Analysis in horse hair as a means of evaluating selenium toxicoses and long-term exposures

Authors: Davis, Thomas - Zane; Stegelmeier, Bryan; HALL, JEFFERY - Utah Veterinary Diagnostics Laboratory

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2014
Publication Date: 7/30/2014
Publication URL: http://handle.nal.usda.gov/10113/4791522
Citation: Davis, T.Z., Stegelmeier, B.L., Hall, J.O. 2014. Analysis in horse hair as a means of evaluating selenium toxicoses and long-term exposures. Journal of Agricultural and Food Chemistry. 62(30):7393-7397.

Interpretive Summary: Selenium is important for many enzymes in horses however, too much of this trace mineral can be toxic. In fact few other minerals needed by horses have such a narrow margin of safety. Horses can suffer from chronic selenosis if too much Se is ingested in the diet over periods of weeks or months. Clinical signs of poisoning in affected horses may include dysplastic or corrugated hoof lesions, dull hair coat, mane and tail alopecia, and varying lameness with severe cases resulting in untreatable hoof necrosis and sloughing resulting in euthanasia. In an actual field case in which three horses were suspected of chronic selenium poisoning, the mane and tail samples were segmented and analyzed for selenium content by inductively coupled plasma mass spectrometry to identify the approximate time of exposure and to confirm the initial diagnosis. The selenium concentrations in the hair reflected a pattern that corresponded to the rotational grazing schedule between the contaminated and non-contaminated pastures for the previous three years and confirmed the diagnosis of chronic selenosis. The results of this study demonstrate that sampling and segmenting of equine tail and mane can be a valuable tool to document or determine exposure to excessive Se in the diet for up to three years post-exposure in some cases. Additionally, this study demonstrates that the concentrations of Se in mane and tail hair remain relatively stable over time.

Technical Abstract: Horses are susceptible to chronic selenosis if grazed on seleniferous forages for a prolonged period. In this study, mane and tail samples from horses that exhibited classical hoof lesions of chronic selenosis were analyzed by inductively coupled plasma mass spectrometry for selenium (Se) content. The horses had grazed for 6 months, from approximately May 15 until November 15, each year for three grazing seasons in a pasture containing seleniferous forages and water sources with elecated Se concentrations. The segmented hair sampled showed cyclic pattern in Se concentrations in the mane and tail, which corresponded to entering and exiting the contaminated pasture. The Se concentration in the tail of one horse could be traced for three grazing seasons. These reults demonstrate that in some cases hair samples can be used to determine Se exposure in horses for up to 3 years postexposure.