Learning About Laminitis

The 14th annual Bluegrass Laminitis Symposium, hosted Jan. 25-27 by R.F. (Ric) Redden, DVM, and his wife, Nancy, of the International Equine Podiatry Center, unveiled many recent advances in the mechanisms of laminitis, navicular disease, and various shoeing and trimming methods.

This year, symposium attendees were treated to seminars on wild horse foot physiology and four-point trimming with Redden; new information on hoof microanatomy and laminitis trigger factors with Chris Pollitt, BVSc, PhD; biomechanical analysis of hoof and limb forces with Alan Wilson of the Royal Veterinary College in England; laminitis prognosis and pain management with David Hood, DVM; radiographic and photographic techniques, and much more.

One of the biggest revelations of the symposium was Pollitt's presentation on his laminitis work at the Australian Laminitis Research Unit, in which he discussed carbohydrate overload-induced laminitis. It seems likely that carbohydrate overload provides an very favorable environment for Streptococcus bovis bacteria in the hindgut, in which case its population explodes (doubling about every 12 hours). With this abnormally large bacterial population, Pollitt theorizes that the bacterial toxin weakens the mucosal barrier of the gut, allowing the toxin to reach the bloodstream and thus the feet, where it activates enzymes that degrade the laminar attachment of the hoof to the foot in vitro. Pollitt has found that virginiamycin antibiotic administered before carbohydrate overload prevented laminitis in many cases, and that some enzyme inhibitors minimize the damaging effects of the S. bovis-activated enzymes.

"Perhaps this is why it's eluded us for so long," Pollitt concluded. "It looks like a normal process that has gotten thrown out of balance."

A field study presented by Matthew Frederick, an American Farrier's Association certified farrier, found success with treating refractory (chronic) laminitis with pergolide mesylate, which is commonly used to treat hormonal imbalances in Cushing's disease.

Redden discussed a new curved shoe he has been using on severely lame horses, and used the shoe on several horses in a live demonstration. The shoe moves breakover much farther back toward the heels than any shoe currently on the market, and it leaves an "air space" under the heels so the horse can load the foot however it is most comfortable.

Wilson's biomechanical studies used the angle of the hoof measurements and force plate data to calculate force on the navicular bone without invasive monitoring. Wilson found that in normal horses, tension of the deep digital flexor tendon (DDFT) and thus pressure on the navicular bone spikes early in the stride, drops, then increases to the maximum fairly constantly until the limb is unloaded. In navicular horses, however, DDFT tension and navicular bone pressure are significantly higher in the early part of the stance.

"It appears that horses with navicular syndrome will attempt to compensate for the condition by unloading the heels via contraction of the DDF muscle," Wilson said. "This process, however, increases the force in the DDFT and hence the compressive force exerted on the navicular bone. This may result in a positive feedback loop (with increased pressure on the bone causing increased bone remodeling), accounting for the chronic nature of the condition. A similar reaction to other heel pain would also lead to increased loading of the navicular bone."

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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