Page 82 - December 2021

EQUINE HEALTH
RIGHT IN DORSAL OH
COLITIS ESR S
Hby Heather Smith Thomas
orses occasionally develop inflammation and ulceration of the gut lining, most commonly in the stomach (gastric
ulcers). Colitis, or inflammation of the colon, is rarer, but can be very serious. For some reason, this problem tends to occur more in the right dorsal colon.
Dr. Anthony Blikslager, Professor of Equine Medicine and Surgery, College of Veterinary Medicine, North Carolina State University, says that in his experience, right dorsal colitis is exclusively associated with non-steroidal anti- inflammatory drugs. “The only cases I’ve seen have been triggered by use of phenylbutazone. We don’t know why the right dorsal colon is affected and not the rest of it. One theory is that the colon contents (digested food moving through) are changing at that point near the end of the colon. The colon is doing less fermentation by then, and more absorption
of water. This might mean it is concentrating something within the food or changing the microbial population,” he says.
“There is also debate whether there is change to the blood circulation (supplying the colon) at that point. Perhaps that part of the gut is predisposed to problems because it’s a
bit more sensitive to changes in circulation. Prostaglandin (especially prostaglandin E2, or PGE2, which is thought to be protective in keeping the gut lining healthy) is inhibited by phenylbutazone. One of the things that PGE2 does is dilate blood vessels, under normal circumstances. Maybe the blood flow is a little less in the right dorsal colon (for some reason) than in other parts of the colon. Then if you remove prostaglandins (by using phenylbutazone) the crucial blood circulation to that area might become compromised.” This would affect blood flow to the gut
lining and hinder its mucus production. “The gut lining is very sensitive to changes in blood flow because of its high demand for oxygen, which helps energize the necessary enzymes and transporters. It can’t go without oxygen for very long,” explains Blikslager.
“Probably the ultimate scenario, regarding whether a horse might develop right dorsal colitis, would be a combination of factors. One factor would be the individual horse. If that horse is extremely stressed for some reason (which can change things in the gut), it might be more vulnerable to this problem. Each horse also has its own individual microbial
population. Some will have a few more ‘bad bugs’ than other horses. Then when you add phenylbutazone into that picture, and it slightly reduces the blood flow to the gut, this might be enough to push that horse over the edge in terms of health of the lining,” he says.
This is a similar to what causes ulcers in humans. “In people, we used to think that ulcers were purely acid caused, related to diet. Now we understand that it is also related to individual factors, in certain people. It’s not just diet, although it plays a role. It’s also bacteria (particularly Helicobacter pylori). Problems in the gut are usually due to multiple factors. Inside the gut there is always a delicate interaction with the contents (food) and the lining, and the overall influence of the body on what’s going on in the gut,” he says.
“Fortunately, right dorsal colitis is rare in horses. It used to be thought that this disease was due
to an overdose of bute, but this is not necessarily the case. It can also be caused by normal doses.” Many horses with arthritis that are on very low maintenance doses to keep them comfortable do just fine, but some horses can’t tolerate long-term bute administration.
“We once had a horse here in the hospital that had an elective orthopedic procedure and
80 SPEEDHORSE December 2021