[Factors influencing the vitamin A concentration in the liver of cattle]

Nineteen long-term individual- and group-feeding experiments with 180 male calves, 338 growing bulls, 302 heifers, and 344 dairy cows were carried out in order to measure the influence of feeding (straw, silages or green fodder as roughages) and different vitamin-A supplies (0-40,000 IU per 100 kg body weight per day in growing cattle or 0-120,000 IU per dairy cow per day) on liver vitamin-A concentration. All together, 2,127 biopsies from livers were taken for retinol analysis. At the end of six growth experiments animals were slaughtered. Liver vitamin-A concentration of calves depends on their term at birth and is associated with the carotene intake of their mothers. The carotene content of feeds and the vitamin-A supply are the most important influencing factors on liver vitamin-A concentration of growing and lactating cattle. On the average, livers of calves fed with colostrum contained 100-200 IU, those of growing cattle fed with grass and legumes or with silages contained 200-300 or 100-200 IU resp., and those of cows fed with green fodder or silage contained 300-600 or 100-300 IU vitamin A resp. per g fresh liver. There were also values outside of the variations mentioned above. The vitamin-A storage capacity of liver and the effects of oral and parenteral vitamin-A supply to depleted calves and growing cattle were also tested.