IMPACTS OF LACTATION PHYSIOLOGY AT HIGHER AND AVERAGE YIELD ON COMPOSITION, PROPERTIES AND HEALTH INDICATORS OF MILK IN HOLSTEIN BREED

Milk yield (MY) is the amount of milk and its quality during lactation. MY is an important economic and health factor closely connected with the health status of dairy cows, their reproduction, performance, longevity and milk composition and properties. The differences within milk indicators between high yielding herds with an average MY (H1 a H2) were tested in four herds. The files with 224 and 234 individual milk samples were collected in the summer and winter for three years. The files were balanced in factors of lactation. Group 1 had higher genetical value and had even better nutrition according to the MY. The MY was higher by 43% (P ≤ 0.001). The studied high MY factor had statistically significant influence (P ≤ 0.05 and P ≤ 0.001; Table 1; Fig. 1) on the following milk parameters: fat (FAT), lactose (LAC), solids non fat (SNF), alcohol stability (AL), rennet curds firmnes (RCF), crude protein (CP), casein (CAS), true protein (TP), fat/true protein ratio (F/CP). Selected differences were: FAT (H1 3.68 ± 0.77; H2 3.99 ± 0.93%); CAS (H1 2.50 ± 0.27; H2 2.59 ± 0.29%); TP (H1 2.99 ± 0.30; H2 3.09 ± 0.33%). Other 16 milk parameters (e.g. SCC (H1 289 210 103.ml^–1 H2), urine, ratio of urea nitrogen in the non protein nitrogen, acetone, pH and rennet curds firmness) were influenced insignificantly (P 0.05). The differences in milk indicators between group H1 and H2 did not indicate problems of the health status. The high MY reached by the genetic improvement of animals does not result in impaired quality of raw milk. Surprisingly, MY and urine content in milk did not correlate positively in Holstein dairy cows