Abstract
We researched the influence of two methods of housing primiparous cows on meeting estimated energy requirements. In herd A primiparous cows were kept in a separate technological group during the whole lactation period, whereas in herd B they were kept in technological groups together with multigravid cows. The whole herd A consisted of 400 cows, where the average annual yield was 10,200 kg of milk per cow. Herd B consisted of 250 cows, where the average annual yield was 8,500 kg of milk per cow. In 2010 and 2011 there were 200 primiparous cows in herd A, whereas in herd B there were 165 primiparous cows. The milk yield for 100 and 305 days of lactation was analysed. Meeting the cows’ demand for energy was determined on the basis of the percentage of protein in milk. In both herds primiparous cows were divided into milk yield classes for 100 days of lactation. Both the trend and the amount of variation in the content of protein in milk were found to be identical in both herds. The content of protein in milk increased as the milk yield decreased. This regularity could be observed at both lactation stages under analysis and the differences between the classes were statistically confirmed. During the first 100 days of lactation the estimated energy deficit comprised a much larger percentage of the cows than in the 305-day lactation period. The system of maintenance of primiparous cows (separately or together with multigravid cows) was not found to influence the milk yield or the estimated demand for energy