Signs of spoiled hay under cover include a musty or moldy odor, which indicates the presence of moisture and mold growth. Discoloration, such as black or gray spots, can also signal spoilage.
The texture of the hay may become excessively damp or clumped, making it feel slimy or mushy. Additionally, the presence of visible mold or mildew on the surface of the hay is a clear sign of degradation.