Hay is a plant; it's a natural product and it can be sensitive to light and ventilation conditions. Our hay is hand-packed, so we know that when it leaves our facility, it is lovely and fresh. We even pack in boxes, not plastic, so the hay can breathe properly and all that yumminess is protected from light.
During transport, however, weather, humidity, and other factors can cause some issues. Frustrating, we know. When feeding your hay, give it a good sniff. It should smell fresh, green, and earthy. Fluff it in your hands... there should be no grey-ish black dusty residue on the leaves or stalks.
Here is healthy hay:
Here is moldy hay: