Contracted heels in horses can lead to lameness and many people believe this is caused by metal shoes. Heel contraction in horses involves narrowing of the caudal (toward the tail) part of the hoof including the frog, buttress, and heel bulbs. To determine if a heel is contracted, you can measure the width of the heel 2 ½ inches from the buttress and compare that distance to the width 1 inch from the toe. If the width of the heel is the smaller of the two measurements, the heel is contracted. Another method is to measure the length of the frog and compare that to the width of the frog. If the width is less than 67% or 1/3 of the length of the frog, the heel is contracted.
Although metal shoes are blamed for causing heel contraction, there is no scientific evidence to support this. A study was performed in Poland on 114 horses from 22 different premises. Results showed that the use of metal horseshoes was not related to heel contraction but that heel contraction is a multifactorial problem with many different related causes. In many cases, heel contraction is related to the breed involved as well as poor trimming and shoeing techniques. Only about 8% of feral horses have contracted heels but up to 100% of the domestic horses in one study had contracted heels. However, it made no difference if the horses that had contracted heels were shod or not. Some believe that horseshoes restrict the movement of the heels and lead to contraction, but this does not appear to be the case. One previous study did find that horseshoes could have an effect on contraction but these horses were running on a hard surface versus working on a grass pasture. So, if your horse needs shoes, it is unlikely the use of shoes will lead to contracted heels as long as the horse has access to soft ground and is trimmed properly.