Supportive care and dietary management are paramount for positive outcomes in acute colitis cases

When horses develop diarrhea, they don’t have to dart frantically to the loo like humans do, but it’s still a veritable mess. And while humans often recover uneventfully after a few days of TLC, diarrhea in horses can rapidly develop into a full-fledged, life-threatening emergency.

A primary cause of diarrhea is colitis, which is inflammation of the colon (large intestine). Complications associated with colitis develop quickly—usually within about 72 hours of disease onset—and can include severe edema (fluid accumulation in the lower limbs and abdomen), thrombophlebitis (blood clots), rectal prolapse, and the dreaded hoof disease laminitis.

“Prompt veterinary intervention and early referral to an equine hospital is always recommended for colitis cases, rather than a wait-and-see approach,” says Luis (Memo) Arroyo, Lic. Med. Vet., DVSc, PhD, Dipl. ACVIM, an associate professor at the University of Guelph’s Ontario Veterinary College, in Canada.

Even with platinum-level care and treatment, about 30% of horses succumb to colitis. If horses become dehydrated or anorexic (they’re reluctant to eat), their condition declines rapidly—within about 72 hours of the first clinical signs.

A Ticking Time Bomb

There’s more than one way to manage a colitis case. Therapy might include: 

• Treatments to stabilize the cardiovascular system (e.g., fluid and electrolyte administration);
• Addressing low blood protein levels in diarrheic patients (e.g., plasma ­transfusions);
• Neutralizing the effects of toxins in the blood—endotoxin is released by Gram-negative bacteria after they pass through the gut wall and are vanquished by immune cells—or removing them from the gastrointestinal tract (e.g., administering low-dose non-steroidal anti-inflammatories, intestinal support products such as di-tri-octahedral smectite , respectively);
• Restoring the intestinal microbiome (e.g., probiotics, fecal transplant); and
• Preventing equine gastric ulcer syndrome (e.g., gastric protectants, proton pump inhibitors) and laminitis (e.g., ­cryotherapy ).

“Every case is different, but management typically includes intensive fluid therapy and some form of antimicrobial, depending on the possible causative agent,” says Rodney Belgrave, DVM, MS, Dipl. ACVIM, staff internist and director of the internal medicine department at the Mid-Atlantic Equine Medical Center, in Ringoes, New Jersey. “The cornerstone of treatment in all of these cases, regardless of the cause, is the use of anti-­inflammatory drugs to ameliorate the effects of the endotoxemia on the body and lessen the risk of laminitis. Cryotherapy—icing of the feet as a prophylaxis (preventive method) for laminitis—is also now universally employed.”

In addition to administering medications, it’s critical you address the horse’s nutritional needs for a positive outcome.

Feeding To Heal

“Early nutritional intervention provides the patient with the ‘dietary resources’ needed for healing and expediting the recovery process,” says Gary Magdesian, DVM, Dipl. ACVIM, ACVECC, ACVCP, CVA, the Roberta A. and Carla Henry Endowed Chair in Emergency Medicine and Critical Care at the University of California, Davis.

He explains that the appropriate feeds not only provide nutrients and reestablish the intestinal microbiome but also offer diarrheic horses nutritional benefits such as:

• Minimizing gut atrophy (wasting away of the villi along the mucosal lining of the intestinal tract);
• Reducing the risk of bacteria seeping from the intestine to the bloodstream;
• Improving overall gastrointestinal function;
• Optimizing immune function;
• Healing the mucosa; and
• Expediting the recovery process.

“Many horses reduce their voluntary intake or go completely off feed when they are ill,” he says.

Horses with colitis might have a reduced appetite secondary to a lack of normal intestinal contractions (ileus), lack of blood flow to the intestines, and systemic inflammation causing general malaise and fever.

Getting an inappetant horse to eat can be as challenging as getting that horse you lead to water to drink. Magdesian says the keys to success include type, amount, and frequency of feeding.

What to feed

“I recommend avoiding long-stem mature and coarse hays such as grain hays and, instead, offering small amounts of low-bulk diets and finer-stemmed hays that are easier to digest,” Magdesian says.

Specifically, he suggests feeding a combination of:

• Complete pelleted feeds (not concentrates, which include cereal grains—oats, corn, barley, etc.—and commercially mixed feeds);
• Good-quality grass hay or alfalfa (can be chopped hay); and
• Limited pasture, as long as the horse does not have metabolic diseases that would preclude this.

“In lieu of coarse, mature grass or grain hays, complete pelleted feeds are convenient nutritious feeds that are more easily digested than hay and can aid in resting the diseased colon,” Magdesian says.

Be careful about letting your horse graze. Because of its high sugar content, grass—especially large amounts of it—can contribute to the development of laminitis or colic, especially if the horse has been off pasture.

Amount to feed

For horses that are reluctant to eat, Magdesian recommends a reasonable starting goal or target of feeding 70% of the horse’s resting digestible energy (DEr) needs. This is the “usable” energy (calories) in a feed available to the horse to drive metabolic processes. 

To calculate DEr, Magdesian uses the following formula:  DEr = (body weight x 0.021) + 0.975

So, for an average 500-kilogram (1,100-pound) horse: DEr = (500 x 0.021) + 0.975 = 11.5 Megacalories (it’s fine to round up to the first decimal point)

And 70% of the DEr = 8.05 Megacalories or 8,050 Calories.

