Effects of Evaporative Cooling Prepartum and Vitamin E Supplementation on Performance of Holstein Cows During Summer

摘要

Background. A specific requirement by periparturient cows for vitamin E has not been defined yet because titration studies are lacking. The recommended rate of supplemental vitamin E is 0.73 and 0.36 IU/pound of body weight for nonlactating, pregnantcows and lactating cows, respectively (NRC, 2001). A 1450 lb cow supplemented at the recommended vitamin E guideline would consume daily -1000 IU prepartum and ~ 500 IU postpartum of supplemental vitamin E. Cows fed fresh green forages will likely require less supplemental vitamin E. Life changes that increase metabolic demands, such as parturition and copious production of milk, increase oxygen requirements substantially. As a result, the production of reactive oxygen species (ROS) such as O_2, OH", H_2O_2, and lipid peroxy radical (LOO) increases. Oxidative stress results when ROS are produced faster than they can be neutralized by antioxidants (Sies, 1991). Oxidative stress usually occurs during the periparturient period (Ronchi et al., 2000) and may contribute to periparturient disorders (Brezezinska-Slebodzinska et al., 1994) and be associated with metabolic diseases (Ronchi et al., 2000). The predominant antioxidant in biological membranes is a-tocopherol. Thermal stress may aggravate oxidativestress (Bernanucci et al., 2002). Feeding additional vitamin E as an antioxidant in the summer during the periparturient period may be needed due to the greater oxidative stress caused by elevated temperature and humidity.