[Differences in the milk yield with reference to the standard and factual duration of lactation in different lengths of the calving period].

Attempt is made to elucidate and evaluate the difference in the milk yield on a total and per day basis during the calving period at both actual and standard lactation period. It was found that at duration of the calving interval that was admittedly shorter than the standard -- 365 days -- the cows had shorter lactation period than the standard one. At duration of the calving interval of 360 to 370 days (365 days on a average) which is standard for this country none of the groups of cows reached the normative duration of the claving period in terms of milk-yielding capacity. This was better expressed also with the lengthening of the calving period over 365 days. When the cows fail to reach the standard (normative) duration of the lactation period considerable amounts of milk are presumably lost -- for 300 days of lactation, -both for the lactation period as a whole and for each single day of the calving period.