| Popis: |
Summary Thirty-six male Holstein calves, 89±9 days of age and partially depleted of their vitamin A stores to an average of 8.9±4.0 γ per 100ml. of plasma, were fed one of three initial carotene intakes, 100, 300, or 900 γ per lb. live weight per day, for a 6-wk. period, and thereafter, one of four final carotene intakes, 20, 60, 180, or 540 γ , for a 12-wk. period. Both plasma carotenoids and vitamin A concentrations were found to respond to current carotene intake, with the more rapid changes observed when the carotene intake was changed from a high to a low intake, as compared with a low or a medium to a high. The initial vitamin A status, as indicated by plasma concentrations at the termination of the initial carotene intake period, influenced the response of plasma and liver vitamin A concentration observed for the final 12-wk. carotene intake period, in that greater carotene intakes were required to obtain a desired response in the case of the lower initial plasma vitamin A concentrations. Based on calculated tocopherol intakes, artificially dehydrated alfalfa resulted in increased plasma and liver concentrations of this vitamin. |
