Does heterozygosity at the DMRT3 gene make French trotters better racers?

This research investigates whether a specific gene (DMRT3) variation influences the racing performance of French trotter horses and why these gene variants still exist. The study found that the mixed gene variant increased earnings in horses aged 5 years or older, suggesting a beneficial effect in mature racehorses.

Research Context

• The research is based on a mutation identified in the DMRT3 gene, which is associated with horses’ pacing ability.
• The mutated allele, referred to as “A,” is dominant in the American Standardbred trotter breed, whereas the original or “wild” allele “C” maintains a 24% presence in French trotter breeds.
• The main objective of the study was to understand whether the DMRT3 genetic variations impact the performance of French trotter horses and to comprehend why allele C is still prevalent in this breed.

Methodology

• The researchers utilized a mixed animal model and extracted data from 173,176 French trotter race outcomes to calculate genetic parameters and the environmental effects on performance traits.
• The effect of the DMRT3 gene was determined by evaluating the impact of the closely linked SNP (Single Nucleotide Polymorphism) BIEC2-620109.
• A selection scheme was devised that incorporated both qualification and racing performance. The purpose was (1) to check if the better performance of horses with a mixture of C and T alleles at the SNP could be explained solely by selection, and (2) to understand why the C allele has not disappeared in French trotters.

Results

• The heritability of racing performance traits ranged from high for qualification test (0.56), average for annual earnings per completed race (0.26 to 0.31), and low for proportion of disqualified races (0.06 to 0.09).
• The CC genotype was consistently less favorable compared to the TT genotype for qualification. The probability to qualify was 20% for CC genotype horses vs. 48% for TT genotype, and earnings were also significantly lower for horses with the CC genotype.
• Interestingly, the CT genotype, although unfavorable for qualification (40%) and earnings at age 3 (-0.21 σy), was beneficial for earnings in horses older than 5 years (up by 0.41 σy). This indicates a positive impact on the performance of older horses and suggests why this variant might still exist in the breed.
• Selection based on qualification performance could explain only up to 19% of the earnings difference seen between CC and CT genotypes in horses older than 5 years.

Conclusions

• The study concluded that the use of mature horses in the French racing circuit could explain why the CT genotype is still evident in French trotters. This seems to imply that the gene variant brings a competitive advantage in more mature horses.