The currently recommended intake of vitamin E for dairy cows is based on the prevention of nutritional myopathy, a calf disease. However, it is likely that the vitamin E requirement of the modern dairy cow is very different from that of a calf. This review of the literature investigates the effect of vitamin E supplementation on the health and fertility of the dairy cow. Supplementation of high levels of vitamin E (at least 1000 iu per day) during the dry period and early lactation can reduce the incidence of mastitis, possibly because of an increase in immune system activity and function, but there appears to be little benefit of supplementation on infectious diseases other than mastitis. The evidence for a response in the reproductive system is more equivocal. In herds with a history of selenium deficiency and a high incidence of retained fetal membranes, supplementation, in conjunction with selenium, can reduce retention, but the evidence for an effect of supplementation on other reproductive diseases, such as cystic ovarian disease and metritis, is based on a very limited number of cases. The literature suggests that the current recommendations for vitamin E are inadequate. In particular, it suggests that the current linking of requirement to dry matter intake is incorrect, because vitamin E requirement is probably at its highest when intake is at its lowest. However, the majority of the data on which this conclusion is based, come from North America where cows will encounter significantly different levels of oxidative stress from cows in the EU.
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