The genetic signature of Swedish Warmblood horses points to a strong preference among breeders for performance, according to researchers.
The genes show that breeders are chasing desirable behaviour, physical abilities and fertility.
The Swedish Warmblood is selected for equestrian sport, mainly showjumping and dressage.
Its origin dates back to the 18th century when the Royal Cavalry requested more agile and faster horses, leading to intensified breeding and selection of Swedish riding horses.
The Swedish Warmblood studbook was founded in 1928 with the initial aim to breed horses for multiple equestrian purposes.
Since the demand for physical and mental abilities in sport horses has increased noticeably in recent decades, selection of Swedish Warmbloods for specific disciplines — dressage or show-jumping — is now common practice.
The current goal is to breed internationally competitive warmbloods in terms of rideability, performance-oriented temperament, excellent gaits and/or jumping ability.
Researchers from the Swedish University of Agricultural Sciences set out in their study to identify the genomic regions under selection in the breed.
They genotyped 380 Swedish Warmbloods and, for comparison, 274 Exmoor ponies, a breed for which the Exmoor Pony Society primarily aims to preserve its genetic diversity. Therefore, selection for sport performance traits is not practiced.
The genomic scan for homozygous regions identified long runs of homozygosity shared by more than 85% of the genotyped Swedish Warmbloods used in the study. These runs were located on ECA4, ECA6, ECA7, ECA10 and ECA17.
Runs of homozygosity are continuous lengths of DNA in which both parents have supplied identical genetic material.
In the Exmoor ponies, long runs of homozygosity were instead distributed evenly across the genome of Exmoor ponies in 77% of the chromosomes.
The results, reported in the journal BMC Genomics, indicate that genes related to behaviour, physical abilities and fertility appear to be targets of selection in Swedish warmbloods. Selection was evident in regions containing genes primarily involved in nervous system functionality, as well as muscle contraction and development.
Discussing their findings, the authors said the overlapping homozygous segments shared in most of the warmblood horses agree with the intensified selective breeding program applied in the past 40 years.
“We believe this is an indication that shared homozygous segments in Swedish Warmblood horses can be a result of recent selection for performance, rather than inbreeding.”
This, they said, was supported by the estimated inbreeding coefficient being below 5% in all but six of the warmbloods used in the study. It is likely to be a result of a semi-open studbook allowing inflow of genetic material from other warmblood populations, they added.
“In contrast, runs of homozygosity of all lengths were evenly spread across the genome of Exmoor ponies.” Short runs were up to five times more frequent in Exmoor ponies.
They said the long runs seen in the Exmoor ponies may be the result of past breeding bottlenecks, given the breed’s endangered status.
The full study team comprised Åsa Viklund, Gabriella Lindgren, Susanne Eriksson and Sofia Mikko, all with the Swedish University of Agricultural Sciences; and Michela Ablondi, with the University of Parma in Italy.
Signatures of selection in the genome of Swedish warmblood horses selected for sport performance
Michela Ablondi, Åsa Viklund, Gabriella Lindgren, Susanne Eriksson and Sofia Mikko
BMC Genomics volume 20, Article number: 717 (2019) https://doi.org/10.1186/s12864-019-6079-1