EPM is a serious neurological disease of horses caused by the protozoan Sarcocystis neurona, requiring prompt diagnosis and treatment to prevent permanent neurological damage.
EPM causes significant welfare harm through neurological pain, disorientation, and loss of motor control that prevents normal movement and behavior. Severely affected horses cannot eat, drink, or move normally and experience significant distress. The insidious onset means mild cases are often missed until significant spinal cord damage has occurred. Prompt treatment substantially improves prognosis and reduces welfare harm. Preventing opossum access to hay, feed, and water sources is the most effective prevention strategy in endemic areas. Horses with permanent severe neurological deficits that cannot be managed may require humane euthanasia to end suffering.