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The athletic nature of the horse and the large number of diverse horse breeds provides an opportunity to study the genetics of locomotion pattern and performance in mammals. The overall aim of this thesis was to get a better understanding of the genetics behind gaits and performance in the horse. This thesis compiles four papers on four different horse breeds. In studies I and II we describe the effect of a known mutation in the doublesex and mab-3 related transcription factor3 (DMRT3) gene on harness racing performance in Swedish-Norwegian Coldblooded trotters and Finnhorses. Previous studies have demonstrated a major impact of the gene on harness racing performance results in Standardbreds. While the gene clearly is important for harness racing performance in both Coldblooded trotters and Finnhorses, the most successful genotype differed between the two breeds. The homozygous mutant (AA) Finnhorses were most successful on the racetrack but had difficulties in performing a good canter in riding. For Coldblooded trotters the CA horses were the better race horses overall, even though the AA horses performed well at young ages. While previous studies have reported that homozygozity for the DMRT3 mutation (AA) is required for a horse to be able to pace, not all AA horses can pace. To understand more about the genetic regulation of pace, in study III we compared the genomes of AA Icelandic horses with and without the ability to pace. We performed a genome-wide association study and identified a potential candidate region that contained a gene known to influence memory and learning ability. In study IV we utilized the close relationship between the Coldblooded trotter and the North-Swedish draught horse to identify novel genes influencing harness racing performance. The two breeds are genetically similar but have been selected for different traits. By comparing the genomes of the two breeds with the genome of Standardbreds, we identified five top regions where the Coldblooded trotters and Standardbreds were similar but together differed from the North-Swedish draught horse. One of the regions identified contained five single nucleotide polymorphisms (SNPs) that were significantly associated with racing performance in Coldblooded trotters. In conclusion, this research shows that carefully selected horse materials can serve as models to gain deeper knowledge on the genetics of performance and locomotion pattern. It is also vital to contextualize the importance of these genes within each horse breed. |
