[gamingirl22]

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!!

 

[Exotic]

Could be dust from the arena. I've noticed horses to cough more in cold weather too. Maybe from the crisp air and moving around along with the dust.
If she is having foam I would have the vet take a look. At least you would whether it was anything or not and be able to solve the issue.
Or maybe she isn't chewing her food good and is choking. Need teeth looked at?
Vet could help in that area as well.