• Equine motor neuron disease (EMND) is caused by the degeneration of the motor neurons, which control the movement of the large muscles. “This affects the motor neurons and therefore the skeletal muscles,” says Paul Siciliano, PhD, of North Carolina State University. “In a horse with this problem, you’ll see great appetite—eating very well—but these horses waste away, losing muscle mass, and may die without intervention.

“I observed this problem firsthand in a group of blood donor horses maintained at a veterinary hospital,” Siciliano adds. “They were fed the leftover hay from the prior year. It was good hay, not moldy, but it had been stored a long time. Over time, the hay gradually loses the compound that has vitamin E activity. The horses became vitamin deficient and eventually developed motor neuron disease.”

[To read more about why horses need vitamin E click here.]

EMND does not develop quickly. “When studies tried to replicate this in an experimental setting—to make horses deficient—it took nearly two years of feeding a low vitamin E diet before any signs occurred,” says Siciliano. “When people see a problem, they immediately wonder what they’ve done to cause this change, but the reality is that the problem occurred because they didn’t change anything—the horse stayed on a deficient diet for a long period of time.”

• Equine degenerative myeloencephalopathy (EDM) is caused by damage to the nerves in the spinal cord and parts of the brain. It typically develops in younger horses, those who are less than 2 years old, and it causes ataxia (incoordination) and loss of proprioception (the sense of where their body and limbs are located).

EDM seems to run in families, which suggests that the cause is genetic. However, the disease is also characterized by low levels of vitamin E, and supplementing with this nutrient helps horses improve. While low levels of vitamin E do not appear to be a direct cause of EDM, it’s possible that a vitamin deficiency could produce the signs in a horse who is also genetically predisposed to the disease.

[Is your horse getting enough vitamin E? Click here to find out.]

• White muscle disease, a degeneration of the skeletal muscles, is caused by a deficiency of selenium, another potent antioxidant. But low levels of vitamin E also seem to play a role in the disease. “Selenium and vitamin E are both important for muscle function and work as antioxidants, but with slightly different jobs,” Siciliano says. Higher levels of one nutrient can help compensate for lower levels of the other, and signs of deficiency are more likely to occur in horses with low levels of both.

• Sporadic exertional rhabdomyolysis (“tying up”) is a severe, painful cramping of the large muscles that can occur during or just after exercise. “Exertional rhabdomyolysis has many causes, but one thought is that it can be caused by inadequate levels of vitamin E,” says Carey Williams, PhD, an equine extension specialist with Rutgers, the State University of New Jersey. “During research trials in my lab, we had a few horses that were marginal in terms of plasma vitamin E levels. They had more of a tendency to tie up during or after the exercise, or at least be very muscle sore with higher levels of creatine kinase [a muscle enzyme that is abnormally high in the blood when horses tie up]. Many people who have horses who suffer from tying up problems are feeding 5,000 IU of vitamin E, and that does seem to help.”

Don’t miss out! With the free weekly EQUUS newsletter, you’ll get the latest horse health information delivered right to your in basket! If you’re not already receiving the EQUUS newsletter, click here to sign up. It’s *free*!