Careful stable and hoof management is essential to prevent thrush. Because the bacteria are killed by oxygen, regular use of the hoof pick will allow air to the foot and reduce the ability of the bacteria to take hold.
The prime cause, however, is one of hygiene — standing in droppings and urine. The damp conditions of a dirty stable provide the perfect environment for this anaerobic bacteria, (those needing a low-oxygen environment) which cause thrush to flourish.
If a horse has thrush the underlying cause needs to be identified and removed. The horse should be moved to a clean, dry environment and the feet cleaned daily.
Thrush will never resolve unless the hoof hygiene is good.