OXIDATIVE STRESS, ANTIOXIDANTS, AND ANIMAL FUNCTION

Reactive oxygen metabolites generated during normal metabolism and met abolism stimulated by xenobiotics can enter into reactions that, when uncontrolled, can impair performance of dairy cows. Direct effects inc lude peroxidative changes in membranes and other cellular components. Indirectly, competitive consumption of reducing equivalents can interf ere with important metabolic functions and divert glucose from other p athways by inducing the monophosphate shunt. Normally, the body is pro tected by a wide range of antioxidant systems working in concert. Meta l catalysts of oxidative reactions are removed in extracellular fluids by metal-binding macromolecules. Superoxide dismutases, glutathione p eroxidase, and catalase within cells remove superoxide and peroxides b efore they react with metal catalysts to form more reactive species. F inally, peroxidative chain reactions initiated by reactive species tha t escaped enzymatic degradation are terminated by chain-breaking antio xidants, including water-soluble ascorbate, glutathione, and urate and lipid-soluble vitamin E, ubiquinone, and beta-carotene. To optimize p erformance, oxidative stress in high producing cows must be controlled by supplying all known antioxidant nutrients and by minimizing effect s of substances that stimulate reactive oxygen metabolites.