According to a news story originally posted by British magazine Horse and Hound, the deaths of 40 horses–which occurred between March and June–residing on five different farms in Queensland, Australia, remain under investigation. Australian veterinarians have told reporters that they suspect the culprit is a tropical plant of, or related to, the species Crotalaria.

Crotalaria spp are in the same family as the pea. The plants are sometimes referred to as rattlepods because their seeds become loose inside the pods and rattle when the pods are shaken. While some plants in the pea family clearly can be ingested safely, others, like Crotalaria, are highly toxic and horses are particularly susceptible to the poison.

"Some species of Crotalaria and other plants contain toxins called pyrrolizidine alkaloids, which are naturally occuring compounds that are toxic to the liver," advised Thomas Tobin, MVB, MSc, PhD, MRCVS, Dipl. ABT, a specialist in equine pharmacology, therapeutics and toxicology in theDepartment of Veterinary Science at the University of Kentucky's Gluck Equine Research Center.

He added, "This toxin, which is most concentrated in the flowers of the plant, causes liver degeneration and liver failure after chronic (long-term) grazing by horses