Most feed tags include a statement cautioning against offering moldy feed or hay to horses.
Owners might suspect mold when they see white, blue, or greenish powdery substances in hay or feed; black spots on hay; or simply by detecting a musty smell in damp, heavy hay. It is crucial to notice mold and avoid feeding molded feedstuffs because the fungus itself—or organisms it produces—have the potential to cause illness and even death in horses.