I ran across this old article recently in the May 1999 issue of Anvil Magazine. It is a writeup from the Bluegrass Laminitis Symposium from the same year. It summarizes the talks that were presented, one of which was by Dr. Christopher Johnston, DVM, PhD, on the study of the effect of shoes on hoof expansion:
Christopher Johnston, DVM, PhD, spoke about Impact in the Athletic Horse; about Heel Expansion; and also about Objective Biomechanical Testing of Horseshoes. Dr. Johnston finds that a softer surface may absorb as much as 90% of the impact forces. In his laboratory studies, as much as 80% of the impact force on the limb is absorbed in the hoof, before it reaches P2.
Dr. Johnston outlined three possible explanations for heel expansion of the hoof under load: the frog pressure theory, the depression theory, and the hemodynamic theory. Every one of these may play a part. Using a thin wire attached to the heels and a potentiometer, Dr. Johnston found about 1 mm (1/24 of an inch) expansion at the heels under load, followed by contraction of the heels as the hoof approached breakover during motion. Shoes decreased the amount of expansion and contraction.
I found this short blurb interesting in that it states matter of factly that shoes prevented expansion of the hoof. There’s no way to tell what if any discussion was generated at the symposium, but this study is over ten years old and it appears to have died a quiet death. I think this is a far more significant finding than there is credit being given, as most farriers and authors will dispute that shoes prevent hoof expansion.
I have not been able to find anything on the original study by Dr. Johnston. If anyone is familiar with where to locate it, please post.
Link to article: