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By Bob Agne, DVM

Thrush is a common hoof problem that many horse owners and care givers recognize.  Although most mild cases of thrush do not cause lameness, it can become more serious and cause pain, lameness and/or more severe infection if left untreated.  Additionally, the presence of thrush may be an indication of more serious foot problems.

Thrush is observed as a black, foul smelling discharge from the central or lateral sulci or grooves of the frog.  It can affect either hind or front feet.  Typically the affected sulcus is deeper than normal and the horse may exhibit pain when these areas are cleaned.  Discharge from the affected area is variable and may not be noticed unless the sulcus is closely examined and cleaned out.  In more advanced cases the frog and sole tissue can become undermined with the exposure of sensitive corium and swelling of the lower limb.  Often horses with contracted heels and atrophied or weak and narrow frogs are more susceptible due to the depth of the sulci and similarly, horses with overgrown hooves are more prone to the problem.

Thrush is caused by a bacterial infection of the insensitive tissue of the frog which can then, if left untreated infected deeper skin layers.  Although no specific organism has been isolated as the cause of thrush, and in most cases a number of bacteria can be cultured from the affected area, Fusobacterium necrophorum is a common isolate.  Because of the bacterial nature of the infection, horses that live in a wet mucky environment are more susceptible to infection.

Prevention, obviously, is preferable to treatment and regular cleaning, inspection and trimming/shoeing is important.  Additionally, providing clean, dry bedding for horses confined to a stall is imperative.  Exercise helps to maintain healthy blood flow to all regions of the foot and helps to maintain a healthy frog with normal hoof architecture.

Treatment of early, mild cases involves debridement or removal of affected tissue and treatment with a topical astringent.  Several commercial products are available or tincture of iodine or a ‘sugardine’ (equal parts of betadine and white sugar) can be applied.  Treatment should be continued until infection is controlled and the horse should be kept in a clean dry environment.  More serious case, that require the attention of a veterinarian, may involve more extensive debridement, antibiotic therapy and therapeutic shoeing that protect the affected area while providing access to the lesion

Often, thrush will occur in horses that are well maintained with otherwise normal, healthy feet, however in some cases the presence of thrush may be an indication of an underlying problem in either the management of the horse or the health of the foot.  Certainly when a mild case of thrush does not respond to initial therapy a veterinarian should be consulted, the horse’s environment and hoof care should be reviewed and, in the case of horses with contracted heels and narrow, atrophied frogs a thorough foot exam should be performed as this conformation is consistent with chronic heel pain in the horse.
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