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.

In their study, Bailly and his fellow researchers analyzed 21 isolates of fungus found on moldy hay and straw, carrying out identification on both a morphological (microscopic-shape-based) and molecular (DNA-based) level. They also measured each strain’s toxicity using mass spectrometry.

They identified nine strains of Stachybotrys chartarum and 11 strains of S. chlorohalonata (plus one strain that requires further analysis for identification). Each analyzed strain had its own different levels of components and composition, which is why horses display clinical signs of varying severity based on which strain they consume.

However, eight of the nine S. chartarum strains were shown to be “highly toxic,” Bailly