ROLE OF VITAMIN E AND ZINC IN CELLULAR ADAPTATION, OXIDATIVE STRESS AND METABOLIC STRESS IN DAIRY ANIMALS: A REVIEW

Periparturient cows undergo instance mammary growth, copious synthesis and secretion of carbohydrate, fat and proteins as well as marked accumulation of colostrum and milk. Since colostrum is rich in vitamins A and E, therefore, cows require increased supply of these vitamins prior to parturition. At parturition, due to increased colostrogenesis, there is diversion of zinc from plasma pool towards mammary gland. Decrease in serum zinc level at calving is also associated with an acute phase response due to inflammatory reaction in uterus. Stress at calving induces synthesis of zincdistribution protein metallothionein and zinc is redistributed from blood pool to other tissues such as liver. During periparturient period when there is significant decrease in vitamin E level andzinc, the cow’s immunity status and neutrophil functions are depressed.Supplementation of vitamin E maintains proper antioxidant status of animals and improves the ability to resist infections.Zinc is an integral part of immune system.It has been indicated that zinc had an indispensable role in the development and maintenance of immunocompetence. Zinc is also known to be associated with superoxide dismutase (SOD) which is an important antioxidant enzyme involved in oxidative stress. Also role of vitamin E and zinc in energy metabolism like increase blood glucose level and decreaseNEFA during early lactation when animals are under negative energy balance.