Features of regression dependence of signs in cows of holstein breed of different selection
It has been used general zootechnical methods (individual accounting of milk productivity, reproductive capacity), laboratory (determination of the quality of milk), variation-statistical method (regression analysis) during the research process. The material of the study was the data of milk productivity and reproductive capacity of cows of two generations of German Holstein breed (n = 362) and Ukrainian (n = 350) selection. The comparative analysis showed that the cows of the Holstein breed of German selection were characterized by lower regression coefficients of traits of milk productivity, except for the protein content in milk, than the animals of the Holstein breed of Ukrainian selection. At the same time, we observe a negative regression dependence on the fat content in milk (bD/M = -0.182), which can be explained by the changes that occur in the process of adaptation of imported cattle to new technological conditions of operation. The cows of Holstein breed of Ukrainian selection set straight regression dependence of milk signs production, yield during 305 days of lactation (bD/M = 0.274), the amount of milk fat (bD/M = 0.279) and the number of milk protein (bD/M = 0.258 ), the amount of milk fat per lactation (bD/M = 0.227) and per day (bD/M = 0.295). It is established that cows of Holstein breed of German selection, despite existence in different natural-climatic and forage conditions, keep not only a high level of productive signs, but also reproductive ability. According to the results of regression analysis, the presence of a rectilinear dependance between both breeding signs and individual traits in related groups of animals (daughter-mother) has established. This, in turn, allowed clarifying the effectiveness of selection in the formation of a highly productive herd of Holstein breed, which occurs through the introduction of uterine livestock and the use of bulls-breeders. A comparative analysis of the regression coefficients of productive signs of Holstein cows of Ukrainian selection revealed that more attention is paid to increasing milk yield in animals and due to this there is an increase in milk fat and protein in daughters which came from mothers of different productivity levels. According to the results of regression analysis, it was found that the selection of Holstein dairy cattle in increasing protein milk yield should be continued, as selection for fat milk production will be much less conducive to increasing the protein content in milk.
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