When supplements kill: selenium overdose kills 21 horses

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SUMMARY

The tragic deaths of 21 polo horses were caused by a selenium overdose due to a compounding pharmacy's error, where 5 mg/mL of selenium was mistakenly added instead of the intended 0.5 mg/mL. This significant dosage error highlights the extreme sensitivity of horses to selenium, an essential mineral that can be toxic in high amounts. For context, a typical human supplement like "Centrum Silver" contains only 55 µg (0.055 mg) of selenium, indicating that the equine dosage was equivalent to approximately 100 tablets. This incident underscores the critical need for accurate dosing in equine nutrition.

PREREQUISITES
  • Understanding of equine nutrition and dietary requirements
  • Knowledge of selenium's role and toxicity in animal health
  • Familiarity with compounding pharmacy practices and regulations
  • Awareness of the differences in mineral tolerance between species
NEXT STEPS
  • Research the safe dosage levels of selenium for horses
  • Learn about the effects of mineral toxicity in equines
  • Investigate best practices for compounding medications for animals
  • Explore case studies on equine health incidents related to dietary errors
USEFUL FOR

Veterinarians, equine nutritionists, horse owners, and anyone involved in the care and management of horses will benefit from reading this discussion.

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Conclusion to the polo story. A compounding pharmacy mixed up vitamins and electrolytes for sports horses, but they added 5 mg/mL selenium instead of 0.5 mg/mL, which was the lethal mistake. (It does not say what the total dose was).

Selenium Overdose Caused Deaths of Polo Horses
http://scienceblogs.com/grrlscientist/2009/04/selenium_overdose_caused_death.php

For comparison (I looked up), "Centrum Silver" has 55ug Se (0.055 mg), so 5 mg is about 100 tables - most of a bottle.

http://www.centrum.com/product_detail.aspx?productid=CENTRUMSLVR&panel=tablets
 
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Horses are VERY sensitive to selenium. They need a little bit as an essential mineral, but can easily overdose. The safety margin isn't so bad with humans. I know of one horse farm that had well water and had to get city water brought in for watering the horses, because the well water had too high of a concentration of selenium. It was still safe for people to drink, but too high for the horses.