Impact of successive lactation, year, season of calving and test milking on cows’ milk performance of the Polish Holstein-Friesian Black-and-White breed

The research was conducted based on 8895 test milkings of 463 milk cows calving first time in 2003 and reared in the Pomorze and Kujawy region. The aim of the present study was to analyse the influence of selected factors on the milk performance and its chemical composition. A statistical influence of a herd, season and year of calving, a season of test milking, lactation on milk performance traits was analysed using a multiple variance analysis. The milk performance, its chemical composition and quality altered considerably depending on the season of calving, season of test milking and successive lactation. The highest percentage amount of milk and its components was obtained from cows calving in spring months. In turn, the highest content of fat, protein, lactose and dry matter occurred in the samples collected from the cows calving in the summer milking period. The highest amounts of milk were collected in the summer period, and the lowest – in the winter period (these dissimilarities proved highly significant). The highest amount of calculated FCM and ECM, fat (kg) and lactose was collected from cows in their first lactation, whereas the lowest from those in their fourth lactation