Thrush is an infection often progressing to necrosis of the frog, which can lead to shrinking of the frog. The affected feet of horses will have black, malodorous discharge, usually in the sulci (grooves on either side of the frog). Contributing factors are wet, unhygienic environments and deep sulci that harbor bacteria. Treatment involves debriding diseased tissues, keeping the feet clean, and changing the horse’s environment to a dry, clean stall or dry yard. Topical application of astringent (such as thrush buster, iodine, or mastitis medications) with or without foot bandages may be repeated until the infection is controlled.