MIAMI, April 28 -- The 21 polo horses that mysteriously collapsed and died last week likely perished from an overdose of selenium in an incorrectly mixed vitamin supplement, according to information released by Florida state investigators and the Ocala, Fla.-based pharmacy that produced the supplement.
http://www.washingtonpost.com/wp-dyn/content/article/2009/04/28/AR2009042803482.html?hpid=sec-sport