feed hay mold
Most of the time, the mold that forms on the outside of bales is due to humidity issues, which can be difficult to control in our climate. Some barns and storage facilities are more conducive to mold generation than others. Consider ways to increase air flow or improve ventilation to reduce humidity inside the storage area, if possible.
You could consider composting the moldy hay or using it for mulch. Bedding for poultry may be another option. Information on types of mold and options for utilizing the hay is available on this fact sheet: http://www.extension.uidaho.edu/forage/Fact%20Sheets/Moldy%20hay%20in%20Idaho.pdf