Response: Crown rust is a fungus that affects the leaves of oat, and spreads from leaf to leaf via spores. There are some varieties of oat that are more resistant to crown rust than others.
Crown rust on oat should not pose a major health risk to your horses once baled. However, crown rust will likely decrease the nutrient value of the hay (decreased protein and digestible energy levels) and may decrease the palatability (the horses willingness to ingest the hay) of the hay. Therefore, it is recommended that you test the hay for forage quality and supplement with a vitamin/mineral mix or concentrate as needed.
More importantly, crown rust may make the hay dusty, which could lead to respiratory issues. Feeding the hay outdoors and pulling apart the flakes prior to feeding may help to decrease the dust level. Wetting (not soaking) the hay with water prior to feeding will also help reduce the chance the horse will inhale the dust and spore particles.
Author: Krishona Martinson, PhD, University of Minnesota