[The level of beta carotene and vitamin A in blood plasma of calves during the 1st four-month postnatal period].

Calves of the Bohemian Spotted breed were studied for the levels of vitamin A and beta-carotene in blood plasma. The total number of calves (204) was divided into 17 age categories differentiated by a one-week interval. Until the average age of 13.48 days the calves were fed by sucking their mothers' colostrum and milk. After weaning and transfer to the calf-house the animals were reared on a milk feed mixture for calf rearing (Laktosan). Other feed ration components were gradually included in the diet: hay, the TG mixture supplement, root crops, and green forage. The study was performed during the period from June to October. Throughout the experimental period, the levels of vitamin A remained above the values mentioned in literature as levels connected with the manifestations of hypovitaminosis. The minimum average vitamin A level was 15.49 microng per 100 ml and the maximum average level 32.36 microng per 100 ml of blood plasma. The level of beta-carotene in plasma was high in the first two post-natal weeks (maximum 246.12 microng per 100 ml). In the subsequent period it dropped to extremely low values (lower than 10 mg per 100 ml). Only when green forage was included in the feed ration, the level of beta-carotene increased significantly. The content of vitamin A in the calf-rearing milk feed mixture guarantees its sufficient level in the blood of healthy calves. Colostrum and milk as important beta-carotene sources, are replaced in this function by green forage in the later period of calf development.