Evaluation of milk composition and yield in active populations of Black-White and Red-White primiparous cows in Poland

Active populations of crossbreeds of Slack-White (BW) x HF and Red-White (R W) x HF primiparous cows were superior to pure-bred BW and RW peer groups i n terms of milk yield and its composition during a period of 305 lactation days irrespective of the percentage that they had of HF genes: Both RW pure -breds and :crossbreeds had a slightly better protein to fat ratio (SBT) an d a smaller difference between fat and protein milk content (RTB) when comp ared to BW and BW x HF populations: There was a smaller difference between fat and protein content (RTB) and more favourable protein to fat. ratio (SB T):amongst pure-breds of the Black and White breed compared to their HF pur e-bred contemporaries.