EN
Holstein-Friesian cattle, which is currently considered as the best dairy cattle in the world, originates from Black-and-White European cows brought in large amounts to America in 1852-1905. Breeders all over the world found the advantages of American Holstein-Friesans which resulted in importing this cattle to nearly 100 countries on all the continents. The first batch of HF bulls' semen,vas brought to Poland in 1971 and in 1973-1976 as many as 353 heifers were imported from the USA and Canada. An experiment comparing genetic values of 10 Friesian varieties with regard to their milk and beef utility, carried out in Poland in 1974-1984 under the FAO auspices, had a considerable impact on the worldwide breeding of Friesian Black-and-White cattle. It was indicated that the off spring of HF bulls from the USA, Canada and Israel,vere distinct from the European varieties (Denmark, Holland, West Germany, Sweden, Great Britain) as weil as from a New Zealand' s one: their growth rate and body size were bigger, udder construction more appropriate and, first and foremost, the milk yield was higher by 20% at slightly lover fat content. A wide use of HF bulls' semen in Poland (starting from mid 80s) in the insemination of cows and heifers has led to fundamental changes in home population of BW cattle. At present, nearly 90 per cent of Black-and-White heifers evaluated in Poland are crossbred with HF and a half of this figure have over 50 per cent of HF genes. Improving Polish Black-and-White cattle by means of Holstein-Friesian bulls significantly influences changes in body build of the animals and their milk productivity what consequently leads to the transformation of this population into one-sided milk type. The unfavourable effects of this improvement are certain changes in the frequency of genes conditioning the polymorphism of some milk proteins in cows as well as lower rates within beef utility in young bulls crossbred with HF.