Solving the Laminitis Puzzle

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Kentucky Derby winner Barbaro’s gallant struggle with and eventual demise from laminitis brought renewed, worldwide attention to the disease. Those who deal with horses regularly are already all too familiar with it, but it seems that veterinarians and researchers are even more determined to figure out all the pieces to the laminitis puzzle. In the coming years, more studies will hopefully improve methods of diagnosis, treatment and eventually prevention of this deadly disease.

As we know, laminitis occurs when the laminae, the sensitive tissue beneath the hoof wall, separates from the bone, and there is decreased blood supply to the foot. When there is nothing left to support the bone, rotation of the third phalanx (P3 or coffin bone) can occur due to the pull from the deep digital flexor tendon attached to the back of the bone. Sinking of the bone, where the entire bone drops down, can also happen. In severe cases, it will drop the entire way through the sole of the foot. Of those horses affected, 75 percent will ultimately develop severe or chronic lameness, and it is still the second most deadly disease in horses (behind colic).

Pasture Associated Laminitis

This June, thousands of veterinarians will gather in Seattle, Washington, for the 2007 ACVIM Forum. New ways to prevent and manage laminitis will be one of the main areas of discussion. Ray Geor, director of research at the MARE Center in Virginia, will speak on risk factors with a focus on the overweight horse and pasture-associated laminitis. Approximately half of the horses that develop laminitis are on pasture when the disease develops. The sugar content of the grass is believed to be the trigger, and insulin resistance makes some horses more susceptible.

Dr. Barry Fitzgerald at the University of Kentucky’s Maxwell H. Gluck Equine Research Center has written about an in vitro study where removing glucose from the culture medium leads to rapid separation of the hoof lamella tissue when subjected to stress forces. Something similar may occur in insulin resistant horses, because insulin isn’t able to induce glucose uptake into the cell. Impaired glucose uptake combined with inflammation and obesity and/or post-operative conditions may weaken the lamellae. Therapeutic drugs that increase insulin sensitivity and decrease inflammation may work together to treat this type of laminitis effectively.

Diagnostic?Methods

Laminitis is difficult to manage because of challenges in predicting the disease’s course. In the 1990s, Ric Redden, DVM, farrier and founder of the International Equine Podiatry Center in Versailles, KY, and Dr. Chriss Pollitt of Queensland, Australia, worked together to develop the venogram, which has become an extremely helpful tool in evaluating the laminitic foot. The venogram works by injecting contrast media into the digital vein. Then a tourniquet goes over the fetlock and radiographs are taken. Since it has been established that the laminitic foot has decreased blood supply, a venogram can show the decline even before coffin bone rotation is detected in an x-ray—and catching it at that point can mean all the difference. Even though traditionally, veterinarians have diagnosed laminitis via rotation, it is now considered that once rotation happens, the horse is already in big trouble.

Along these same lines, researchers at the University of Georgia have isolated the arteries and veins of the hoof. The blood vessel dysfunction is thought to be in the veins, but to confirm it, they examined the differences between contraction properties of the arteries and veins. They found that laminitic veins had a lower contractile response and the wall tightness in the veins is higher in the laminitic foot. Once they completely understand the mechanisms, they can begin to develop treatment options.

Upcoming?Studies

There is even more research on the horizon. The Grayson-Jockey Club Foundation is distributing over

$1 million for research grants in 2007. Thirteen new projects have been approved, and three of those focus on laminitis. They are:

Factors that trigger the onset of acute laminitis, University of Georgia. The goal here is to understand the basic factors that lead to acute laminitis. When specific white blood cells leave the circulation and enter soft tissues in the laminae, inflammation occurs and acute laminitis can be the result. Figuring out what triggers this response would help determine the origins of laminitis.

Early treatment of acute laminitis with lidocaine, Ohio State University and University of Massachusetts. This study will examine treating early laminitis cases with intravenous lidocaine (a local anesthetic), which researchers believe will decrease the changes leading to laminar failure. If lidocaine does block some of the early mechanisms, it will become a viable treatment option.

Levothyroxine as a treatment for insulin resistance in horses (toward a defense against laminitis), University of Tennessee and University of Pennsylvania. The drug levothyroxine is a synthetic form of thyroxine (thyroid hormone) that is used to treat hypothyroidism in humans. It can be safely given to horses to induce weight loss and increase insulin sensitivity. It is helpful when given to horses with Equine Metabolic Syndrome, a combination of insulin resistance, obesity and laminitis. Further studying LT4 will hopefully establish the drug as an effective treatment for insulin resistance in horses, which will make them less likely to develop laminitis.

There is obviously still much to learn about laminitis, but there are many in the scientific community putting forth tremendous effort to do just that. The answers will come, and perhaps one day we will have solid prevention tactics and positive, cost-effective treatment options that will halt laminitis in its tracks.