UltraCuz Equine Selenium Yeast is a supplement that contains organically chelated selenium, a key mineral needed for breeding performance, energy demand and healthy metabolic function. Selenium is an important antioxidant in Horses that provides the Horse with necessary Muscle and joint support. Selenium is important for maintaining a healthy immune system and helps protect the body's tissues from free radical damage. Performance Horses have a high energy demand, and their Muscle cells require a large amount of antioxidants, including selenium. Selenium is essential for breeding mares, as inadequate selenium can have a negative effect on colostrum quality as well as both mare and foal plasma and Muscle.