Vitamin E+SE XL™ contains twice the level of selenium and nearly twice the level of vitamin E contained in standard selenium and vitamin E supplements. Vitamin E and Selenium are important antioxidants that work together to support a healthy immune system. While vitamin E is found naturally in fresh grass, levels begin to drop the moment grass is cut for hay. In addition, many soils are deficient in selenium, making it hard to reach the recommended daily requirement of this mineral without supplementation. Determine total selenium content in ration prior to supplementation. Powder form.