Polymorphism in myostatin gene and athletic performance in Nordic horse breeds
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- Master's theses (IHA) 
Athletic performance including working ability, riding, racing and endurance has played a leading role in horse breeding possibly since their domestication. Even though traits of athletic performance are considered as complex and dependant on environment, management and training, it has been shown that heritability of some performance traits can be considerably high. Skeletal muscle system seems to be a key factor to exceptional athletic performance and numerous studies in other species (dogs, humans, sheep, cattle etc.) have shown that polymorphisms in MSTN gene can be responsible for phenotypic changes in muscle tissues. Several studies focusing on horse MSTN gene region have been made and some significant associations discovered in Thoroughbred populations. The main objective of this study is to estimate the allele frequencies of the g.66493737 SNP, which is the strongest associated SNP with the optimim race distance, and some additional SNPs (two in a promoter region and one downstream the gene) in MSTN gene of Nordic horse breeds and correlate them with performance trait data to create a deeper understanding of the gene’s influence on performance ability in horses. For analysis 25 horse breeds and four Donkey and Przewalski’s horse individuals were selected. Four SNP marker positions (g.65868604G>T, g.66493737C>T, g.66495696G>A, g.66495826G>A) and one insertion (Ins227) were chosen based on previously published research results. For genotyping SNPs real time PCR TaqMan approach and touchdown PCR for detection of Ins227 was used. Phenotypic data of performance traits were correlated with inferred haplotypes of Icelandic Horse and Coldblooded Trotters using R software. Results revealed segregation in all SNP marker positions, having variable allele frequencies between breeds and lacking g.66495696G homozygous individuals. No Ins227 allele was detected, except those in Thoroughbred horses and one heterozygous individual of Swedish Warmblood. Haplotype association resulted in some significant haplotype effects on proportions (p-value<0.05) and tolt - running walk - ability (p-value<0.05) in Icelandic horse. More significant effect was detected for Coldblooded Trotters where both haplotypes having mutation in proximal promoter region had a significant effect on total BLUP value and BLUP values for Position, Earnings and Time. Haplotype having g.66495696G allele shoved the most significant association having p-values from 0.029 for Start status BLUP value to 0.001 for Position and Earnings. Finally, we can conclude that tested polymorphisms in MSTN gene are widespread in Nordic Horse breeds and there are indications that some of them might have a functional effect on horse performance traits. In addition, we have obtained specific directions of further research possibilities.