Estimation of inbreeding values using genomic run of homozygosity and study of evolutionary trend for effective population size in some Asian horse breeds

The objective of the present study was to estimate the inbreeding values using run of homozygosity and study the evolutionary trend of the effective population size (Ne) in some Asian horse breeds. A total of 99 animal samples consisting 19, 24, 18, 19 and 19 samples from AkhalTake, Arrabian, Caspian, Mongolian and Thoroughbred breeds, genotyped by Illumina SNP50K Beadchip assay were used in this study, respectively. This study has been performed in collaboration with the Equine Genetic Diversity Consortium (EGDC) project. The inbreeding values based on the run of homozygosity using FROH and next, Ne using linkage disequilibrium across 5 up to 1000 generations ago were estimated. The result of principal component analysis (PCA) indicated that all breeds will be separated from each other in the first two principal components. Average expected and observed heterozygosity for different breeds ranged 0.278-0.294 and 0.278-0.308 respectively. Estimation of inbreeding based on genomic information showed that the values are ranged between 0.003 in Mongolian up to 0.166 in Thoroughbreds. The Ne results showed a decreasing trend over the last 1000 generations for all breeds, with an increasing slope since about 100 generations ago. The highest historically effective population size in recent generations (5 generations ago) was found in the Arabian breed (53 heads) and the lowest for Caspian and Thoroughbred (33-34 heads) breeds. Generally, the results of this study indicated that despite a reasonable genetic variation and low inbreeding value, however, the Ne is the lowest in Caspian compared to other Asian horse breeds that designing of appropriate programs is necessary to conserve remaining purebred animals of this indigenous Iranian horse breed.