well you can try several things... there are different thrush applications with different Ph levels.
Also keep her out of the mud or wet bedding for a while. If possible, turn out in a dry place would be best to avoid the mud and bacteria getting back in there, if it's really bad.
Some people dont have luck with thrush buster, others do. Make sure before you do anything that you clean the area with a stiff brush to get the dirt out and expose the area, and even go as far as scrubbing it with a betadine soap or something to get it good and clean. Make sure you dry the foot before you apply anything to it. Keep her standing in cross ties for a few minutes to make sure it is dry, bc otherwise you just trap moisture in there which is exactly what thrush needs to grow.
Ive heard that making a sugardine solution works well... Mix Betadine (or a generic form) with white table sugar into a paste and apply it to the areas.
You can also try ointments from the pharmacy that are made to treat Athlete's Foot. Thrush is a yeast infection, as is Athlete's foot. You can also try monistat or anything made for a typical human yeast infection as well.
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