A neighbor advised you that if a possum poops in horse feed the horse will contract some kind of disease and die True?

Answer 1

It is possible. The disease your neighbor is talking about is equine protozoal myeloencephalitis (EPM). Currently it is generally accepted that EPM is caused by aberrant migration of a parasite (Sarcocystis neurona) through the central nervous system of a horse. S. neurona is commonly found in raccoons, where it is an intestinal parasite that is transmitted through the feces.

Treatment for EPM is generally symptomatic and not particularly helpful; the damage is caused by the parasite and there isn't much a veterinarian or anyone else can do to reverse the damage to the neurons. Most horses diagnosed with EPM are either retired to pasture or breeding (if the damage is mild) or are euthanized for humane reasons.

However, there are plenty of horses exposed to raccoon feces in their feed who never get EPM, and there are some horses who develop EPM but have no history of exposure to raccoons.