You should check it carefully for weeds..... (Dr. Kellon)I recently read about a horse belonging to natural horsemanship trainer/clinician, Dan James having similar symptoms. (stocking up - laminitis) This horse also had symptoms of tying-up. He ingested the weed *hoary alyssum* in hay they obtained in Michigan while on tour. The article said horses usually will not eat it in the pasture, but do not find it as offensive in hay and will sometimes eat it. They had several horses eating the same hay. They watched all of them carefully for several days, but discovered only one horse must have actually eaten the weed and got sick.
All I know about this is from the article I read. I don't know if the weed is even found in your area. Still, I thought I should throw it out there...just in case. From what I read, it is a nasty little weed if eaten!
Teri, Stormy and Kelsey