The aim of the work was to determine the effect of the age of the first calving on milk performance in the 1st, 2nd and 3rd lactation, the sum of yield of milk, fat and protein for three complete lactations and the amount of the mentioned components as calculated per one day of life. The age of the first calving had a significant infl uence on milk yield only in the first lactation. The percentage fat content did not differ significantly between the groups of the age of calving whereas the studied factor affected significantly the protein content in milk of the cows after the second and third calving. The obtained results indicate that the most favorable economically mating of heifers takes place until the 27th month of life as such animals give the greatest quantities of milk, fat and protein, as calculated per one day of life.
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