If a commercial complete pelleted feed contains approximately 2.5 Megacalories in each kilogram of feed, then you would start feeding a 500-kilogram horse 3.2 kilograms (about 7 pounds) of that feed per day. 

“Note that this is far below an active, healthy horse’s caloric requirement,” Magdesian says. “We start with lower amounts in sick horses, especially those that are being finicky about eating (to allow for healing and recovery) and gradually increase the amount fed as they become more active and recover and, hopefully, have improved appetites.”

If you feed about a 50/50 mix of grass hay (e.g., orchard grass) and alfalfa, this combo will provide approximately 2.2 Megacalories/kilogram. Therefore, a 500-kilogram horse needs about 3.8 kilograms (about 8.4 pounds) of this mix.

Offering a complete pelleted feed with a mixture of orchard grass and alfalfa hay or even a small amount of pasture will decrease the size of each individual ration. Still, the total amount of energy should at least meet the calculated 70% DEr for your horse while he’s sick and inactive at the beginning of the feeding protocol. As the horse improves and develops an appetite and becomes more active, you should increase the amount fed.   

“Horses with colitis that have an appetite should be allowed to eat as much as they will voluntarily ingest,” says Magdesian.

“Ideally, feeds will be weighed with a kitchen scale so that they are fed accurately,” he adds. “If the horse does not begin to ingest this amount of feed over the first few days, referral to a hospital for more intensive care should be ­considered.”

How to feed

To entice your horse to eat, mix the complete pelleted feed into a warm slurry. “Start with 1 kilogram (2.2 pounds) at each feeding, and feed three to four times per day,” says Magdesian. “This 1 kilogram per feeding refers to the actual amount of feed, not including the added water.”

While some horses prefer mashes, others prefer dry feeds, so encouraging them to eat might require a bit of trial and error. 

Slowly increase the amount fed by increasing the frequency of feeding rather than the size of each offering, Magdesian advises, because anorexic horses are typically more receptive to smaller meals. Limiting meal sizes also minimizes abdominal distention, colic, and dysmotility (lack of movement through the GI tract) for those with severe colitis.

In fact, says Magdesian, overfeeding a sick horse via force feeding through a tube could be associated with a poorer outcome and could increase complications, based on studies in humans with acute colitis.

Most horses cannot be left anorexic for more than three or four days. Underweight animals or those with underlying endocrine disorders (e.g., equine Cushing’s disease/PPID, equine metabolic syndrome) require earlier intervention. Ponies, Miniature Horses, and donkeys need urgent treatment and hospital referral, even after one day of not eating, because they can develop a spiraling metabolic disorder if they don’t eat. 

If the horse does not begin to eat at least 60-70% of his calculated resting energy requirements by the third day, it’s time for your veterinarian to refer him to a veterinary hospital.

Parenteral nutrition (feeding intravenously) is an option to pursue for these referred individuals, says Magdesian.

“It can be total or partial parenteral nutrition (TPN or PPN),” he says. “Total refers to provision of all of the horse’s nutritional requirements through intravenous nutrition. (PPN) provides only partial nutrition intravenously. While TPN is quite costly for adult horses, PPN can be very cost-effective and serve as a bridge until the horse begins eating on its own.” 

Targeted Treatment Options

Most of the time veterinarians must begin treating horses with diarrhea before they know the underlying cause.

“Testing can be time-intensive, and results might not be back from the laboratory in sufficient time to help the horse,” explains Arroyo. “Treatment needs to be started before those results are back. The selected treatment is largely based on the horse’s clinical signs and basic laboratory data, such as white blood cell counts, rather than the results of specific diagnostic tests.”

Belgrave agrees, adding, “In most instances, testing isn’t performed prior to referral due to the acute nature of the disease. In some cases, if referral is not an option, testing might be performed in the field, but cost often prohibits that. Further, in most instances we have already instituted the appropriate therapy by the time the results are completed.”

Indeed, the cost of testing might be prohibitive, especially considering that treatment costs can be high.

“Nowadays we quote between $2,500 and $4,500 for three to five days in the hospital,” he says. “Testing alone can range from $350 to $1,000, depending on what’s being ordered.”

“In my hands, the cost of treating colitis cases can range anywhere from $1,500 for a mild case up to $10,000 or more for severe cases,” adds Magdesian.

If you keep your horse at a farm with other horses, Belgrave recommends identifying the causative agent to avert potential disease spread and avoid an outbreak.

“In addition, we test all admitted horses as part of our hospital biological surveillance program,” he says. “Even though the diagnosis may not be critical in managing the patient, knowledge of the pathogen (disease-causing organism) involved is an important part of maintaining the biosecurity of the hospital.”

When indicated, veterinarians have a gamut of tests at their disposal. These include bacterial cultures of feces, polymerase chain reaction (PCR) tests to detect genetic material of certain bacteria, tests for toxins, and even post-mortem analyses. Even with these tests, a firm answer isn’t always evident.

“Frustratingly, idiopathic (having an unknown cause) colitis is widely construed as the most common ‘cause’ of diarrhea in horses,” says Arroyo. “Over 50% of cases admitted to equine veterinary hospitals have no identifiable causative agent.”

A Long Road To Recovery

After diarrhea resolves, regardless of the inciting cause, transition your horse back to his regular diet slowly over two to four weeks. This period should extend well beyond the diarrhea signs dissipating. Do not rush this step, as it allows the intestinal microbiome to adjust to the “new old diet.” The intestinal microbiome has already taken a beating, and you don’t want to risk having to start over again.