Dr. Tania Sundra

25 May 2020

Hindgut Ulcers – Fact or Fiction ?

The term “hindgut ulcers” has been bantered around a lot in recent years. Almost every horse owner knows someone who’s horse was “diagnosed” with hindgut ulcers.


What Exactly is the Hindgut of the Horse ?

The equine hindgut or large intestine consists of the following segments : the cecum, the large colon, the small colon and rectum. The hindgut in horses is approximately 7.5 to 8.0 m long. A major function of the large intestine is retention of fluid and feed to facilitate important microbial digestion. Volatile fatty acids are also produced in large quantities in the hindgut.

The Background of Hindgut Ulcers

Much of the current theories of hindgut ulcers are largely based on a study which was done in 2005 by Frank Pellegrini in which he “diagnosed” colonic ulcers in 44% of non-performance horses and 65% of performance horses during post-mortem exams at an abbatoir in Texas. Whilst these numbers might seem pretty convincing at first glance, the study is not robust, is lacking a lot of important information and the findings have never been replicated in future studies. Some of the important information missing from this study is that we know nothing about the veterinary history of these horses, how they were managed (worming/feed etc.) and whether they received any anti-inflammatory medications prior being sent to the abbatoir. The reason this is so important will become clearer in a few more paragraphs. The author of this study was also one of the founders of Succeed – a company which sells the fecal occult blood test to “diagnose” hindgut ulcers as well as the “treatment” for horses who test positive.


Current Research
A more recent (2017) study, performed at the University of Glasgow looked at the gross pathology of lesions on the mucosal surface of the equine large intestine. The large intestine of these horses was examined immediately following euthanasia and they found that colonic ulceration was only present in 21% of horses. Small strongyles (cyathastomins) and tapeworms were the cause of more than 50% of the lesions, a small number was caused by sand and about 25% were due to unknown causes. There are no known conflicting interests in the authors of this study.

More than 50% of colonic ulcers were parasite related.

A more “traditional” cause of colon ulceration is due to a condition known as right dorsal colitis (RDC). RDC occurs predominantly due to prolonged administration of non-steroidal anti-inflammatory (NSAID) medications (bute/flunixin) at high doses. These drugs stop the cycle of inflammation by blocking the production of prostaglandins which cause inflammation. However, prostaglandins are also involved in regulating blood flow and mucus production in the gastrointestinal tract – which are protective mechanisms. So not only do these drugs block the “bad” part of prostaglandins, they also block the “good” part of prostaglandins, resulting in the development of ulcers. Might those horses at the Texas abbatoir been given large doses of NSAID’s prior to being sent there ? In reality, we will never know, but it’s worth keeping in the back of our mind. RDC is diagnosed largely on clinical signs, history of NSAID use, bloodwork as well as abdominal ultrasound of the right dorsal colon which may show thickening of the wall which is consistent with inflammation. Treatment of RDC involves discontinuation of NSAID’s, medical therapy and feeding of a lower fibre diet to allow the hindgut to “rest”.


My Two-Cents’ Worth

Hindgut ulcers almost certainly exist in horses. Their prevalence, however, is probably much lower than some would have you believe. We have yet to develop an accurate ante-mortem test for hindgut ulcers with good sensitivity and specificity and that has undergone vigorous independent validation. So where does that leave us? Well, one thing we can do, is implement a targetted deworming plan in order to rule out the occurrence of parasites as a cause for colonic ulcers and limit the issues surrounding parasite resistance. We should also use NSAID medications like bute and flunixin judiciously and never outside the labelled dose without consulting your veterinarian first.

Whilst it would be foolish to completely disregard the earlier work that has been published, I strongly believe there are ethical concerns when people are “diagnosing” a condition that cannot be proven and then selling a treatment for a condition who’s efficacy cannot be disproven.


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References :

Kerbyson, NC, Knottenbelt, DC, Hotchkiss, J & Parkin, TDH 2017, ‘Idiopathic Colonic Ulceration: Prevalence, Gross Pathology and Clinical History in 56 Horses’, Equine Veterinary Journal, vol. 49, no. S51, pp. 13-16.

Pellegrini, FL 2005, ‘Results of a Large-Scale Necroscopic Study of Equine Colonic Ulcers’, Journal of Equine Veterinary Science, vol. 25, no. 3, pp. 113-117.