The Power of the Influence of the Genotypes of DNA Markers on the Indicators of Milk Production of Cows

The purpose of the work was to study the power and reliability of the influence of the genotypes of kappa-casein (CSN3), diacylglycerol O-acyltransferase (DGAT1), somatotropin (GH), prolactin (PRL) on the indicators of milk production of black-and-white cattle. It was revealed that the CSN3 genotype had the greatest significant influence on the mass fraction of protein in milk, the proportion of its influence was ?2 = 0.353 (Ffactual= 40.323; P<0.001) in first-calf heifers and it was ?2= 0.140 (Ffactual= 13.400; P<0.001) in full-aged cows. There was also found an influence on milk protein yield that was ?2= 0.074 (Ffactual= 5.882; P<0.01) and ?2= 0.039 (Ffactual= 3.390; P<0.05). The DGAT1 genotype had a highly significant effect (P<0.001) on the fat mass fraction in milk for the 1st lactation ?2= 0.189 (Ffactual= 17.202), for the 3rd lactation ?2= 0.109 (Ffactual= 10.101). According to the somatotropin gene, a significant degree of influence of the genotype was revealed in full-aged cows only by milk yield per lactation ?2= 0.057 (Ffactual= 4.949; P<0.01), and by the prolactin gene in terms of fat content of milk ?2= 0.044 (Ffactual= 3.822; P<0.05). The desired allele B of the CSN3 gene has a significant effect only on the mass fraction of protein ?2= 0.342 with the maximum value of the Fisher criterion that is Ffactual= 26.489 (P<0.001), and the allele K of the DGAT1 gene on the mass fraction of fat in milk ?2= 0.163 (Ffactual= 17.305; P<0,001) and the V allele of the somatotropin gene on milk protein yield ?2= 0,097 (Ffactual= 3.641; P<0.05). The genotypes CSN3 and DGAT1 have the widest influence on the indicators of milk production of cows.

Effective selection work in dairy cattle breeding is possible only with the integrated use of zoo technical methods and modern DNA technologies. The use of molecular genetic methods for early prediction of the magnitude and direction of the productive qualities of an individual increases the rate of breeding progress by half and contributes to obtaining a significant economic effect [1]. The use of genetic markers in cattle breeding responsible for milk production will improve the economically useful characteristics of cows. Alleles of genes of milk proteins; hormones and enzymes are considered as potential DNA markers of milk production and milk quality in cattle. Some of these markers are genes for kappa-casein and diacylglycerol O-acyltransferase; somatotropin; prolactin [2-3]. Nowadays a special attention is paid to the gene locus of one of the main milk proteins that is kappa-casein. It is known that allelic variants of the milk protein of kappa-casein are connected with indicators of protein content of milk; and the yield of milk protein by the technological properties of milk [4-7]. Diacylglycerol O-acyltransferase (DGAT1) gene involved in fatty acids metabolism. DGAT1 gene of cattle is mapped to the centromeric side of chromosome 14. Studies of Russian and foreign authors have revealed that this mutation significantly affects the milk production of cows; in particular; the milk yield and fat content of milk. At the same time it has been established that allele A is associated with high milk production and allele K is associated with a high content of mass fraction of fat in milk [8-11]. The use of hormone genes - prolactin (PRL) and somatotropin (GH) as DNA markers of milk production in cattle is connected with the participation of proteins encoded by them in the regulation of lactation; synthesis and secretion of various constituents of milk [12-13]. Thus; cows with the BB genotype for the prolactin gene have a higher fat content of milk and; accordingly; have a higher yield of milk fat and protein [14-15]. The influence of various allelic variants of the GH gene on the indicators of milk production of cows (milk yield; fat and protein content of milk) was also determined [16-18]. The issue of improving the productive qualities of cows is a daily problem and is based on a combination of genetic and non-genetic factors. As a consequence; an important problem arises of studying the proportion of the influence of different genotypes of DNA markers on the productive qualities of dairy cattle. In this regard; the purpose of the work is to study the power and reliability of the influence of the genotypes of kappa-casein; diacylglycerol O-acyltransferase; somatotropin and prolactin on the indicators of milk production of black-and-white cattle.

