Intestinal Aspects of Laminitis

How laminitis starts and proceeds through the horse's body is being charted by Jonathan Elliott, MRCVS, PhD, and other researchers at the Royal Veterinary College (RVC) in the United Kingdom. Elliott spoke at a conference organized by the Veterinary Advisory Committee of the Horserace Betting Levy Board in England this spring, where he outlined the RVC's progress in charting a pharmacological vision of the laminitis disease process. His recent studies detailed how fermentation factors in the equine gut could cause a reduction of blood flow to the foot.

Through some as-yet defined disease process, laminitis reduces blood flow to the sensitive laminae of the foot and deprives the tissues of oxygen and nutrients. According to the RVC's vision of laminitis, the return of blood to the diseased tissues activates enzymes that destroy the bonds in the laminae and causes further destruction of the tissue. Disruptive enzyme attacks can start in two places in the horse: Within the circulating blood itself or in the digestive tract. The enzymes produce unique "mediators" that take over normal regulatory functions in blood platelet cells and nerve endings.

Elliott detailed evidence of a reduction in hind gut (cecal) pH following carbohydrate overload, generally believed to be the leading factor in the onset of laminitis in otherwise healthy horses. Carbohydrate overload has also been associated with an increase in amine (an organic compound containing nitrogen) production in the gut.

Changes in the gut's acidity were linked to simultaneous changes in the permeability of the gut; a drop in pH would allow more of the excess amines into the bloodstream. Elliott's challenge was to connect the amines crossing into the bloodstream with the damage to the hoof wall.

The RVC's experimental model used a low dose of tryptamine and phenylethylamine; after administration, researchers recorded an associated reduction in blood flow to the feet by Doppler ultrasound. At the same time, there was no recorded change in arterial blood pressure or heart rate.

When the infusion was discontinued, normal blood flow returned to the feet. However, a mediator identified as 5-hydroxytryptamine (or "5-HT"), which is present in blood platelets, increased in the circulation.

Elliott's research group contends that they have successfully supported the hypothesis that gut amines can and do selectively reduce blood flow to the hoof wall and play a role as triggers in the laminitis disease process. They will now seek supporting field documentation and work on how the amines and circulating 5-HT mediator might actually cause the damage to the foot.

About the Author

Fran Jurga

Fran Jurga is the publisher of Hoofcare & Lameness, The Journal of Equine Foot Science, based in Gloucester, Mass., and Hoofcare Online, an electronic newsletter accessible at Her work also includes promoting lameness-related research and information for practical use by farriers, veterinarians, and horse owners. Jurga authored Understanding The Equine Foot, published by Eclipse Press and available at or by calling 800/582-5604.

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