Changes in the genotypic structure of cows, yield of milk, fat and protein, fat and protein content of milk, relationships between milk components, i.e. the protein to fat ratio (PFR) and the difference between fat and protein content (DFP) were examined using data from the Polish Federation of Cattle Breeders and Dairy Farmers for 2001–2009. In addition, analysis was made of changes in the length of calving interval and age at first calving. Average yield of milk and its components was found to increase in all milk recorded cows. Changes in the relationship between basic milk components differed between the breeds. A decrease in fat content was found in the milk from Polish Black-and-White Holstein-Friesian, Jersey, Montbeliarde and Polish Red-and-White cows, and an increase in protein content was recorded in the milk from Polish Black-and-White Holstein-Friesian, Polish Red-and-White, Simmental and Montbeliarde cows. These changes had a favourable effect on the PFR ratio in Polish Holstein-Friesian cows, especially those of the Black-and-White variety. Calving interval and age at first calving were found to increase in all the cows except the Montbeliarde breed.
