goes without treatment, he can develop kidney injury and renal failure. So early treatment helps ward those things off.”

In addition to starting treatment, your veterinarian may institute a quarantine to keep the causative organism from spreading to other horses on the property. Noting that some forms of bacterial colitis are highly contagious, Magdesian emphasizes the importance of quarantine, even before the cause of colitis is identified. “There’s always a delay from when you start treatment to when you get results of diagnostic testing back. You always assume it’s contagious so you’re ahead of the game,” he says. “You don’t want to find out three days later that it was salmonellosis and you didn’t quarantine the horse.”

Treatment focuses on addressing  inflammation and infection (if  present) and attempting to restore  the balance in the microbiome.  Common measures include:

medications, specifically anti- inflammatories and analgesics

antibiotics if a bacterial pathogen is suspected or identified 

fluids, biologics and nutrients  delivered intravenously: “IV fluids are one of the most important parts of treatment  of colitis because these horses get extremely dehydrated very quickly due to large  volumes of diarrhea,” says Magdesian. Administering plasma can be particularly helpful, says Byrne.  In addition, nutrients may be administered via IV to provide support if the horse isn’t eating.

heparin, an anticoagulant: “Anything we can help with blood flow to the colon— that’s very important,” says Byrnes

smectite, a clay-like product that binds to toxins and assists in excreting them from the body

gastroprotectants like omeprazole (brand name Gastrogard) and other  agents that can protect the stomach  and intestines

prebiotics and probiotics, although research into the effects of these products is scant. Many veterinarians believe that supplying these nutrients and beneficial organisms can support the growth of beneficial bacterial and help restore balance to the intestinal microbiome.

What recovery can look like

With appropriate and aggressive treatment, most horses with colitis can recover within a few weeks. However, several factors can affect colitis prognosis, including the invasiveness and virulence of any causal organisms, and the general health of the horse. “We’ve definitely had some horses with colitis that, no matter what we’re doing, it goes really quick—24 or 48 hours and we’ve lost them,” says Byrne. “But the majority of them do survive with a lot of medication, time, effort and people sticking with them.”

Complications, particularly endotoxemia and laminitis, are a major concern with colitis. “Unfortunately, sometimes you get horses past the colitis and then laminitis develops, which is so sad,” says Byrne. “It’s not fair because you think you won the battle and then they start showing soreness to their feet. We have a lot more to learn about how to prevent laminitis in these horses.”

Prevention

Fortunately, when it comes to reducing your horse’s risk of developing colitis, the primary measures are part of any sensible horse care routine. These include:

maintaining regular parasite control

minimizing exposure to Salmonella and other organisms by implementing pest control on your property to reduce rodent populations and other potential carriers.

supplying clean drinking water

staying alert for toxic plants in pastures or near paddocks

reducing direct physical contact with other horses at events or at other barns

adhering to biosecurity measures—disinfecting surfaces and avoiding shared buckets or equipment—on the road

preventing sand ingestion by feeding  on mats

administering pre/probiotics, although there are some unknowns about effectiveness

avoiding sudden diet changes

quarantining any horse that develops sudden diarrhea and calling your veterinarian as soon as possible

keeping your horse’s vaccinations up to date, particularly against Potomac horse fever if it’s in your region

monitoring your horse carefully when he receives antibiotics and NSAIDS, such as phenylbutazone (“bute”) or  flunixin meglumine (Banamine). 

Prevention is key

Like so many other problems that  can befall horses, colitis is a condition you’re better off preventing  than trying to treat. Even a minor  case can take a toll on a horse’s health  and your budget, and severe cases are  life-threatening.       

Fortunately, by keeping up with the basics of good horse care, including  vaccinations and other preventive measures, sensible hygiene at home and on the road, careful management of your horse’s diet, and monitoring of his response to medications, you can reduce your horse’s risk of colitis. And should he develop the condition, prompt action can go a long way toward heading off the worst potential outcomes.