EFFECT OF SUPPLEMENTAL DIETARY VITAMIN-E AND ZINC ON REPRODUCTIVE-PERFORMANCE OF DAIRY-COWS AND HEIFERS FED EXCESS IRON

We tested the hypothesis that the incidence of retained fetal membrane s could be reduced by limiting oxidative stress. Sixty-four primigravi d heifers (56 Holstein and 8 Jersey) and 80 multiparous cows (64 Holst ein and 16 Jersey) were used. A combination of vitamin E or Zn and Fe was fed in a 2 x 2 x 2 factorial arrangement during the last 42 d prep artum. Amounts of supplements per animal were 1000 IU of vitamin E (d, l alpha-tocopheryl acetate), 0.8 g of Zn (Zn-Met and ZnSO4), and 12 g of Fe (FeSO4. 7H(2)O) for Holsteins and 9 g for Jerseys. Neither vitam in E nor Zn directly affected the incidence of retained fetal membrane s, but plasma alpha-tocopherol was lower when fetal membranes were ret ained >12 h or when vitamin E was not supplemented. Iron had no direct negative effects on reproductive performance, but cows receiving addi tional Fe had lower unsaturated iron-binding capacity, which, in turn, was also lower in cows that retained fetal membranes. Days to first o bserved estrus were reduced by supplementation with either vitamin E o r Zn. Vitamin E reduced days to first artificial insemination (AI) and tended to reduce days open. Supplemental Zn tended to reduce days to first Al but did not affect days open. Milk production during the firs t 12 wk and AI per conception were not affected by supplementation wit h either vitamin E or Zn. Both vitamin E and Zn reduced days to first observed estrus, indicating improved reproductive health during the ea rly postpartum period.