My 15 yo mare developed a strange cough about a year and a half ago. She's been treated for pneumonia, asthma, and other things.. She's even had an ultrasound on her lungs and nothing... The vet said we could do further testing but she basically said that some horses just develope a cough for no reason or it could be allergies. Is there anything I can do to sooth her cough when it's acting up? I just started her on an allergy pouder to see if that will help but she's still coughing and with the weather changing it gets to be really bad some days. Does anybody have any advise on what to try?