The high level of diversity of the genetic structure of mitochondrial DNA and inheritance through the maternal line make it a unique object for studying evolutionary processes, phylogenetic relationships and assessing population diversity. 64 thoroughbred horse mares were selected from 20 main dam families and the most promising branches for analysis of the non-coding region of the mtDNA D-loop. Primers for amplification of the mtDNA D-loop region were selected taking into account the reference sequence of the fossil Swedish horse X79547. GeneBank data was used for 17 haplogroups located under the access number (n = 83): JN398377-JN398457, EF597513-EF597514 for identifying the obtained nucleotide sequences. The 530 mtDNA D-loop region analysis was performed using the MEGA4 program. 23 haplotypes corresponding to 8 haplogroups A, B, G, H, I, L, M and N according to the classification of Achilli et al. (2012) were identified in the process of studying the polymorphism of the hypervariable region of the mtDNA D-loop in dam families of thoroughbred horse breed. Among mares from 20 dam families 16 were identified as belonging to only one haplogroup. 2 haplogroups were identified in 4 dam families of this breed (4,5,9, 19) due mainly to transitions at different breeding periods of thoroughbred riding horses. The genetic analysis of the mitochondrial genome of the main dam lines of thoroughbred horse breed indicates a rather high level of diversity of mtDNA haplotypes and a clear differentiation of female families in the domestic population of this breed..
Purpose: to study the effect of the level of homozygosity and inbreeding on the fecundity of thoroughbred mares.Materials and methods. A total of 3662 heads of breeding sows from leading stud farms of the Russian Federation were selected for the analysis. The influence of the homozygosity level on 17 microsatellite DNA loci on the main indices of reproduction of thoroughbred mares, such as the safe yield of foals and the number of fetal years, was analyzed in the article. All mares in the experimental sample had at least three years of breeding use. Individual fecundity rates and the number of homozygous loci in the STR profile were calculated for each horse.Results. The highest live foal yields (75.92%) had sows with homozygosity levels of 62.78-69.02%, and the lowest foal yields (45.73%) were recorded in mares with the highest homozygosity levels (75.28-76.92%). The maximum foal yield (65.85%) was determined in sows with an inbreeding rate of 4.1% or more, with a productive longevity of 6.26 fetal years on average. Analysis of the data showed that the level of inbreeding had almost no effect on the yield of live foals (R=0.010 at P>0.05), but had a negative correlation with the number of fruiting years (R=-0.092 at P<0.005).Conclusion. Estimation of homozygosity level of thoroughbred horses is especially relevant, as this breed has been perfected by purebred breeding method only for more than thirty years. In the thoroughbred horse breed, it is necessary to create a system of maintaining heterozygosity as well as the diversity of genotypes through the organization of breeding work.
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