Right dorsal colitis is a gastrointestinal disease of the horse that can be challenging to prevent and treat. Anje Bauck, DVM, PhD, Dipl. ACVS, clinical assistant professor of large animal surgery at the University of Florida’s College of Veterinary Medicine, in Gainesville, recently turned to comparative medicine to try to improve our understanding of the condition. She presented her research at the 2022 American Association of Equine Practitioners (AAEP) Convention, held Nov. 19-22, in San Antonio, Texas.

What Is Right Dorsal Colitis?

Right dorsal colitis is a type of colitis (inflammation of the colon) observed in the horse’s right dorsal colon. It’s commonly documented in performance horses and is associated with clinical signs of recurrent low-grade colic, chronic diarrhea, low blood protein levels, and weight loss.

Veterinarians believe non-steroidal anti-inflammatories (NSAIDs) such as phenylbutazone (Bute) play key roles in the disease’s development.

“Presumably, NSAIDs predispose horses to right dorsal colitis by suppression of prostaglandin secretion,” said Bauck. “Prostaglandins are critical for maintaining the protective mechanisms of the mucosa in any tissue, and this includes bicarbonate (an anion) and mucous production.”

The colon is where the horse’s body ferments feedstuff, which produces a large volume of volatile fatty acids that need to be neutralized by buffers such as bicarbonate to protect the mucosa, she explained.

Study Results

Bauck aimed to examine one physiologic mechanism influenced by prostaglandin—bicarbonate secretion—and how NSAIDs might affect it. In her study she collected tissue samples from the right dorsal and right ventral colon of 10 horses undergoing surgery. She measured bicarbonate secretion and changes in pH levels in all samples, then evaluated the effects of phenylbutazone on four of those horses’ samples.

“We found that when comparing baseline bicarbonate secretion between the dorsal and ventral colon, the dorsal colon had greater bicarbonate secretion than the ventral colon under normal conditions,” said Bauck. “With Bute, that secretion was significantly reduced.”

She said this confirmed the right dorsal colon does, in fact, have robust bicarbonate secretion that decreases in the presence of an NSAID such as phenylbutazone.

Comparing Diseases Among Species

As part of her research, Bauck also wanted to see if she could learn from any similar naturally occurring diseases in other species. In reviewing previous studies, she noted that cystic fibrosis—a genetic disorder that causes breathing and digestive issues in humans—is also associated with a bicarbonate deficiency.

“We know impaired anion secretion can result in disease in other species,” she said. “We’re simply noting that cystic fibrosis in people and lab animals is caused by a failure of anion secretion in the lungs, pancreas, and especially the intestines, with similar intestinal lesions to right dorsal colitis in horses.”

What’s the significance of this similarity? Bauck said it might open the door to treatments veterinarians have not investigated for right dorsal colitis specifically, such as feeding horses oral sodium bicarbonate (baking soda).