1-3 mg of Se per day is the recommended daily intake for horses. 5 mg of Se per day ventures into possible toxicity, but the jury is out on the exact OD level. Over 50 mg/day is definitely bad and possibly lethal, but unless your horse gets into the supplements, this level of ingestion is unlikely. 

...............CherryHorse Blog..................
Last Edited By: AppyButt Apr 12 10 5:26 PM. Edited 1 times.