My miniature horse just recently started coughing when I was exercising her. She has never done this before. She is 7 years old and is healthy otherwise. No nasal discharge or fever. No loss in appetite and is still very energetic. Last spring, she coughed several times while out in the pasture and I was told it was allergies and eventually she just worked herself out of it. But this year, she has begun coughing while being worked and I don't hear her cough while she is standing around. After she coughs, her mouth has a white foam and it appears to be a dry cough. Please let me know what you think!!