Equine protozoal myeloencephalitis (EPM) is a serious neurological disease caused by protozoal parasites, causing progressive neurological signs and significant welfare compromise in affected horses.
EPM causes progressive neurological damage that impairs a horse ability to move normally, maintain balance, and engage in social behaviors. The condition can progress to severe ataxia where horses are at risk of falling and injuring themselves. Pain from muscle atrophy and the distress of neurological dysfunction both contribute to welfare compromise. Early diagnosis and prompt treatment improves welfare outcomes significantly, as delayed treatment allows more neurological damage to accumulate. Return to prior athletic function is not guaranteed, raising difficult decisions about horses that cannot safely return to work. The welfare considerations extend to decisions about ongoing care, workload modification, and when progressive neurological compromise warrants humane euthanasia.