The relevance of research. Currently the methodological base for assessing the breeding qualities of bulls-producers of dairy and milk-meat breeds by the quality of offspring is carried out in accordance with the Instruction approved by the MA of the Republic of Kazakhstan in 2007. The principle of assessment, set out in the Instruction, is to compare the phenotypic indicators of the offspring with each other according to the principle of “peer daughter”. Although this document was approved already in the XXI century, nevertheless the basic approaches, which were put the basis, were developed in the first half of the last century and currently do not correspond to modern scientific principles. At the same time the world leaders in the field of breeding in dairy cattle breeding have been successfully using the BLUP method in breeding practice to assess the breeding qualities of animals for decades. This principle of assessing the breeding value of bulls is the most theoretically grounded and allows you to obtain results comparable to each other. Therefore the development and optimization of the equations of mixed BLUP models is extremely relevant for the conditions of the Republic of Kazakhstan from both scientific and practical points of view.Material and research methods. The material of the research was the data on the phenotypic indicators of the signs of milk productivity of first-calf cows of the Holstein black-and-white breed obtained from the republican database of the Republic of Kazakhstan for 2016-2017. As a criterion for choosing the best equation the residual variance values of each model under study were used.Results: when improving the method for assessing bulls-sires of the Holstein black-and-white breed according to the quality of offspring, out of the four studied equations of the mixed BLUP model one equation was optimized to assess the breeding qualities of the sires. In principle, to assess the breeding qualities of producers by the quality of offspring it is possible to use any of the models under consideration, since the established differences for all analyzed characteristics of milk productivity are insignificant (no more than 6%)

The aim of the research was to estimate the breeding value of the servicing bulls of the Holstein black-and-white breed according to the optimized equation of the mixed BLUP model. Within a comparative aspect, the estimation results of bulls calculated using the BLUP methodology are presented. As an object of the research, information was used on first-calf heifers (daughters of the evaluated bulls), who lactated in breeding herds of the Holstein cattle of the Republic of Kazakhstan in 2016-2017. The source was the official information analytical system (IAS) of livestock breeding of the Republic of Kazakhstan. The analysis of information on the dairy productivity of the cows-daughters of the estimated bulls was performed according to the indicators of the milk yield, the contents of fat and protein in milk, the milk fat and protein yield for 305 days of lactation and the study period. To compare the obtained results, the average values of breeding value indices, the reliability of their assessment, and the rank correlation coefficients were calculated

According to the current “Instruction” used in dairy cattle selection and breeding in the Republic of Kazakhstan, bulls-producers of dairy breeds are assessed according to the their offspring quality based on the principle of “peer daughter”. This means that the phenotypic indicators of the daughters of the tested bulls are compared with the corresponding indicators of their peers. In European countries with developed dairy cattle breeding, as well as in Canada, the USA, etc., to ensure a reliable forecast of the genetic value of individuals (primarily, bulls-producers), use is made of the best linear unbiased forecast method (BLUP method). This method implies that the breeding value of producers is determined by the deviation values of the development of traits of the examined animal from its average values in the population. Especially urgent area is the research aimed at improving breeding programs, including assessing the breeding value of bulls-producers of dairy breeds using BLUP methods based on the productive qualities of the mass of dairy cattle in the Republic of Kazakhstan. The research material included the data on the phenotypic indicators of the milk productivity of first-calf cows (the amount of milk yield, the content of fat and protein in milk, the yield of milk fat and protein) of the Holstein black-motley dairy cattle breed, obtained from the information and analytical database of the Republic of Kazakhstan for 2016–2017. It was found that when evaluating according to the official “Instruction”, 16 sires out of 256 bulls (6.2%) got the stud category in 2016, 14 sires (9.2%) out of 152 bulls in 2017, and – 30 sires of 249 bulls (12.0%) over the cumulative period. The results of the conducted research prove that the use of the classic “Instructions” in dairy cattle breeding has lower efficiency (by 42.8–90.0%) as compared with the assessment of the breeding value of bulls based on the BLUP method.The selection of sire bulls into breeding groups based on the “peer daughter” methodology is not reliable enough and rather ineffective. Comparing the results of assessing the breeding qualities of sire bulls, obtianed using two methods in all compared periods (2016, 2017, 2016–2017), the authors established a clear superiority of the BLUP method over the current Instruction used in the Republic of Kazakhstan.