Horse thrush is a bacterial infection induced by excessive muck and stuff in the frog of the horse's foot. Thrush has a very distinct smell and the horse is probably going to have a painful middle region of its foot and maybe 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 spare cash to shell out on keeping their horse thrush-free so it's probably great to know that there are methods 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 not ideal, some people even apply bleach or hydrogen peroxide. It is however important that care is be taken so as not to do more harm than good by employing 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 looking lame then you should consider calling on a vet. You should not leave it for too long because 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. Proper foot care with a hook knife and perhaps a miniature wire brush to clean out the cracks in the animal's feet is important to make sure that your horse does not get thrush.
From a practical point of view, keeping the animal out of soft and muddy areas for prolonged periods is important as is making sure that the stable is kept clean. You should ensure that your horse doesn't collect a build-up of muck in it's feet. That's your best chance of towards maintaining your horse thrush-free.