Stepping Ahead: Bluegrass Laminitis Symposium 2001
Laminitis is one of the most serious and difficult-to-treat diseases horses can get, and only by learning everything about this problem can we prevent and treat it successfully. Enter the 14th annual Bluegrass Laminitis Symposium held Jan. 25-27 in Louisville, Ky. This symposium has long been a mecca for farriers, researchers, and hoof-specialty veterinarians, who sat in rapt attention while listening to cutting-edge presentations on hoof microanatomy, biomechanics, navicular disease, wild vs. domestic horse hooves, properly documenting hoof treatment, photographic and radiographic techniques, possible mechanisms of laminitis, pain management, measurement of blood flow, and laminitis and navicular treatment. They also were treated to live shoeing demonstrations.
Ric Redden, DVM, symposium host and owner of the International Equine Podiatry Center in Versailles, Ky., began the symposium by discussing the differences between domestic horse hooves and the hooves of wild horses he has worked with near Las Vegas, Nev. While the wild horses' hooves were quite variable in terms of moisture, growth, and bone alignment, the differences between them and domestic horse hooves--and the lower rates of several problems very common to domestic horses--have many people rethinking their concept of a horse's ideal foot. "Researchers today need to find a way to standardize the model," Redden emphasized, "or we have no common ground to talk about."
Redden also discussed a new shoe he developed based on his experiences with the four-point trim and significantly lame horses. His new shoe, currently used only by him and called the "banana shoe" by many at his farm, moves breakover much farther back than normal and leaves an "air space" below the heels. This effectively allows the horse to load whatever region of the foot that is the most comfortable for him. "This also opens the angle of the tendon going over the navicular bone, and decreases the mechanical load on the bone," Redden said. "It unloads the tendon significantly."
David Hood, DVM, PhD, of the Texas A&M Department of Veterinary Physiology and Pharmacology, discussed factors in making an accurate prognosis for recovery from laminitis. These include pathology (anatomic and physiological deviations from the normal state), pain, infection, treatment(s) applied, client sensitivity, goals of rehabilitation, and economics.
"Prognosis must be based on a combination of factors," Hood said. "There currently is no formula for accurate prognosis."
Hood also discussed the importance and management of pain in diagnosing and treating hoof problems. While it can be hard on the owner, "Pain is a protective mechanism, so it should not always be treated," said Hood. "Pain level is also a common result of rehabilitation process, so it is not always an indicator of therapeutic success. We should avoid excesses in treatment."
Laminitis Update From Australia
The first presentation by Chris Pollitt, BVSc, PhD, of the Australian Equine Laminitis Research Unit at the University of Queensland, was on the microanatomy of the hoof. He said, "Unless we understand the normal anatomy of the hoof, we will never understand the pathology."
After familiarizing the audience with hoof anatomy on the cellular level, Pollitt updated them on his latest research findings regarding the mechanisms of laminitis. Based on these findings, Pollitt hypothesizes that the considerable increase in the Streptococcus bacteria content in the gut that is seen with carbohydrate overload breaks down the gut wall to some extent, allowing toxins and bacterial metalloproteinases (enzymes) to get into the bloodstream.
Once in the bloodstream, these substances quickly reach the hooves, where they degrade the attachment of the secondary laminae to the basement membrane that attaches the outer, insensitive structures of the hoof to the inner ones. With degradation of the tiny secondary laminae comes degradation of the capillaries bringing blood to them, forcing blood through shunts to the primary laminae instead and dilating those vessels (vasodilating). This delivers more of the damaging laminitis trigger factors present in the bloodstream to the primary laminae. "Arteriovenous shunting now appears to be a result of pathological changes, not the cause," Pollitt said.
Support for this proposed mechanism includes the fact that virginiamycin anti-biotic administered before carbohydrate overload prevented laminitis by limiting the bacterial population. Administering it at the same time as carbohydrate overload did not limit the bacteria enough to prevent laminitis.
Another factor supporting this hypothesis is that in hoof samples treated with metalloproteinase enzymes, specific enzyme inhib-itors controlled the hoof wall separation to some degree.
