Effects of antioxidant supplementation during the periparturient period on the antioxidant status, reproductive performance, and milk production of dairy cows

In addition to the stress of calving and initiation of lactation, a dairy cow may also be susceptible to oxidative stress. Oxidative stress occurs when prooxidants exceed antioxidants. Reactive oxygen metabolites are a natural part of metabolism; however, under periods of trauma or stress, the release of free iron can exacerbate their formation causing the production of more reactive free radicals. During the critical time of parturition, supplementation with additional antioxidant nutrients may improve the antioxidant status of the cow and also have both direct and indirect effects on reproduction and milk production in the subsequent lactation. In order to test this hypothesis, 126 dairy cows were fed diets supplemented with either vitamin E or trace elements (TE)[4-Plex ®, Zinpro Corporation , Eden Prairie, MN] as well as excess dietary iron. Excess iron, a prooxidant, decreased measurements of most plasma antioxidants. Supplementation with vitamin E and TE increased antioxidant levels depending on the class of antioxidant measured. Vitamin E increased radical scavenging and chain breaking antioxidants; whereas, TE increased iron binding and iron oxidizing antioxidants. There was no effect on the presence of retained fetal membrane (RFM) by any combination of supplement when all cows were considered. However, RFM was negatively correlated to iron binding and iron oxidizing antioxidants which were in turn increased by TE supplementation. Reproductive performance was impaired in cows that suffered from RFM: having later onset of luteal activity, normal luteal activity, first observed estrus, and more days open. When only those cows with RFM were considered, TE did remove some of the harmful effects. Increased supplementation with antioxidant nutrients appears to improve overall antioxidant status and may also improve reproductive performance particularly when the dairy cow is under stress such as RPM.