As maturity increases, the protein level decreases. Grass hay should be cut when it first starts to head. Typical grass hay will run from 8 to 12 percent protein. Cutting alfalfa early will also increase palatability. Young, tender plants have a higher leaf to stem ratio, and more food value is in the leaves than in the stems.
Color is a very good indicator of quality.
Sun bleaching, rain damage, and age are all indicated by light colored hay. Bleached hay usually indicates lower protein, lower energy, and lower vitamin and mineral levels, as well as decreased palatability. The moisture level in hay is critical. You need enough moisture for good leaf retention, but not enough to cause mold or spoilage. Hay baled at 15 to 18 percent moisture should be fine.