Regular commenter and friend of Terra Sig, leigh (the path forward), let us know overnight that Florida State Veterinarian Dr Thomas J Holt officially confirmed that selenium overdose killed 21 Venezuelian polo horses in Wellington, Florida, on 19 April.
An attempt by an Ocala, Florida, compounding pharmacy to reproduce an equine dietary supplement called Biodyl resulted in a toxic dose of sodium selenite to be given to the horses. The pharmacy is cooperating fully with the FDA and other authorities but there is no official word as to whether the pharmacy made a calculation error or were given an improper formula by the requesting veterinarian.
We predicted that of the components of Biodyl, sodium selenite was the most likely culprit. It is required in microgram doses and even a 100-fold calculation error could have led to toxicity. A superb comment thread developed at our post with several members of the equine community weighing in as well as a discussion on the practice of compounding pharmacy.
For my money, the best news outlet coverage of the toxicology report comes from Andy Reid and Missy Diaz at the South Florida Sun-Sentinel. This report has the most details on the investigation and is the only one I could find this morning that indicates the magnitude of the selenium toxicity:
Toxicology results of the horses showed the animals had as much as 15 times the amount of selenium in their blood and as much as 20 times in their liver as normal, said veterinarian Dr. John Harvey, the executive associate dean of the University of Florida’s college of veterinary medicine.