Causes
Thrush is caused by bacteria that are trapped in usually the deepest part of the hoof (sulci). The bacteria breed best in an anaerobic environment. Wet conditions are not enough for this to occur though, unsanitary conditions along with wet conditions are ideal for the bacteria.
Signs and Symptoms
There are two very distinct signs that are most noted if thrush is present. The First is the unmistakable order that will come from the foot. The other is the black discharge around the frog and infected sights. Normally you will also see deep cracks at the central sulcus of the frog. Many times thrush does not cause lameness but left untreated thrush can make its way to more sensitive areas causing pain and lameness.
Treatment and Prevention
There are many commercial products available to treat thrush. The first thing I would recommend is to find out how the material is being trapped to allow the bacteria to grow. If the frog has flaps have your farrier cut them away. Debridement is always the best first step if possible. If a deep central sulcus crack is seen, I like to soak cotton balls with whatever your choice of thrush remedy is and stuff it down into the crack. As the crack heals it will push the cotton out. I will list and give my thoughts on several of my favorite commercial products below this section. Lastly clean the foot and clean the foot often. Remove the horse from any moist environments as much as possible while you are fighting thrush.
Some of my Favorite Thrush Treatment Products
No Thrush - http://www.nothrushshop.com
Today - http://www.tractorsupply.com/today-10cc-12-pack-fort-dodge-animal-health-2205355
Thrush Buster - http://www.smartpakequine.com/thrush-buster-210p.aspx
Hoofflex Thrush Remedy - http://www.absorbine.com/products/hoof-care/hooflex-thrush-remedy
Banixx - http://www.banixx.com/