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The investigations were conducted on 18 heifers from the birth to conception, and on 16 cows from the conception to the end of the first lactation. The levels of some blood indices (total protein, protein fractions, urea, erythrocytes, leucocytes, haemoglobin, haematocrit) were examined every month. There was obtained a high agreement between the data collected by the present writer and those published by other authors. Significant changes in the level of total protein and of protein fractions in blood serum were observed mainly at the beginning of the growth period, at the end of pregnancy and in the first months of lactation. The morphological appearance of peripheral blood showed high variability during the growth period in heifers, but more stability during pregnancy and lactation in cows. The variability of the urea levels in blood serum depended more upon feed rations than on the stage of growth, on pregnancy or lactation.