Vitamin E in the Nutrition of Cattle II. Vitamin E Levels in the Blood, Vitamin a and Carotene Utilization, and Other Chemical Studies

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Abstract
Estimations have been made of the total fat-soluble reducing substances, calculated as α-tocopherol, in the blood plasma of dairy cattle fed rations in which the amount of vitamin E was below that measurable by rat bioassay. Two animals, one which died 20 days later and one with cardiac abnormalities, had calculated tocopherol levels of less than 100 µg %. Similar measurements for a later group of three unsupplemented animals over a 14-month period gave an average value of 249 µg %, considerably lower than the value of 685 µg % found for a corresponding group of animals supplemented with mixed tocopherols, and also lower than values reported in the literature for animals fed normal rations. Measurements of the blood plasma carotene and vitamin A levels of three supplemented and three unsupplemented animals on controlled carotene and vitamin A intakes showed that the feeding of the low vitamin E ration did not impair the utilization of carotene and vitamin A. Some studies on possible procedures for the removal of interference in the chemical assay for tocopherols by the Emmerie-Engel procedure are reported. These include an alternate procedure for the removal of carotene interference based on the oxidative destruction of the carotene under conditions where α-tocopherol is quantitatively converted to α-tocopherylquinone. The quinone is then converted by reductive cyclization to α-tocopherol and measured as such.
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