Not necessarily mold causing the problem. As JimR stated, I too have 'hay fever' and grew up on the farm never being able to get a good breath of air in my lungs. Hay dust was bad, but straw dust and oats was really bad.
Now I stay out of hay and usually don't have problems breathing. But just get near a bag of niger seed for the birds, and my lungs just 'plug' up and I can't get a breath.
I think some of it is phsycological too, as I could go to a movie and see people rolling in the hay or threshing oats or wheat, and immediately get plugged and swollen lungs.
Its not a pleasant feeling, but one which certainly kept me far away from cigarette smoke. Respirators helped a little bit, but the smell and odor of hay and oats will shut my lungs down, and that smell isn't stopped by a mask or repirator.
You may want to make some decisions about working in hay, and they may not be ones you choose to do willingly. /forums/images/graemlins/frown.gif