The so-called gait-keeper gene only partially explains the unique gaits of the Colombian paso horse, according to researchers.
They have concluded that other modifying genes likely influence these special gaits.
The Colombian paso horse breed, also known as Colombian criollo paso horse, is the most important horse breed in Colombia, with more than 220,000 animals registered in the studbook.
The breed is likely derived from a mix of Spanish horses brought by the conquerors to America starting in 1493.
This group of horses included the Spanish Jennet horse, which was known to perform ambling gaits.
At the start of the 20th century, the Colombian paso horse consisted of a mix of horses that performed several different stepping gaits.
The breed has been intensively selected for their gaits – the paso fino, trocha and trot – since 1980.
Currently, the breed is divided into four groups which have generally not been crossed in the last 30 years. The groupings, as their names suggest, are based on their gaits: the Colombian paso fino group; the Colombian trocha group; the Colombian trocha and gallop group; and the Colombian trot and gallop group.
There are three breed-specific gaits within the Colombian paso horse breed: the paso fino, trocha, and Colombian trot. These gaits are highly collected with a high stride frequency.
All the gaits of these horses exhibit a high animation and energy expenditure.
The four-beat paso fino gait is performed only by the Colombian paso fino group. There are some gaits in other horse breeds, with the same footfall pattern to paso fino, for example, the tölt in Icelandic horses, the marcha picada in Mangalarga-marchador, the paso fino in Puerto Rican paso fino horses, and the peruvian paso gait in Peruvian paso horses.
The four-beat trocha gait is performed only by the Colombian trocha and Colombian trocha and gallop groups. Other gaits with a similar footfall pattern are the foxtrot in the Missouri Foxtrotter and the marcha batida in the Mangalarga-marchador breed.
The trot gait is performed by the Colombian trot and gallop group and can be considered a variant of the regular trot. It is a two-beat diagonally coupled gait which is highly collected. In competitions, horses in these groups are judged for their gallop, which is a variant of the traditional canter. This asymmetric gait is a highly collected canter.
Miguel Novoa-Bravo and his colleagues, writing in the open-access journal PLOS ONE, said the ability to perform alternative gaits is partly due to genetics.
In 2012, the DMRT3 “gait-keeper” gene mutation was singled out as being associated with gait performance and harness racing performance in several gaited and harness racing horse breeds.
The authors noted that the genotype frequencies for the nonsense mutation that gave rise to the DMRT3 gene had been found to differ between the four Colombian paso horse groups in a previous study.
They hypothesized that the selection on the gaits performed by the Colombian paso horse breed has led to body motion differences that can be explained, at least partly, by the nonsense mutation in the DMRT3 gene.
They set out to identify if there were any differences in movement variables and genetic variants between the Colombian paso horse’s gaits. They also sought to evaluate if and how much the gait differences were explained by the nonsense mutation in the DMRT3 gene.
The research centered on 187 Colombian paso horses, comprising 99 males and 88 females, evenly distributed among the four groups. They were selected based on their participation in Fedequinas national competitions and their performed gait.
A visual examination using slow motion videos was performed to confirm the gait classification of the horses. Kinematic measurements for 172 of the 187 horses were taken and their genealogy was explored.
Hair samples from 152 of the horses underwent genetic analysis, including testing for the gait-keeper gene.
“The results indicated that there are significant kinematic and DMRT3 differences between the Colombian paso horse’s gaits, and those parameters can be used partially to select and control the horse’s gait performance,” they reported.
“However, the DMRT3 gene does not play a major role in controlling the trocha and the Colombian trot gaits. Therefore, modifying genes likely influence these gaits.”
Discussing their findings, the authors said paso fino, trocha, and Colombian trot performed by Colombian paso horses were distinctive for this breed.
“For all the gaits, there is always at least one limb in stance phase and there is a high stride frequency and short stride length.
“The stride frequencies for the paso fino (2.60–2.85 strides per second) and trocha gait (2.70–2.96 strides per second) are higher than for similar walking gaits as tölt and foxtrot (2.23–2.36 strides per second), and comparable to the stride frequency at gallop in racing breeds like the Thoroughbred (2.27–2.92 strides per second).
“On the other hand, the stride length of the Colombian paso horse gaits is shorter (0.64–0.85 m) than in other walking gaits like tölt and foxtrot.”
They continued: “These characteristics make it difficult to distinguish the Colombian paso horse gaits by just using just the human eye, and even more difficult to evaluate the footfall pattern and the kinematic parameters of the gaits.”
They found the mutant A-allele of the DMRT3 gene was significantly associated with the horses’ ability to perform the paso fino gait, whereas it seemed that the AA genotype was required for a horse to perform this gait.
“In our sample, the mutation was fixed in the Colombian paso fino group and it was found in low frequencies in the other horse groups.”
The high frequency of the mutation in the Colombian paso fino group could be explained by a high artificial selection pressure in this group, considering that they are separated from the trocha and trot horses in competitions, and breeders have been selecting horses with a clear paso fino gait.
“On the other hand, it seems to be a selection against the DMRT3 AA genotype in horses performing the trocha and Colombian trot.
Selection for the trocha gait appears to favor the CC genotype, indicating that DMRT3 is likely not the most important gene responsible for controlling the lateral footfall pattern in this gait.
The ambivalent position of the trocha gait is interesting, the researchers say.
“Based on the kinematic measurements, the trocha gait is closer to the paso fino gait than to the trot gait, and the trocha gait is not explained by the DMRT3 mutant A-allele as it is for the paso fino gait.”
The authors propose two options to explain the nature of the trocha gait.
“The first hypothesis is that the trocha gait is an artificial gait (not inherited but conditioned by training) and could be considered as a dissociation from trot. The second hypothesis is that the trocha gait is a natural gait (inherited), and that there are other genes that explain this gait.”
The researchers said their findings supports the hypothesis that selection within the breed groups has produced kinematic differences between the Colombian paso horse’s gaits, particularly between the Colombian trot and the other gaits (the paso fino and trocha gait).
“The DMRT3 mutation seems to explain the horses’ ability to perform the paso fino gait but not the other diagonal coupled gaits (trocha and Colombian trot).
“However, there were no microsatellite or DMRT3 genotype differences between horses performing the trocha and the Colombian trot gait.
“We propose that trocha is an inherited gait and its ambivalent position could be explained by other genes than the DMRT3 gene, or other mutations in this gene, that influences this diagonally stepping gait.
“Therefore, it is very likely that other genetic factors are involved in regulating the trocha and the Colombian trot gaits in Colombian paso horses.”
The full study team comprised Miguel Novoa-Bravo , Kim Jäderkvist Fegraeus, Marie Rhodin, Eric Strand, Luis Fernando García and Gabriella Lindgren.
Novoa-Bravo M, Jäderkvist Fegraeus K, Rhodin M, Strand E, García LF, Lindgren G (2018) Selection on the Colombian paso horse’s gaits has produced kinematic differences partly explained by the DMRT3 gene. PLoS ONE 13(8): e0202584. https://doi.org/10.1371/journal.pone.0202584