EQUUS - - EQ Medical Front -

as far back as six such cy­cles---or three years. Hair from the healthy horse, who had only re­cently been moved to the pas­ture, did not show a sim­i­lar pat­tern.

“The tail hair from one of the mares was 36 inches long,” says Zane Davis, PhD. “The tail hair on the other horses was about 24 inches long. Tail hair on horses grows at an av­er­age rate of 0.9 inches per month while mane hair grows at about 0.7 to 0.8 inches per month. Con­se­quently, you can de­ter­mine the tim­ing of a toxic ex­po­sure at some pre­vi­ous time de­pen­dent upon the length of the hair sam­ples.”

The sit­u­a­tion that led to tox­i­co­sis in th­ese horses is un­com­mon, says Davis. “In the area where th­ese horses were poi­soned, land man­agers typ­i­cally know which ar­eas are a risk and use them cau­tiously by grazing less sus­cep­ti­ble species for shorter pe­ri­ods of time. How­ever, in states such as Wy­oming and the Dako­tas, for­ages from ar­eas with high se­le­nium are some­times har­vested and sold. Horses then in­gest high lev­els of se­le­nium with­out the own­ers know­ing.”

Nonethe­less, Davis says, this case has sig­nif­i­cant im­pli­ca­tions for other horses. “We were able to doc­u­ment ex­po­sure three years [later]. In ad­di­tion, the study showed that the se­le­nium con­cen­tra­tions are sta­ble in the hair.” This may help di­ag­nose cases of se­le­nium tox­i­co­sis even years after the ex­po­sure oc­curs. Ref­er­ence: “Anal­y­sis in horse hair as a means of eval­u­at­ing se­le­nium tox­i­coses and long-term ex­po­sures,” Jour­nal of Agri­cul­tural and Food Chem­istry, July 2014

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