When a calf is stressed, hormones trigger many changes in blood chemistry and metabolism. It may stop eating, using its own body tissues to generate energy. Immune functions may be sharply curtailed. There is ample evidence that preventive action, including good vitamin nutrition, can head off stress-related ailments. Vitamin E and selenium are both tissue antioxidants.
Vitamin E works in cell membrane fractions.
Selenium has its effect in the cystosol fraction. Thus, the functions of selenium and vitamin E are independent and additive. One of the main physiological changes brought by stress is elevation of serum glucocorticoid levels, which has been shown to reduce lymphocyte and antibody production and functions. Also, greater epinephrine secretions lead to higher levels of prostaglandin, lipoxin and other fat-based immunosuppressant enzymes. Stress also leads to the release of arachidonic acid from the membrane phospholipids.