Relationship of polymorphic prolactin genes and growth hormones in dairy cattle
The article reports the study findings on polymorphism of the prolactin (PRL) and somatotropin (GH) genes in connection with the dairy productivity of black-and-white and Bestuzhev cattle breeds. The PCR-RFLP method was used to reveal the gene polymorphism. The study established allele frequencies in the genes. The study also revealed a broad tendency for the relationship of milk productivity in both the black-and-white and Bestuzhev breeds with their PRL and GH genotypes. The genotype identity suggests that the homozygotic cows with the PRL<sup>aa</sup> genotypes feature lower milk productivity compared to the cows with other genotypes (PRL<sup>bb</sup> and PRL<sup>ab</sup>). The described ratio was true for both milk yields and milk fat. The fat mass fraction was greater in the milk of cows with the genotype PRL<sup>aa</sup> compared to the genotype PRL<sup>ab</sup> and PRL<sup>bb</sup>. The study showed that the alleles of GH<sup>V</sup>AluIpolymorphic site, GH<sup>D</sup>MspI polymorphic site of the growth hormone (GH) gene, and the PRL<sup>b</sup> prolactin gene in the cattle were productive in terms of economic value. Complex genotypes with several genes at the same time were identified. These genotypes can increase the level of milk productivity. The following genotypes demonstrated a positive effect on milk yields in the two breeds: GH<sup>lv(vv)</sup>GH<sup>cd</sup>PRL<sup>ab</sup> and GH<sup>lv</sup>GH<sup>dd(cd)</sup>PRL<sup>bb</sup>. The relationship of the complex genotypes based on the PRL and GH genes with milk productivity indices was also determined. The study identified complex genotypes associated with both higher (above average) and lower (below average) productivity indices in the two breeds. The findings can be helpful in breeding practices as they may foster the gene pool formation of the planned cattle breeds with the specific gene combinations.