Studies are underway to evaluate the efficacy of cold therapy in constricting blood vessels and thus minimizing the delivery of laminitis trigger factors to the hoof. This could help prevent laminitis in at-risk horses (such as ones that just raided the feed room).
More Laminitis Research
Steve Adair, MS, DVM, Dipl. ACVS, of the University of Tenn-essee, presented his studies of laminar microvascular blood flow measured by laser Doppler flowmetry. "The principle of this method (of measurement) is to measure the Doppler shift, i.e., the frequency change that light undergoes when reflected by moving objects such as red blood cells," Adair said. "It is a non-invasive, continuous method of measuring microvascular blood flow. I think it's very important to use information like this for model standardization so we can compare apples to apples."
In laminitis induced with black walnut extract, laminar microvascular blood flow decreases in the early stages, followed by reperfusion (restoration of blood flow). After reperfusion, blood flow decreases again and symptoms begin to appear. Adair suggests that to avoid laminar damage, treatment should begin prior to the onset of clinical signs. Treatment after clinical signs appear might keep them from getting worse.
Alan Wilson of the Royal Veterinary College has conducted studies on the biomechanics of navicular horses, and by combining force plate data with careful measurement of the hoof and mathematical equations, calculated force exerted on the navicular bone by the deep digital flexor tendon. He found that force on the navicular bone in horses classified as having navicular problems was nearly double that of sound horses in the early phase of the stride.
"This was due to a higher force in the deep digital flexor tendon, which was attributed to a contraction of the deep digital flexor muscle in early stance in an attempt to unload the heels," Wilson said.
This theory also explains why another of his studies found a decrease in force on the navicular bone of affected horses after analgesia (numbing) of the nerves that area. With less pain, they did not try to keep pressure off the heels.
Preventive Foot Care
Richard A. Mansmann, VMD, PhD, of the Central Carolina Equine Practice, discussed his findings from the first 50 horses he put on a preventive foot care program in his practice. His preventive foot care program involves baseline measurements of the horse's feet--both external and on radiographs--and an assessment of the horse's conformation, diet, exercise, movement, and overall condition.
"The primary goal is to enhance the foot awareness of the farrier, veterinarian, and owner," Mansmann said. "Secondly, each member can then respond to any changes that occur, with the ultimate goal of prolonging soundness. Recording the data is really important--you know if there's a change; you're not just guessing."
As reported in our AAEP Wrap-Up in February, 66% of these 50 horses had some health problem of which the owner and farrier were previously unaware (see "How-To Sessions, Timely Topics"). Mismatched feet were a problem with 54% of the horses, while 38% were overweight and/or had a cresty neck. The third most common unidentified problem was a lack of heel support, affecting 36% of the horses, while hind leg suspensory pain was a problem for 20%. Sore backs were a problem for 10% of the horses, thin soles affected 8% of the horses, ringbone arthritis affected 6%, and coffin bone rotation was seen in 4%.
"I wonder how many of the laminitis cases we see had a previous problem we weren't aware of," Mansmann concluded.
Live Shoeing Demonstrations
Following three days of seminars, Redden conducted live shoeing demonstrations in the conference hotel, with a video crew transmitting the proceedings to the big screen in the seminar room across the hall. Attendees enjoyed watching shoeing of some difficult cases by Redden, farrier Bernard Duvernay, and American Farrier's Association Certified Farrier Bernard Pelletier, with constant commentary from all three. Every case had X rays done before and after the shoeing, focusing on bone alignment and getting the maximum amount of information about the case before starting to trim the hoof.
The most spectacular case was a neglected mare with an old case of laminitis and superficial flexor tendon contracture in one foreleg. She got a superficial flexor tenotomy in addition to a trim, and a heel-elevation shoe was applied to that foot.
This seminar provided new ammunition for the fight against laminitis and navicular disease. Vets and farriers are hopeful that we soon will win the war against these debilitating problems.
About the Author
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.
POLL: University Equine Hospitals