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The article presents the results of the assessment of the biological usefulness of feed according to the control tests of milk. Scientific research was carried out in LLC "Minskoye" of the Kostroma district of the Kostroma region on a population of 369 cows of the Kostroma and Black-and-White breeds according to the seasons of the year. The authors found that in terms of the level of digestible protein in lactating cows, there is an imbalance in almost all seasons of the year, so most animals are prone to diseases associated with metabolic disorders. The level of rumen acidity in animals of the Koroma breed was more stable (pH = 6.2-6.4) in all seasons of the year, which indicates a lower likelihood of developing acidosis, in contrast to Black-and-White breed cows. Based on the indicators of milk control tests, insufficient supply of raw protein to cows of the Kostroma and Black-and-White breeds during the milking period was established. The highest daily milk yields (more than 30 kg of milk) were obtained from cows in the first and second periods of lactation in all seasons of the year. In animals with a level of availability of digestible protein of 10.3-10.9 g/MJ, there is a normal ratio of fat: protein (1.26:1), with a profitability level of 66.11%, while animals with an insufficient level availability of digestible protein of 10.2 g/MJ and less, had the level of profitability of milk production 73.93 and 86.44%, respectively. When the level of availability of digestible protein is more than 11.0 g/MJ in animals, the likelihood of acidosis increases. Evaluation of the biological value of feeds according to control tests of milk during the period of control milkings will allow monitoring the energy and protein nutrition of animals.

The article reflects the current state and the prospects of the Kostroma cattle breed development. The creation and improvement of the breed anticipated the formation and further breed development in the domestic and world zoo technical science. In recent years, the number of Kostroma cattle breed has been unreasonably reducing despite its economic valuable traits. At the same time in the Kostroma region there are prospects for preserving the valuable gene pool of one of the best domestic dairy and meat cattle breeds. As a result of directed selection and breeding work with the use of Brown Swiss bulls, a stud milk breed "Karavaevsky KK-1" has been developed. At present cow-champions of the Kostroma breed give up to 12,000 kg of milk per lactation. The milk of the Kostroma breed cows has a high content of protein and fat. The animals of Kostroma breed have good meat qualities, high resistance to a number of diseases, strong ungulate horn, easy adaptability to intensive technologies, good fertility and high productive longevity. To save the Kostroma breed it is important to put on 8-10 bulls of 8 planned lines and related groups for the validation and accumulation of sperm every year. The restoration of previously created lines with high genetic potential should be foreseen. It is necessary to identify and actively use the stud bulls bred in their own breeding farms; to conduct a linear assessment of bulls and daughter heifers by body type for more competent selection. In addition to the generally accepted forms and methods of selection, it is necessary to continue immunogenetic control of the authenticity of the origin of breeding animals and introduce modern methods of DNA technology to assess the breeding and productive qualities of cattle, which will reveal valuable genetic complexes in the best breeding animals and thus 1.5-2 times accelerate the selection processes.Conflict of interest: the authors stated that there was no conflict of interest.