Influence of Production Season and Lactation Stage on the Technological Suitability of Milk from Cows of Various Breeds Fed in the TMR System

The aim of the study was to evaluate selected indicators of the technological suitability of milk from four breeds of cow housed in free-stall barns and fed in a TMR system. A total of 1, 146 milk samples were analysed, collected from cows of the breeds Polish Holstein-Friesian (Black-and-White and Red-and-White populations), Jersey, and Simmental. The following were determined in the samples: content of solids non-fat and casein, protein-to-fat ratio, active and potential acidity, heat stability, rennet clotting time, and milk fat dispersion. Despite the use of a mono-diet (TMR) year round, somewhat higher daily milk yield was obtained in the spring/summer season, but the differences were statistically significant (P≤0.01) only in the case of PHF RW. The milk obtained in the autumn/winter season contained more solids-non-fat, including casein, and in the case of JE and PHF HO the differences were statistically significant (P≤0.01). It also had significantly higher heat stability and a longer rennet clotting time (P≤0.01), with the greatest differences noted in the case of the SM breed. Milk from this period also had a higher percentage of fat globules with a diameter. 6 ≥m. The concentration of solids-non-fat, including casein, increased significantly (P≤0.01) over the course of lactation in all of the breeds evaluated. The stage of lactation did not significantly affect clotting time, heat stability, or milk fat dispersion.