Beware of moldy hay. According to French researchers, it can contain certain strains of mycotoxins that can poison your horse—and yourself.

French researchers have identified, for the first time, specific strains of Stachybotrys fungi in moldy fodder, bringing to light a serious source of toxicity in horses that can cause a variety of symptoms, from mild to fatal.

But that’s not all. That same fungus can also lead to health problems in handlers, said Jean-Denis Bailly, DVM, professor in the National Veterinary School of Toulouse. He presented his group’s work at the 42nd French Equine Research Day, held March 17 in Paris.

Horses are particularly sensitive to Stachybotrys fungi, Bailly said. Clinical signs range from a simple drop in performance levels (lack of willingness to work, refusing jumps, etc.) to sudden death with no warning signs