RESUMEN
Free radicals (FRs), also known as reactive oxygen species (ROS), are usually established in the body when adequate oxygen depletion occurs. Oxidative stress and the establishment of FRs in the body are mainly caused by high metabolic activity, the need for rapid growth, inadequate flock management, exposure to viral and bacterial microorganisms, and adverse environmental conditions. Furthermore, FRs can also be produced during the activity of phagocytes when they depend on the action of ROS to kill the engulfed pathogen. FRs have very adverse effects on all cells, particularly the cells of the immune system. They are extremely erratic and reactive molecules that directly harm DNA, cellular proteins, lipids, and carbohydrates within cells. Antioxidants are substances that can eliminate and neutralize FRs within the body and free the body from the oxidative stress that occurs due to the accumulation of FRs. Many vitamins and minerals support the activity and effect of the immune system in fighting against microbes and cancer, which mostly depend on their antioxidant elements to diminish the negative impact of FRs in the body. Examples are vitamin C, vitamin E, superoxide dismutase, selenium, glycine, cofactors of glutathione peroxidase, manganese, essential oils, and phenolic compounds.