The causes of diseases and their intensiveness in calves and calves post the vealer stage were the subject of the studies and included over 2700 male calves of Red-White and Black-White breeds with different contribution of genes of hf breed. In years 1986—1990 over 40 per cent animals suffered from diseases of the respiratory tract with an increasing tendency in animals with a higher contribution of hf genes. In order to maintain a normal cycle of production 76 per cent male calves of Red-White breed and 70 per cent calves of Black-White breed were scrapped. There was found a different percentage of infections (24—100 per cent) of calves in various groups of paternal half-brothers.