Cassie keeps her feed shed clean. She is protecting her horse from equine protozoal myeloencephalitis, or EPM. EPM is a disease spread by opossums. This disease affects the nervous system. Horses contract EPM by sniffing an affected opossum's excretement. EPM is rather serious. Virginia has a high opossum population. If the area you live in has any opossums make sure you don't leave any spilled grain lying around and that you keep the lid on the grain bin tight! Spilled or otherwise available grain is high on the opossum gourmet list, so spilled grain in a opossum infested area is a invitation for EPM.