The other day I had a client ask me "what would you use for a horse that has a cough?"
It really depends on If the cough just started or if it's been lingering for a little while. In most cases homeopathy is what I usually use. For a cough that has just started, I will try Aconite (which is also used for SHOCK). But if it has been a little while, then I use Belladonna, (may seem anxious and delirious), and Alluim Cepa (raw onion) if they have profuse tearing of the eyes. I may also use Nux Vomica (for symptoms brought on by cold and dry weather) as long as the horse does NOT have high fever or the symptoms worsen when eating.
Histamine or Alluim Cepa are both good for allergies. For horses that have become chronic, you would actually start off with a smaller dose, like 6c or 30c. But for horses that may just be coming down with the symptoms a higher dose, like 200c is usually more effective.
All of these natural remedies can be purchased at any health food store and often are available through a chiropractor.
"Everybody's Guide to Homeopathic Medicines" by Stephen Cummings, MD and Dana Ullman, PHD, pages 68-69.