Do you the source of the crack? Does it come from a dry hoof? In this case, our colorless and hydrating ointment PURE PROTEC will allow you to deeply feed the hoof and soften it to avoid the crack extension. The application of this product regularly is a good way to prevent that kind of problem.
However, if the crack is too large and extend, it will be necessary to call you farrier. He will be able to proceed different ways depending on the foot condition.