Thrush is an infection of the frog of the hoof and of the grooves (sulci) on either side of the frog causing a thick, black, smelly discharge. Once thought to be caused by a wet and dirty environment, experts now believe certain factors contribute to the development of thrush even in the cleanest situations. The horse's hoof design and movement in action provide a natural cleaning mechanism. However, abnormal hoof shape, improper trimming, insufficient exercise, chronic lameness, poor diet and poor circulation can all disrupt the natural cleaning mechanism and allow infection to set in.
The infected hoof should be picked, cleaned and medicated as recommended by the veterinarian or farrier. There are several products available to help treat Thrush, however; unless the underlying cause of the Thrush is diagnosed and corrected, it will return. The hoof should be balanced as much as possible, the horse should be turned out as well as worked, and any causes of chronic lameness should be treated.
There are several bacteria and fungi thought to be involved in Thrush, including Fusobacterium necrophorum. If these organisms invade deep enough and infect living tissue, the horse may become lame from the condition. In a serious case like this, the veterinarian and farrier may need to work together to perform more extensive cleaning that involves removing dead and infected tissue before healing can begin. In this situation, it is even more important that the primary reason for Thrush be identified and treated.