In order to conduct the research and genotyping for kappa-casein; diacetylglycerol O-acetyltransferase; somatotropin; prolactin 151 first-calf heifers and 168 full-aged black-and-white cows; from which blood samples were taken and DNA samples were isolated; were selected in the conditions of the breeding reproducer of OOO «Dusym» (Dusym; LLC) of Atninsky District in the Republic of Tatarstan. The material for molecular DNA testing was the venous blood of animals. DNA isolation was carried out using the Magnosorb kit (Interlabservice; Moscow); according to the manufacturer's instruction. Genotypes CSN3; DGAT1; GH; PRL were determined by PCR-RFLP (restriction fragment length polymorphism). Amplification was carried out on a Tertsik amplifier (DNA-technology; Moscow). Depending on presence of alleles A and B of the CSN3 gene; genotypes were divided into three groups (AA; AB; BB); alleles A and K of the DGAT1 gene; genotypes were divided into three groups (AA; AK; KK); alleles V and L of the GH gene; genotypes were divided into three groups (VV; VL; LL); alleles A and B of the PRL gene; genotypes were divided into three groups (AA; AB; BB). Data on milk production for 1st and 3rd lactation of cows with different genotypes CSN3; DGAT1; GH; PRL were used for the study. One-way analysis of variance was carried out using the Excel software application from the Microsoft Office package; according to which the influence of the polymorphism factor of the studied genes on the indicators of milk production of cows was determined.

According to the prolactin gene; a significant proportion of the influence is observed in cows in the 3rd lactation in terms of the mass fraction of fat in milk ?2= 0.044 (F= 3.822; P<0.05) (table 4). No significant and reliable influence was found in terms of other indicators (Table 3).

Thus; it was revealed that the kappa-casein gene had the greatest influence on the mass fraction of protein; diacylglycerol O-acyltransferase and prolactin on the mass fraction of fat; somatotropin on milk yield. An analysis of variance was also carried out for the influence of individual alleles of marker genes on the indicators of milk production of cows. It was found that allele A of the kappa-casein gene has a significant effect on the qualitative indicators of milk production of cows: milk fat ?2= 0.035 (F= 4.727; P<0.05); the mass fraction of protein in milk ?2= 0.036 (F= 4.879; P<0.05); milk protein ?2= 0.032 (F= 4.365; P<0.05); provided that protein content of milk had the highest proportion of influence. Allele B of the kappa-casein gene has a significant effect only on the mass fraction of protein ?2= 0.342 with a high value of Fisher's criterion that is Ffactual= 26.489 (P<0.001). This suggests that both the genotype and the allele of kappa-casein are closely related to the high protein content of milk of animals. Consequently; the protein content of milk of cows is 34-35% dependent on the kappa-casein gene and its allelic variant. The degree of influence of the desired B allele on other indicators of milk production was less than ?2= 0.013 Allele A of the diacylglycerol O-acyltransferase gene had the greatest effect on the amount of milk fat that was ?2= 0.058 (F= 7.949; P<0.01). It also had a significant effect on milk yield ?2= 0.045 (F= 6.175; P<0.05) and the milkness index ?2= 0.056 (F= 7.743; P<0.01); which was not observed for allele A of the kappa-casein gene. The desired allele K of the diacylglycerol O-acyltransferase gene had the greatest significant influence on the fat mass fraction in the milk of first-calf heifers; its influence was ?2= 0.163 (F= 17.305; P<0.001). Also; the significant influence of this allele was in terms of the mass fraction of protein in milk ?2= 0.061 (F= 5.739; P<0.05) and according to the milkness index ?2= 0.051 (F= 4.794; P<0.05). Consequently; it also will be possible to achieve an increase in protein content of milk with a targeted fat content of milk. The allele V of the somatotropin gene has a significant effect only on the yield of milk protein ?2= 0.097 with the value of Fisher's criterion that is Ffactual= 3.641 (P<0.05). For alleles A and B of the prolactin gene; no reliable and significant influences on the indicators of milk production of cows were revealed (Table 4).

The genotype and allele B of kappa-casein has the strongest and most reliable effect on protein content of milk; the genotype and allele K of diacylglycerol O-acyltransferase and also prolactin genotype on fat content of milk; Somatotropin genotype on the level of milk yield. At the same time; among the studied marker genes the CSN3 and DGAT1 genes have a wider influence on the indicators of milk production.

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