It is well documented that the functions of vitamin E and selenium (Se) are related and that animal responses to supplementation of either nutrient can depend on the nutritional status of the other nutrient Supplementing 740 IU vitamin E/day throughout the dry period reduced incidence of clinical mastitis by 37% and duration of mammary infections by 44% in cows fed a diet low in Se (Smith et al., 1984). Control cows in this study had a 41% incidence of clinical mastitis and a 0.41 month duration of infection per quarter lactating. reported that supplementing 4000 IU of vitamin E/day for 14 days prepartum reduced new intramammary gland infections and incidence of clinical mastitis in early lactation by 63% and 89%, respectively, compared to control cows fed 100 IU/day. Incidence of clinical mastitis in cows fed 100 IU of vitamin E/day in this study was approximately 27%. Supplementation of cows in this study with 1000 IU of vitamin E/day was less effective (30% vs. 89% reduction) in preventing mastitis than 4000 IU/day. In this study all cows were supplemented with 0.1 mg Se/kg diet, a level that would be considered low or marginal relative to requirements. In contrast, found that supplementation with 1000 IU of vitamin E/day did not affect incidence of clinical mastitis in dairy cows fed diets low in Se (0.10–0.12 mg Se/kg in the diet). Differences in Se status may explain the discrepancy in response to vitamin E between these studies . Plasma Se concentrations in cows were much lower in the study. Incidence of retained placenta also has been reduced by oral or intramuscular (IM) administra-
tion of vitamin E but responses have been variable . found that I