Gait keeper gene no magic bullet for cold-blooded trotters in Sweden and Norway – study

 Coldblood Trotter of mixed Swedish and Norwegian lines. Photo: Don Wright CC BY 2.0 via Wikimedia Commons
A Coldblooded Trotter of mixed Swedish and Norwegian lines. Photo: Don Wright CC BY 2.0 via Wikimedia Commons

The so-called gait keeper gene does not appear to be the Holy Grail for track performance in the cold-blooded trotters that race in Sweden and Norway, the findings of a study suggest.

Researchers from the Swedish University of Agricultural Sciences set out to learn more about the influence of the so-called gait keeper mutation in the DMRT3 gene on Swedish-Norwegian Coldblooded Trotters used in harness racing in the region.

Studies have shown that a particular mutation in the gene − a change from cytosine (C) to adenine (A) − affects trotting gaits and also has a major impact on harness racing performance in several breeds. Scientists dubbed it the gait keeper gene because of these effects.

In Standardbreds, the DMRT3 mutation has been shown to be of great importance for the ability to trot at high speed, with most Standardbreds being homozygous for the mutation – that is, inheriting a copy of the mutated gene from both parents (AA).

Doctoral researcher Kim Jäderkvist Fegraeus and her colleagues, writing in the open-access peer-reviewed journal PLOS ONE, said that although Standardbreds and Coldblooded Trotters were bred and selected for the same purpose, the frequency of the DMRT3 mutation was much lower in the local breed.

Not only that, but the effect of the mutation was not as obvious in Coldblooded Trotters.

In a previously reported study, Coldblooded Trotters that carried a copy of the mutated gene from each parent (AA) were found to be more successful at three years of age on the basis of prize money earned, but as the horses matured the association weakened.

In contrast, studies of both Standardbreds and Finnhorses (a Finnish Coldblooded Trotter), clearly showed the superiority of AA horses for all traits regardless of age.

The study team said assessing the influence of the gait keeper gene on Coldblooded Trotters was important, given its potential for significantly altering the genomic architecture of the breed.

“While not as extreme amongst Coldblooded Trotter breeders compared to Thoroughbreds or Standardbreds, the desire for a quick return on a horse is common across all racing breeds,” they said.

“The nature of the industry, be it gallop or harness racing, tends to favor precocious horses that can not only start competing, but also win, at a young age.”

The possible association between a single gene and good early race performance could easily push the selection of the breed in one direction, reducing the genetic variation of an already limited population.

The researchers set out to investigate the suggested precociousness of Coldblooded Trotters that inherited a copy of the mutated gene from both parents, as well as the association between the DMRT3 mutation and racing performance at older ages.

A total of 769 randomly selected Coldblooded Trotters were used in the study – 485 raced and 284 unraced.

All were tested for the DMRT3 mutation.

The association of the mutation with racing performance was investigated for 13 performance traits across three different age intervals – 3 years, 3 to 6 years, and 7 to 10 years – using statistical software. The traits centered around rankings, racing times, earnings, disqualifications, and breeding values.

The results suggested no association of the DMRT3 mutation with precocity – that is, performance at three years of age.

Only two traits – race time and the number of disqualifications – were found to be significantly different between the genotypes, with AA horses having the fastest times and horses without the mutation having the highest number of disqualifications at 3 years of age.

The frequency of the AA genotype was much lower in the raced group of horses compared with the unraced sample, and less than 50% of the horses that inherited the mutated gene from both parents participated in a race.

For the age intervals 3 to 6 and 7 to 10 years the horses that carried both copies of the gene (AA) also failed to demonstrate significantly better performance than the other genotypes.

Inheriting the mutated gait keeper gene from both parents did not not appear to be associated with superior performance, early or late, in the racing career of Swedish-Norwegian Coldblooded Trotters, the study team reported, despite it being suggested as the most favorable genotype for racing performance in Standardbreds and Finnhorses across all ages.

Discussing their findings, the researchers said: “Although a previous study indicated a favorable association between the AA genotype for DMRT3 and superior performance in young Coldblooded Trotters, the current study provides no evidence to support such an association.”

The lack of concordance between the studies may be due to the larger, randomly selected pool of horses used in the latest research.

The authors acknowledged two significant differences between the two genotypes, in race time under the voltstart starting method and number of disqualifications.

However, the proportion of AA horses that raced for the first time at three years of age and the average age for the first race did not differ significantly from the other genotypes.

“If AA horses were truly more precocious, a clear difference would be apparent, with a greater proportion of AA horses racing at three years of age.

The fact that most of the Coldblooded Trotters in the study were heterozygous for the DMRT3 mutation − that is, they inherited a copy from only one parent − strongly suggested no significant association between DMRT3 and precocity, they said.

The authors continued: “Perhaps a more interesting observation is the rather low proportion of raced AA horses.

“As the ability to race is the most important factor for a successful racehorse, the large proportion of unraced AA horses suggests a possible unfavorable association of the genotype with racing performance.

“The AA horses that made it to the racetrack performed well up to six years of age, as indicated by high median values for earnings and victories.

“Although successful at young ages, the AA horses did not perform as well for the older ages, where the median values for earnings and victories were the lowest of the three genotypes.”

It was also worth noting that the AA horses had the lowest number of starts for all ages except at three years of age.

They concluded that the DMRT3 mutation did not appear to influence precocity in Coldblooded Trotters. “However, the current study suggests an association of DMRT3 genotype and the ability to start racing.

“As the effect of the DMRT3 mutation in Coldblooded Trotters appears to be disparate from the effect seen in other harness racing breeds, additional studies on Coldblooded Trotters would be beneficial to fully understand the influence of the gene on harness racing performance.”

The study team comprised Fegraeus, Chameli Lawrence, Katrine Petäjistö, Maria Johansson, Maja Wiklund, Christina Olsson, Leif Andersson, Lisa Andersson, Knut Røed, Carl-Fredrik Ihler, Eric Strand, Gabriella Lindgren, and Brandon Velie.

Jäderkvist Fegraeus K, Lawrence C, Petäjistö K, Johansson MK, Wiklund M, Olsson C, et al. (2017) Lack of significant associations with early career performance suggest no link between the DMRT3 “Gait Keeper” mutation and precocity in Coldblooded trotters. PLoS ONE 12(5): e0177351. https://doi.org/10.1371/journal.pone.0177351

The study, published under a Creative Commons License, can be read here

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