The gene identified as playing a central role in the ability of harness racing horses and other gaited breeds to move can also affect the quality of their canter, a Swedish study has shown.
Early last year, a research team led by Professor Leif Andersson explored the distribution of a mutation in the DMRT3 gene, which has a clear influence on movement in the gaited breeds.
The DMRT3 gene is central to the usefulness of horses to humans, as it controls a range of gaits as well as pace. Many breeds have been developed with smoothness of gait as a priority.
The researchers analyzed 4,396 horses from 141 breeds around the world and found that the “gait keeper” mutation is spread across Eurasia from Japan in the East, to the British Isles in the West, on Iceland, in both South and North America, and also in breeds from South Africa.
The mutation was found to be present in 68 of the 141 genotyped horse breeds at a frequency ranging from 1% to 100%. Breeds with a high frequency of the mutation — greater than 50% — are either classified as gaited or bred for harness racing.
Now, the research team has delved deeper into the influence of the gene mutation in Standardbred and Icelandic horses, the latter known for their multiple gaits, including the tölt.
The researchers, whose paper has been accepted for publication in the peer-reviewed Livestock Science journal, said previous studies had shown that a single base-pair mutation in the DMRT3 gene, a change from cytosine (C) to adenine (A), can affect gait as well as racing performance and trotting technique in Standardbred and Nordic trotters.
The mutation is present in the gaited breeds but is absent or rare in breeds used for Western European-style riding and flat racing, such as Thoroughbreds.
The researchers set out to explore whether the gene variation affected the cantering abilities of Standardbreds, and to test if heterozygous horses (CA) — horses that received the normal gene from one parent and the mutated gene from another — were better suited for Western European-style riding than homozygous horses (AA) — horses that had received the mutated gene from both parents.
They examined the riding traits of 115 Standardbred horses, and a similar study was also performed with data from 55 Nordic trotters.
The researchers found that CA Standardbreds had significantly better balanced canters, both collected and extended, than horses that had received the mutated gene variant from both parents (AA).
The CA horses also got significantly higher scores for transitions in collected canter.
However, for rhythm, they found no significant differences between the genotypes.
In Nordic trotters, the researchers were unable to establish any significant difference in cantering ability, but did find a strong association between the presence of the mutation and the ability of the horses to tölt and pace.
The researchers also explored the influence of the mutated gene on the riding abilities and gaits in 446 Icelandic horses, a breed which has up to five gaits — walk, trot, canter/gallop, tölt and pace.
Practically all horse breeds considered to have the standard three gaits have a CC genotype — that is, they do not carry the gait-keeper gene variation.
However, Icelandic horses missing the mutation can still tölt. The researchers examined whether the absence or presence of the mutated gene variant influenced how difficult it was to initiate tölt training in the breed.
Icelandic horses that did not have the mutated gene variant were significantly more difficult to train to tölt compared to those that had it, the researchers found.
Previous research has shown that the mutated gene variant is present in 98% of Swedish Standardbreds and 45% of Nordic trotters. The frequency of the mutation in Paso Finos, from Latin America, is also nearly 100%.
By contrast, horses used for Western European-style riding and flat racing, such as the Swedish Warmblood and Thoroughbreds, lack the variant gene.
This suggested that there was selection against the variant in breeds used for Western-European style riding or flat racing, they said.
Kim Jäderkvist, Niina Holm, Freyja Imsland, Thorvaldur Árnason, Leif Andersson, Lisa S. Andersson, Gabriella Lindgren, The importance of the DMRT3 ‘Gait keeper’ mutation on riding traits and gaits in Standardbred and Icelandic horses, Livestock Science, http://dx.doi.org/10.1016/j.livsci.2015.03.025
Promerová, M., Andersson, L. S., Juras, R., Penedo, M. C. T., Reissmann, M., Tozaki, T., Bellone, R., Dunner, S., Ho?ín, P., Imsland, F., Imsland, P., Mikko, S., Modrý, D., Roed, K. H., Schwochow, D., Vega-Pla, J. L., Mehrabani-Yeganeh, H., Yousefi-Mashouf, N., G. Cothran, E., Lindgren, G. and Andersson, L. (2014), Worldwide frequency distribution of the ‘Gait keeper’ mutation in the DMRT3 gene. Animal Genetics. doi: 10.1111/age.12120
The full study on the gait-keeper gene can be read online