Thrush is an anaerobic bacterial infection that thrives (without oxygen) in the the deep crevices of horse's feet, usually within the groves adjacent to the frog and the central groove of the frog, called the central sulcus.

Thrush infection usually results in a strong, repulsive smell and black greasy or pasty discharge. The bacteria causing thrush break down frog and hoof tissue, causing progressive deepening of the grooves of the frog. In severe cases, thrush can result in lameness and a deformed, worn-away frog and very deep grooves. In rare cases, the infection can dissect all the way through the frog and into the underlying important structures of the hoof.

Thrush develops especially in horses in which mud or manure remains packed on the sole over time, creating an anaerobic environment where these organisms can thrive. Although thrush commonly occurs in horses that are stalled in wet dirty environments, it can occur in any horse or any environment. But it is more common in stabled horses than those that are at pasture.

Thrush can also develop secondary to another problem that causes lameness and poor use of the hoof. If a horse does not bear full weight on a foot, the underlying tissues are not given the opportunity to expand and contract (which helps keep the sole clean), and thrush may develop as a result.

In general, horses that stand around a stable, without adequate exercise, have a higher incidence of thrush. Horse's hooves function best when the horse exercises regularly.

DIAGNOSIS- Any horse with abnormally deep grooves of the frog usually has some degree of thrush. If there is a black, smelly discharge in these grooves, that is thrush.

Treatment depends on the severity of the condition. The most important aspect of treating thrush involves removal of excess (dead or under-run) frog and hoof tissue to allow air penetration deeper into the frog grooves. This should always be coupled with management to increase exercise, which improves hoof health and function and tends to keep them cleaned out.

Topical antiseptics of many kinds will kill thrush bacteria, but they are useless alone. Without trimming excess tissue away, the topical simply does not get down to the area where the bacteria are thriving and eating away the hoof tissue.

In severe cases, particularly when blood or pus is present or where lameness results, veterinary assessment and treatment is needed. In all cases, underlying causes must be ruled out.

Thrush may be misdiagnosed as canker, which is a completely different and comparatively more severe condition that is treated differently. Whereas thrush is a necrotic process in which the tissues deteriorates and dies, canker is the abnormal production of keratin that occurs in live tissue resulting in tissue growth. If your horse has been diagnosed with thrush but the treatment is not effective, your horse may have canker.