MILK PRODUCTIVITY OF COWS UNDER DIFFERENT OPTIONS OF PARENTAL PAIR SELECTION

Introduction. One of the main ways to improve dairy herds is through the identification and utilization of the most effective combinations of parent pairs. This can be achieved by both within-line selection and crossbreeding. It is important to identify the most promising lines and their optimal combinations to ensure their effective utilization for further herd improvement. According to many authors, a systematic approach that involves identifying successful and unsuccessful combinations with the repeated use of the most effective variants will reliably contribute to the increase of the genetic potential of dairy cattle productivity. Materials and methods of research. In light of the above, the aim of our research was to investigate the formation of milk production traits in Ukrainian Black-and-White dairy cows in different farms of Ukraine, depending on various options for parent selection. The research was conducted on first-calf heifers and mature cows (third lactation) of Ukrainian Black-and-White dairy breed in three farms: SE EF "Oleksandrivske" in Vinnytsia region (Forest-Steppe zone, n = 714), LLC AE "Imeni Volovikova" in Rivne region (Polissya zone, n = 1840), and SE "Experimental farm "Askaniyske" in Kherson region (Steppe zone, n = 926). The sample included cows that had completed at least the third lactation during the research. In the study animals, the milk production traits (milk yield, milk fat content, and milk fat yield) were studied based on various options of within-line and between-line parent selection through retrospective analysis of zootechnical records data over the past ten years. Research results. The analysis of between-line selection of Ukrainian Black-and-White dairy animals in SE EF "Oleksandrivske" showed that the most successful combinations for milk yield and milk fat yield in first-calf heifers were when the dams belonged to the Valiant line and the sires belonged to the Chif line. For mature cows (third lactation), the most successful combinations were when the dams belonged to the Eleveishn line and the sires belonged to the Starbuck line. The lowest values of the mentioned traits for the studied lactations were observed in cows obtained from the crossbreeding of the R. Meximes-Chif and S. T. Rokita-Chif lines, respectively. In LLC AE "Imeni Volovikova", the most productive animals for the first lactation were those obtained from the combination of the Starbuck-Bella lines, while for the third lactation, the individuals derived from the crossbreeding of the Bella-Chif lines showed the highest productivity. The least successful combination for both studied lactations was when the dams belonged to the S. T. Rokita line and the sires belonged to the Bella line, as animals resulting from this crossbreeding had the lowest milk yield and milk fat yield values. SE "Experimental farm "Askaniyske", the highest milk yield and milk fat yield values for the first lactation were observed in individuals whose dams belonged to the Seateischna line and the sires belonged to the Starbuck line. For the third lactation, the highest values of the mentioned traits were found in cows obtained from the combination of the Chif-Starbuck lines. The lowest productivity for the mentioned lactations was observed in cows resulting from the crossbreeding of the R. Sovering-Bella and R. Sovering-Chif lines, respectively. In the internal line breeding at the SE EF "Oleksandrivske," the most productive individuals were found to be first-generation offspring whose parents belonged to the Chief line, and mature cows from the Starbuck line. In the LLC AE "Imeni Volovikova" the animals from the Bella line showed superior performance in both lactations. In the SE "Experimental farm "Askaniyske" cows from the Eleveishn line were found to be the most productive. Regarding milk fat content in the Forest-Steppe zone, the best performers were first-generation offspring resulting from the combination of the Cavalier-Chief lines, as well as mature cows from the Eleveishn-Starbuck cross. In the Polissya zone, animals obtained from the Eleveishn-Bella and Starbuck-Bella crosses showed the highest milk fat content. In the Steppe zone, first-generation and mature cows whose mothers belonged to the R. Sovereign line and fathers belonged to the Chief and Bella lines, respectively, demonstrated superior traits. Conclusions. Thus, improvement of economically important traits in animals can be achieved through both internal line breeding and interline breeding. In this regard, it is crucial to identify the best line combinations and effectively utilize them in further breeding work.