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 various influencing factors on the retinol plasma level and the vitamin-A-depot of liver. Liver vitamin-A-depot of calves depends on carotene or vitamin-A-intake of cows and vitamin-A-concentration of milk, respectively. Two to three weeks old calves born during the summer contained more liver-vitamin-A (>100 IU g⁻¹) than animals born during the winter season. Feeding of first colostrum improves vitamin A supply of calves because of the decrease of vitamin A in milk with following milkings (1st milking: 100%, 2nd: 74%, 3rd: 41%). Besides the vitamin-A-depot of liver of calves carotene content of feeds and vitamin-A-supply influenced the vitamin-A-status of growing cattle. About 25000 IU vitamin A per 100 kg body weight per day were necessary to keep the liver vitamin A depot on a constant level (≈ 100 IU g⁻¹). The results show a homeostasis of retinol in plasma of calves. The concentration of retinol in plasma was regulated very exactly, if the liver stores of calves were higher than 25 IU g⁻¹. Therefore, the plasma level indicates the status of vitamin A storage only if there is an extreme depletion of vitamin A. At marginal depletion, however, there is damage to peripheral tissue 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 judging the necessity of a vitamin A substitution.

Key words:

• Vitamin A
• calf
• liver
• plasma