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SOME THOUGHTS ON COLIC

James R. Rooney, DVM

"Perhaps these ideas might i be of use to those doing L research on the causes of i colic..."

Somewhat in the spirit of the letters in the New England Journal of Medicine, I submit the following for your consid- eration. Since this is speculative, I don't really think it should be a paper as such, but perhaps these ideas might be of use to those doing research on the causes of colic in horses. I have no way to pursue the ideas and can only hope someone can.

Torsion of the colon, the entire ascending colon to include the right ventral, left ventral, left dorsal and right dorsal colon, appears now to be a rather common cause of colic in middle aged horses. A number of cases were reported recently, for instance, in the JAVMA under the unfortunate title of strangu- lated volvulus.

I first began to see these cases in the 1960s but only a few cases per year and mentioned the condition in my book on autopsy of the horse, perhaps the first mention in the literature of the condition. Torsion of the colon was described in the olderGerman pathology literature but always involved the left dorsal and ventral colon only, the twist occurring at the sternal/diaphragmatic flexures. I have seen very few cases of this type of torsion, fewer indeed than of torsion of the whole ascending colon. The ones that I have seen of this type were clearly associated with parasitic emboli in the dorsal and ventral colic arteries at the site of twist. Good parasite control was coming in when I began to do horse postmortems and that may explain why torsion at the sternal/diaphragmatic flexures is uncommon these days but was of some note in earlier German compendia of causes of fatal colic.

With torsion of the ascending colon, worms or other obvious causes have notbeen seen but atrophy of the right lobe

Author's address: Maxwell Gluck Center, University of Kentucky, Lexington, KY 40505

of the liver is common, though I don't believe inevitably present. Also, atrophy of the right lobe is reasonably common in the older horse without torsion of the colon, so atrophy might well be predisposing in many cases but not primary.

A possible pathogenesis/hypothesis I come up with is gas formation in the right ventral colon, floating that portion up medially alongside the right dorsal colon. In this position a peristaltic wave could cause torsion of the entire ascending lportion - a clockwise rotation as seen from the rear in the standing horse. It is difficult to evaluate this point at postmortem because of the significant accumulation of gas which occurs with the ileus associated with torsion. Some surgeons have in- dicated that they see marked gas formation in the right ventral colon without significant gas in the right dorsal when they are into the belly fairly early in the clinical course. That supports, but of course does not establish, the hypotheses.

Since it appears that torsion of the whole ascending colon (as opposed to torsion of the left ventral and left dorsal seg- ments only) is historically quite recent, my only postulate is that changes in feeding practices might be related. One doesn't like to simply blame feeds and feeding for whatever goes wrong, an all too common practice. One might consider, however, what fermentable feed, bolus-fed, might be relevant for the proposed excess gas formation in the right ventral colon. It is certainly the case that "richer" feeds are available to horses these days than in the era of timothy hay. The atrophy of the right lobe of the liver may well be predisposing, but that alone does not explain the torsion.

I hope you may see you way to publishing this as a letter to the editor or however you wish. Perhaps a horse might be helped one day.

296 EQUINE VETERINARY SCIENCE