Horse thrush is an infection caused by excessive muck and stuff in the frog of the horse's foot. Thrush has a strong odor and the horse is probably going to have a painful middle region of its foot and possibly also the wider areas of the foot. Cracks in the tissue with darkened areas are an usualy indication of horse thrush.
Lots people don't have much cash to shell out on keeping their horse thrush-free so it's probably great to be aware that there are ways and means to look after your horse on a tight budget if thrush strikes. Antiseptics can assist and a lot of people use Betadine, Kopertox or Thrush Buster. Although a very rough and far from ideal, some people even apply bleach or hydrogen peroxide. Obviously though it is important that great care is be taken so as not to do more harm than good by using the wrong thing.
It's perfectly possible to look after your animal yourself if the situation is noticed in time. However, if your animal appears to be showing signs of lameness then you should consider calling on a vet. Do not leave it for too long otherwise it will cause major damage to the foot of the horse.
Daily cleaning of the frogs of the horse's feet is a recommended prevention against thrush. Good foot care with a hook knife and perhaps a miniature wire brush to clean out the cracks in the horse's foot is important to make sure that your animal does not become a victim of thrush.
From a practical point of view, keeping the animal out of soft and muddy areas for prolonged periods is important as is ensuring that the stable is kept clean. You should make sure that your horse does not accumulate a build-up of muck in it's feet. That's your best chance of towards maintaining your horse thrush-free.