Horse Guard was the first to manufacture an over-the-counter selenium supplement for horses in 1978. Founder, Del Johnson, recognized the need for low selenium horses to be supplemented. Horse Guard creates the best selenium supplement for horses. The organic form of selenium is what your horse would consume naturally if the forage had enough selenium. Most companies use the inorganic form of selenium because it is costs less. However, research shows when fed organic selenium horses are able to absorb it better than those fed inorganic selenium.
The amount of selenium in a supplement is also very important. Research has shown horses supplemented with 3 mg of selenium had increased immune function and greater reproductive efficiency than horses fed 1 mg of selenium. So, when considering a selenium supplement for horses only buy a product that contains 3 mg of 100% organic selenium.