How do vets know what's wrong with animals? I mean the animals can't tell them where it hurts. By appearance I guess but appearances can be deceiving. Thank you for your reply MaCC! :)
Don't know if a horse can become "hoarse" but many do suffer from a chronic respiratory malady called "the heaves". It's believed to be caused by an allergic reaction to "dust" that they've breathed in at some point, but that's just a theory. It's a rough analog to COPD in humans.
It's basically incurable but the effects can be somewhat relieved by the administration of the steroid prednisolone (prednisone has been shown to be ineffective). A number of "herbal" remedies are also reported to be effective. Even smearing mentholated petroleum jelly (VIcks Vaporub) in the nostrils can provide relief.
B.H.Wilson 