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The article covers the study of the effect of β-lactoglobulin gene polymorphism on daity productivity, qualitative composition of milk and lactation activity of Holstein cows. The work was carried out on 146 animals in the Lenin Breeding Farm Integrated Agricultural Production Center (IAPC) of the Republic of Tatarstan. DNA genotyping by the locus of the Bos taurus BLG-Hae III gene was performed by PCR-RFLP. As a result of genetic typing of cattle, 2 alleles (A – 0.651 and B – 0.349) and 3 genotypes (AA – 41.1, AB – 47.9 and BB – 11.0 %) were identified. The chi-square criterion is below the critical value (5.99; p < 0.05) and testifies that the Hardy-Weinberg genetic equilibrium is not disturbed in the population. The evaluation of dairy productivity traits showed that cows with the AB genotype have the highest milk yield and high-quality milk. The heifers with the AB genotype are characterized by the best lactation curve throughout lactation. The difference in the amount of milk received between cows with the AB genotype and animals with the AA and BB genotypes is 71.6 kg (or 9.3 %) and 95.7 kg (or 16.9 %), respectively. Cows with low milk yields (genotype AA) had the lowest lactation decline (4.34) and greater stability (99.9).

The study examined the polymorphism of the glutathione peroxidase-1 gene (GPX-1, g. 189 T/C) effect on the GPx enzyme activity and biochemical parameters in the blood serum of Holstein cows of indigenous and foreign selection. The work was carried out in the Lenin Breeding Farm Integrated Agricultural Production Center (IAPC) and the Mukhametshin Z.Z. Peasant Farm Enterprise (PFE) of the Republic of Tatarstan. DNA genotyping by the locus of the Bos taurus GPX-1-Bsc4 I gene was performed by PCR-RFLP. As a result of genetic typing of cattle, 2 alleles (C and T) and 3 genotypes (CC, TC and TT) were identified. The classification carried out by PIC values in two populations of Holstein cattle showed that there is a moderate polymorphism of the GPX-1 gene. A negative inbreeding coefficient (F) indicates excessive outbreeding in both populations. In both populations, the numerical advantage of heterozygous genotype TC cows is 60.1 and 56.7 % of the total livestock. Indigenous breeding cows, compared with imported cattle had higher: GPx activity, AST, ALT, cholesterol level, total protein and albumin fraction. Analysis of the association between the GPX-1 gene polymorphism and the GPx enzyme level indicates that the activity of this enzyme varies depending on the genotype, and there is also a variation in the biochemical parameters of the Holstein cattle blood serum.

The aim of the work was to study serum biochemical parameters and qualitative composition of milk of cows with various genotypes of the LEP gene. The research was conducted in 148 Holstein cow-heifers of Integrated Agricultural Production Centre “Stud farm named after Lenin” of the Atninsky district of the Republic of Tatarstan. Cattle genotyping was conducted by the AC-PCR method at the laboratory of the Department of Agrobiological Research of Tatar Research Institute of Agriculture of FRC KazanSC of RAS. The findings of allele and genotype calling of the LEP gene showed that the population under study is polymorphic and differs in genetic biodiversity. The study of serum biochemical parameters of experimental animals testified that the level of triglycerides, cholesterol and lipase is meaningfully lower in the blood of animals with the TT genotype. This indicates the rate of lipid metabolism in their body. During the analysis of milk productivity and parameters of the qualitative composition of milk, it was found that cow-heifers with the TT genotype of the LEP gene were superior to animals with other LEP gene genotypes in terms of milk yield for standard lactation (305 days), fat mass fraction, milk fat yield, milk fat and milk protein yield in total. Thus, it may be concluded that the TT genotype of the LEP gene has a positive effect on the economically important characters of cattle, which can be used in breeding in the future.

The aim of the work was to study the traits of dairy productivity of Holstein heifers with different genotypes of the paraoxonase-1 (PON1) gene. The research was conducted in 148 animals of Integrated Agricultural Production Centre “Stud farm named after Lenin” of Atninsky district of the Republic of Tatarstan. Genotyping of cattle was carried out by the PCR-RFLP method at the laboratory of the Department of Agrobiological Research of Tatar Scientific Research Institute of Agriculture, FRC Kazan Scientific Center, Russian Academy of Sciences. The results of allele and genotype calling of the PON1 gene showed that the study population is polymorphic and differs in genetic biodiversity. During the analysis of daity productivity, qualitative composition of milk and lactational activity, it was found that cow-heifers with the GG genotype of the PON1 gene were superior to animals with other genotypes in all the test parameters. Thus, it follows that the GG genotype of the PON1 gene has a positive effect on the economic characters of cattle, which can be used in breeding in the future.

The research presents the findings of DNA testing of allelic polymorphism by the PCR-RFLP method of the SCD1 gene and the relationship of genotypes with the milk fatty acid composition of Holstein cows of Tatarstan population. The research was conducted among 172 Holstein cows at the Integrated Agricultural Production Centre “Stud farm named after Lenin” in Atninsky district of the Republic of Tatarstan in 2017–2018. All genotypes of the SCD1 gene were identified through the research. The milk yield test showed that the maximum content of the mass fraction of fat was in animals with the TT genotype. The significant difference between the content of the mass fraction of fat in milk in individuals by the locus of the SCD1-Fsp4H I gene was: TT to CC – 0.32 % (p < 0.05) and TT to TC – 0.40 % (p < 0.01). The results of chromatography indicate the balance of the milk fatty acid composition of cows with the TT genotype and, as a consequence, its positive effect on the human body. Cows with a homozygous TT genotype are characterized by the optimum ratio of fatty acids in milk fat. The maximum value of the oxygen desaturation index is also observed in animals with the TT genotype by the SCD1 gene.

The research presents the findings of DNA testing of allelic polymorphism by the AC-PCR method of the LEP gene. The research was conducted among 172 Holstein cows at Integrated Agricultural Production Centre “Stud farm named after Lenin” in Atninsky district of the Republic of Tatarstan in 2017–2018. All genotypes of the LEP gene were identified through the research. Associations of the leptin gene polymorphism with dynamics of milk production during three lactations of Holstein cows were established. The best indicators for all three lactations were found in a group of animals with the TT genotype of the LEP gene. These individuals are characterized by increased milk yield, a high yield index, and tend to increase the average daily milk yield during three lactations. These individuals are characterized by increased milk yield, a high milk yield index, and tend to increase the average daily milk yield during three lactations.

The study presents the results obtained in DNA testing of allelic polymorphism by PCR-RFLP based methods for the leptin and stearoyl-coenzyme A desaturase genes and the interaction of their complex genotypes on the milk productivity indicators of Holstein heifers of Tatarstan population. The study was carried out among 471 Holstein cow-heifers by Integrated Agricultural Production Centre “Stud farm named after Lenin” of Atninsky district of the Republic of Tatarstan in 2016–2018. All complex LEP/SCD1 genotypes were identified through the study. The maximum frequency was observed in the combination of heterozygous genotypes LEPTCSCD1TC 149 animals (31.5 %). Milk productivity test, based on the complex genotypes LEP and SCD1, showed that a significantly high level of productivity for 305 days of lactation was 7314.4 kg, and in heifers with a complex genotype LEPTTSCD1CC was minimal (6337.4 kg) in comparison with indicators of milk yield of heifers with other complex genotypes. According to the content of the mass fraction of fat, reliably the best indicators were established in a subpopulation of animals with a complex TT/TC genotype 3.87 %. The content of the mass fraction of protein was maximal for animals with a complex CC/CC genotype.