Epsilon Archive for Student Projects

Abstract

This study investigated the association of single-nucleotide polymorphisms (SNPs) of three
different genes with pace racing performance in the Icelandic horse. The SNPs chosen were
PR3737, PR8604 and PR9482 of the Myostatin gene; SNPs g.41206762 C>T and g.41218272
T>C of the GRIN2B gene and SNP g.22496787 T>C of the DOCK8 gene. Icelandic horses that
compete frequently in any of the three pace race disciplines (P1 over 250m, P2 over 100m and
P3 over 150m) were genotyped for all SNPs mentioned above. The horses in the sample
(n=131) were divided into “Speed groups” based on consistency of racing times and training
schemes. Three groups were created: Fast (n=37), Average (n=75) and Slow (n=19).

Differences in genotype distribution among the different Speed groups were evaluated using
Fisher’s Exact Test. Significant differences were found for all SNPs except PR9482 when
comparing only Fast versus Slow horses. Significant differences were also found between all
three groups when comparing allele frequencies. Moreover, a drastic difference in allele
frequency of the mutant allele for the DOCK8 SNP was found between horses of the Fast group
(frequency of the mutant allele was of 0.70) and 280 Icelandic horses genotyped for other
studies (mutant allele frequency ranging between 0.33 (n=95) and 0.43 (n=192)). This implies
an important role of this SNP and its mutant allele in pace-racing performance. Additionally,
horses were evaluated by owners in terms of three temperament traits: Nervousness, Focus and
Motivation. Significant differences were found in the distribution of scores for these
temperament traits between horses with the different genotypes of the GRIN2B SNPs,
suggesting a beneficial effect of the mutant alleles on the horse’s temperament.

An association analysis was also performed, where the genotypes were evaluated for
association with life-time racing performance results for race times (P1, P2 and/or P3),
Breeding Field Test (BFT) assessment scores for pace and estimated breeding values (EBV)
for pace at BFTs. Additionally, the genotypes were evaluated for association with performance
results obtained when the horses competed at the age of 13 years or under (n=117) and over 13
years of age (n=64). Significant associations were found for PR9482, where the C allele
(stamina-related in other breeds) was beneficial to performance in the longer P1 races and the
T allele (speed-related in other breeds) was beneficial to performance in P3 for horses of ages
13 and under. Associations were also found for the GRIN2B SNP, with the C (mutant) allele
having a beneficial effect in the shorter P3 races for both lifetime career and performance in
the age group of 13 years and under. As for DOCK8, associations were also found in relation
to P2, with the mutant (T) allele having a positive effect on the performance. No associations
were found with any of the studied polymorphisms with BFT assessment scores for pace or
with estimated breeding values.

This study concludes that a SNP at the DOCK8 gene may well be beneficial to performance in
pace-racing Icelandic horses due to the associations found with racing times and, more
interestingly, the difference found in mutant allele frequencies between an elite group of racers
and the rest of the population. Additionally, the study showcases the importance of
temperament traits as factors that affect performance in pace-racing, as evidenced by the
associations found between the mutant allele of the GRIN2B polymorphism and temperament
scores, along with racing times. Furthermore, the study concludes that Myostatin SNPs have
little effect in pace-racing performance, seeing as only one polymorphism affected
performance and only in one of the age groups. Moreover, comparing mutant allele frequencies
between the elite racers and a large number of Icelandic horses that were not selected for pace
racing showed no variation at all. This further indicates these mutations may not play a major
role in performance as they do in other breeds, such as the Thoroughbreds.