Neuroaxonal dystrophy (NAD) is a degenerative central nervous system disease of horses, humans, and other animals. Horses affected with NAD usually appear dull or depressed with weakness and mild to severe gait abnormalities (ataxia) that affect all four limbs, although the hind limbs are usually more severely affected. Clinical signs of NAD are usually first observed in young horses under the age of two. Neuroaxonal dystrophy is believed to be a heritable trait.

Neuroaxonal dystrophy is similar to equine degenerative myelopathy (EDM). Both diseases cause degenerative changes in the central nervous system. Differences between NAD and EDM depend on what specific areas of the central nervous system are affected. Vitamin E deficiency is associated with both NAD and EDM. Horses affected with NAD on one farm in California had variable serum vitamin E concentrations, and nutritional analysis showed that vitamin E concentrations in grass on that farm were low. Vitamin E supplementation and selective breeding reduced, but did not eliminate, NAD cases in following years. Research is in progress to develop a genetic test for NAD, so horses with the gene will hopefully not be bred or transmit the disease to their offspring.

Other diseases to rule out in young horses with gait abnormalities before diagnosing them with NAD include cervical vertebral malformation (wobblers), equine protozoal myeloencephalitis (EPM), EDM, and central nervous system or spinal trauma. Diagnostic testing can include neurologic examination, radiographs (X rays) of the neck vertebrae, spinal tap, and measurement of vitamin E in the blood and diet. Several equine neurologic diseases, such as NAD, EDM, and equine motor neuron disease (EMND), have been shown to be caused by vitamin E deficiency or to improve following vitamin E supplementation. Many veterinarians will include vitamin E therapy in their treatment of equine neurologic disease for its neuroprotective effects and for its role in preventing or reducing the clinical signs of degenerative nervous system disorders.

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