Thrush is a common bacterial infection of the horny parts of the sole. Usually the frog is infected but the sole and/or white line can be involved. Though easy to diagnose and usually easy to treat, when environmental conditions and hoof conformation predispose to the problem it can be a chronic recurring problem. This article discusses diagnosis, treatment, and prevention.

Thrush is a common bacterial infection of the horn of the horses hoof. Thrush can infect the frog, sole, or white line. The organism that causes thrush is a anerobic bacteria, Fusobacterium necrophorum, though other organisms have been implicated. These organisms secrete keratinolytic enzymes that break down the horn of the hoof. However these organisms need a wet dirty environment to prosper since oxygen destroys them. Besides a wet environment the condition of the frog and sole can aid in the establishment of thrush.

Contracted heels results in the sulcus or central groove of the frog closing up and deepening. This provides for an ideal location to trap dirt and moisture so thrush prospers and is a common complication of this type conformation. Deep closed collateral grooves of the frog, often a result of poor trimming, can also predispose to thrush. Other conditions that lead to thrush are defects in the harder portions of the sole that trap moisture and dirt. Chronically foundered horses with seedy toe usually will have focal spots of thrush in the seedy toe. Flaps in the frog or cracks in the sole can trap moisture and dirt setting up a focal area of thrush.

Since thrush infects the horn where there are no nerves it is not painful in the early stages. However if the area of thrush is allowed to persist it will dissolve the underlying horn and the infection deepening until it reaches sensitive tissue where infection sets up and becomes very painful. If it is a large patch of thrush the infection sits on the surface exposing more sensitive tissue. Focal areas in the sole or white line turn into subsolar abscesses.