My horse is 20-23 years old. He has Heaves. He was prescribed dexamethasone-sp for management. The vet who gave it to us will not answer us so I can get another bottle. Horse is currently pulling in at the ribs and just miserable. What is a good supplement to help his airway? Smart breathe, cough free? I only have a tractor supply and normal feed stores avaliable in town along with online of course.