Could it be a allergy

[Waterway65]

I have a mare that that nearly always has breathing problems starting late July until November. At first I tried to blame it on feed but I watch it really close with her and no other horses have this problem. When she is real bad she has had cortisone shots. The rest of the year she is fine with no issues. Opinions would be appreciate.

 

[Bigfoot]

Yes, I have seen horses have issues with allergies. Actually a horse with allergies, is how I got started spraying pastures. Weeds went away, and the problem went away. yours may not be that simple.