Influence of Various Vitamin-A-supplies on its Concentration in Liver and Plasma of Calves

Abstract

Five individual feeding experiments with male calves were conducted to investigate variou influencing factors on t h retirzol plasma level and the vitamin-A-depot of liver Liver vitamin-A-depot of calves depends on carotene or vitamin-A-intake of cows an,d vitamin,-A-concentration of milk, respectively. ?Eoo to three weeks old calves born during the summer contained more liver-vitamin-A (>lo0 IU g-') than animals born during the winter season. Feeding of first colostrurn improves vitamin A supply of calves because of the decrease of vitamin A in milk with following milkings (1st milking: loo%, 2nd : 74%, 3rd : 41%). Besides the vitamin-A-depot of liver of calves carotene content of feeds and vitamin-A-supply influ.enced the vitamin-A-status of growing cattle. About 25000 IU vitamin A per 100 kg body weight per day wefe necessary to keep the liver vitamin A depot on a constant level (= 100 IU g-). The results show a homeostasis of retinol in plasma of calves. The concentration of retinol in plasma was regulated very exactly, i f the liver stores of calves were higher than 25 IU g-'. Therefore, the plasma level in,dicates the status of vitamin A storage only i f there is an extreme depletion of vitamin A. At marginal depletion, howevel; there is damage to peripheral tissu.e before changes in the vitamin-A-level in serum occur The determination of vitamin A in serum or plasma gives no information on the adequacy of liver reserves for ju&ng the necessity of a vitamin A su,bstitution.