Association of SNP localized near DIO2 gene with hormonal profiles of the thyroid axis and fertility indicators in black-and-white cows

Thyroid hormones can affect the reproductive function of cows through the regulation of various metabolic pathways. The activity of the thyroid system is under the control of three types of deiodinases (DIO). In cattle, there are several genetic variants for the DIO1 and DIO3 genes, but there is no information on the polymorphism of the DIO2 gene. Purpose: to conduct a search for genetic variants for SNPs in the DIO2 gene and in nearby regions and investigate their association with prepartum and postpartum thyroid profiles and reproductive performance in dairy cows. Materials and methods. Black-and-white cows of calving 2-4 were used in the experiments. Before calving and after calving, blood was taken from the animals to determine the concentration of hormones by ELISA. The assessment of the luteal activity of the ovaries was performed on the basis of an ultrasound study and the content of progesterone in the blood. Genotyping was performed on 48 samples of cow DNA using a Bovine GGP 150K biochip. Results. No SNPs present on the Bovine GGP 150K chip were found within the target gene. The SNP Bovine- HD1000026761, localized upstream of the DIO2 gene, was selected for research, with a frequency of genotypes being 45.83% (AA), 47.92% (AG), and 6.25% (GG). In cows with the AA and AG genotypes, a decrease of 1.4 times (p<0.01) in the blood concentration of total thyroxine (T4) 2 weeks before calving, compared with that for 4 weeks, and its further decrease by 1.5 -1.9 times (p<0.001-p<0.05) by the 1st week of lactation were found. From the 6th to the 2nd week before parturition, this indicator was 1.5–1.6 times higher (p<0.001–p<0.05) in individuals with the AG genotype than in ones with the AA genotype. In animals with the AG genotype, a decrease in the blood concentration of reverse T3 (1.4 times, p<0.05) between the 4th week before calving and the 1st week of lactation was revealed. At the same time, this concentration was relatively constant in the animals of the other two groups. Furthermore, in animals with the AG genotype, the content of rT3 in the blood was 1.3 times lower than in animals with the AA genotype from the 3rd to the 7th week of lactation. In cows with a heterozygous genotype, the T4/T3 ratio increased 2.1 times (p<0.001) between the 2nd week before calving and the 1st week after calving, and then decreased 2.2 times (p<0.001) to the 3rd week. After 1 week of lactation, this ratio was 1.9 times higher (p<0.001) than in animals with the AA genotype. Meanwhile, the frequency of occurrence of individuals with the shortest period of recovery of the ovarian function and open days period was the lowest in the group with the AA genotype. Conclusions. The data obtained indicate that the SNP BovineHD1000026761, located upstream of the DIO2 gene, is associated with long-term changes in thyroid hormone levels in the prepartum and postpartum periods.