Abstract
The Swedish‐Norwegian Coldblooded trotter and the heavier North‐Swedish draught horse both descend from the North‐Swedish horse, but the Coldblooded trotters have been selected for racing performance while the North‐Swedish draught horse is mainly used for agricultural and forestry work. By comparing the genomes of Coldblooded trotters, North‐Swedish draught horses and Standardbreds for a large number of single‐nucleotide polymorphisms (SNPs), the aim of the study was to identify genetic regions that may be under selection for racing performance. We hypothesized that the selection for racing performance, in combination with unauthorized crossbreeding of Coldblooded trotters and Standardbreds, has created regions in the genome where the Coldblooded trotters and Standardbreds are similar, but differ from the North‐Swedish draught horse. A fixation index (Fst) analysis was performed and sliding window Delta Fst values were calculated across the three breeds. Five windows, where the average Fst between Coldblooded trotters and Standardbreds was low and the average Fst between Coldblooded trotters and North‐Swedish draught horses was high, were selected for further investigation. Associations between the most highly ranked SNPs and harness racing performance were analyzed in 400 raced Coldblooded trotters with race records. One SNP showed a significant association with racing performance, with the CC genotype appearing to be negatively associated. The SNP identified was genotyped in 1915 horses of 18 different breeds. The frequency of the TT genotype was high in breeds typically used for racing and show jumping while the frequency of the CC genotype was high in most pony breeds and draught horses. The closest gene in this region was the Endothelin3 gene (EDN3), a gene mainly involved in melanocyte and enteric neuron development. Both functional genetic and physiological studies are needed to fully understand the possible impacts of the gene on racing performance.
Highlights
Descending from the North-Swedish horse, the Coldblooded trotter is a unique racehorse breed with a draught horse origin
Based on 37,246 single-nucleotide polymorphisms (SNPs) the average Fst values between the three breeds included in the Delta Fst analysis were: 0.082 (Coldblooded trotters vs. Standardbreds), 0.041 (Coldblooded trotters vs. North-Swedish draught horses) and 0.088 (North-Swedish draught horses vs. Standardbreds)
If two closely located windows had a similar Delta Fst value, only the window with the highest Delta Fst value was selected, as the SNPs were likely to be in linkage disequilibrium (LD)
Summary
Descending from the North-Swedish horse, the Coldblooded trotter is a unique racehorse breed with a draught horse origin. Horse racing has fascinated humans for hundreds of years and many of the North-Swedish horses were used for work and for racing. The first official harness race with North-Swedish horses took place already in the early 1800s. When interest in harness racing grew breeders began to select for faster and more sustainable horses. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society.
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