(NY) Marked selenium deficiency was diagnosed in a 27 year old Arabian mare. The horse was found in lateral recumbency, unable to move into sternal without assistance. She had been apparently normal the day before. Muscle fasciculations were present over the neck. The horse was current on vaccinations for Rabies, Eastern Equine Encephalitis (EEE), Western Equine Encephalitis, Tetanus, and West Nile Virus (WNV). Serum and EDTA whole blood were collected prior to euthanasia.

Ancillary testing for Equine Herpesvirus-1 and EEE were negative. Antibody testing for WNV was consistent with previous vaccination. The vitamin E concentration was at the low end of the reference range and the selenium concentration was markedly low at 2.72 ug/dL (reference range 14-24 ug/dL). Although the brain was not submitted to definitively rule out rabies and other etiologies for this clinical presentation, we are presuming that the selenium deficiency was a significant factor in this case. As we head further into Arbovirus season in the northeast, this example highlights the importance of keeping non-infectious causes of neurologic illness on your differential list as well.