The aim of this study was, on the one hand, to analyze changes in milk productivity and milk quality indicators in cows throughout lactation and, on the other hand, to determine the optimal timing of test-day milkings for milk sampling in order to obtain the most accurate prediction for standard lactation. The study was conducted at the agricultural enterprise “Molocharske” in the Pokrovskyi district of Dnipropetrovsk region using Holstein cows. It was established that the maximum daily milk yield in Holstein cows was observed on the 50th day of lactation, after which a gradual decline in daily milk production occurred until the end of lactation. Significant negative correlations were found between milk yield and fat content (r = -0.32; p≤0.001), as well as between milk yield and protein content (r = -0.28; p≤0.001). At the beginning of lactation, the fat-to-protein ratio was elevated, indicating a negative energy balance during this period. In the second half of lactation, an increase in the number of somatic cells in milk was observed. At the same time, a signifi cant positive relationship was established between somatic cell count and protein content (r = 0.19; p≤0.05). Meanwhile, lactose content showed a negative correlation both with somatic cell count (r = -0.38) and protein content (r = -0.22). The energy-corrected milk (ECM2) yield decreased from 33.44 to 21.51 kg throughout lactation and showed a strong significant correlation with daily milk yield (r = 0.91; p≤0.001), confi rming its informativeness for the comprehensive assessment of milk productivity. The highest correlation coefficients between the results of test-day milkings and productivity indicators for standard lactation were established for the 3rd–6th test-day milkings. This indicates the feasibility of using this particular lactation period for the most accurate prediction of 305-day productivity. At the same time, fat content determined at diff erent stages of lactation correlated more weakly with the average lactation value compared with other traits, which reduces the accuracy of its prediction based on individual daily indicators.

Keywords: dairy cows, productivity prediction, milk yield, fat and protein content, somatic cells.