Hoary alyssum is toxic when the fresh plant is grazed in the pasture and/or the dried plant is consumed in hay. In most cases, mild "stocking up" has been observed in horses on pasture or in those ingesting hay with less than 20% hoary alyssum. However, more severe clinical signs have been observed in horses ingesting hay with more than 20% hoary alyssum.
Yes, Hoary alyssum can be found in Livingston county.
Identification - one to three feet tall, white flowers with four deeply divided petals. Seeds pods are oblong with a point on the end. Please see attached pictures for reference.
If indeed the plant is identified as Hoary alyssum in your hay fields it should not be fed to horses and would be advisable to find an alternative market for the hay.