(New York) Selenium deficiency in equids: EDTA whole blood and serum samples from a 12-year-old Palomino horse and EDTA whole blood from two 15-year-old miniature donkeys with generalized weakness were submitted to the AHDC. The horse and donkeys were located on separate premises.

The horse had a subacute presentation of weakness. On exam, this horse was reluctant to turn, had difficulty rising, and had generalized muscle fasciculations. The donkeys had a 2-year history of progressive weakness and lameness. Both owners had concerns about hay quality. Selenium was undetected in the whole blood from all three animals. Our assay detects Selenium above 2.5 ug/dL (equine reference interval 14.0-24.0 ug/dL). Selenium below the detectable amount is considered a profound deficiency in an adult animal. Serum vitamin E concentration in the horse was 345 ug/dL (equine reference interval 200-1,000 ug/dL). Vitamin E was not measured in the donkeys. 

At the AHDC, selenium is measured in EDTA whole blood (purple top tube). A separate serum sample, kept chilled and protected from light is necessary for vitamin E analysis. Vitamin E plays a cooperative antioxidant role with selenium, and should be measured concurrently whenever possible. A deficiency in either vitamin E or selenium does not always coincide with a deficiency in the other, and disease can be present despite only having a deficiency in one. Equine motor neuron disease is a sequelae of vitamin E/selenium deficiency and muscle atrophy and weakness are the main clinical signs.