Road founder comes from the concussion on the feet, build
up of blood and heat in the feet but it's not a metabolic problem which
grass founder is. Grass founder causes inflammation of the laminae but
from a different cause than road founder. Grass founder is usually more
severe. A horse can "road founder" and never have a problem
again. If the horse was on grass everyday and he was used to it, I
would not suspect founder unless there were something in the grass that might
have been toxic, if it was a new growth of grass or if it had recently undergone
a hard frost. Was there heat in the feet? Were X-rays taken?
How did the horse act? Did he just go down? Could it have been
something else? West Nile Virus perhaps? And no, road founder does
not predispose the horse to foundering on grass.