Question: We suspect we have hoary alyssum in our hay. We’ve noticed our horses are stocked-up, but we are not sure if its from hoary alyssum or because all of the snow is limiting their ability to walk around. Can you confirm if this is hoary alyssym in our hay?

Answer: Yes, hoary alyssum is in this hay.

One seed head is circled in red and more can be seen throughout the photo.

Hoary Alyssum can be identified by small, oval seed pods that become translucent as they mature showing the small brown to black colored seeds inside the pods.

We recommend you immediately stop feeding the hoary alyssum-infested hay. Hoary alyssum only affects horses, so the hay can be fed to cattle, sheep and goats.

Horses can react differently to hoary alyssum, but signs of toxicity are usually seen 12 to 24 hours after a horse ingests the plant.

Common signs include swelling and fluid build-up in the lower legs (e.g. “stocking-up”), a fever of 103F or higher, stiff joints, and an unwillingness to move. More severe cases can progress to laminitis.

Mild stocking up is most common; however, more severe signs can occur in horses eating hay with more hoary alyssum or when ingesting the hoary alyssum-infested hay for longer periods of time.

Clinical signs normally go away with supportive treatment 2 to 4 days after removing the infested hay. Horses with laminitis may take more time to recover.

For more information on hoary alyssum toxicity, click here.

Written by Krishona Martinson, PhD, University of Minnesota. This and other horse nutrition articles can be found at http://www.extension.umn.edu/agriculture/horse/nutrition/.