How To Read Your Horse's Test Results: Equine DMRT3 "Gait" Gene

Have you ever marveled at the unique and smooth ride of a gaited horse? From the rhythmic pace to the ever-rideable tölt, each step exudes a unique quality. But have you ever wondered what lies beneath those mesmerizing gaits that only certain horses seem to have? Get ready to dive into the extraordinary world of DMRT3, and this interesting variant, the influential 'Gait Gene,' and its profound impact on a horse's innate locomotor characteristics. With a DNA test from Etalon Equine Genetics, you can find out if your horse carries this DMRT3 variant in their genetic code. You may even be surprised to discover that your traditionally non-gaited horse might be hiding some secrets in their DNA that lie undiscovered until their foal hits the ground with an interesting way of moving!

Read on to unravel the genetics behind DMRT3, explore its variants, and discuss the implications of the known DMRT3 variants for equine enthusiasts. So saddle up and let’s embark on a journey that will forever change the way you perceive and appreciate the natural movement of a horse!

Understanding Equine DMRT3 and its Variant: The 'Gait Gene'

The equine DMRT3 variant, also known as the “Gait Keeper Mutation” or the “Gait Gene,” holds the key to understanding the intricate mechanics behind some gaited horses’ exclusive movements. This variant in DMRT3 was identified by a research team in 2012 after analyzing DNA data from 4,396 horses across 141 different breeds.¹ The genetic mutation associated with alternative gaits was found in a wide variety of breeds across the globe, including traditionally gaited horses, but was not found in Przewalski’s horses or other ancient breeds. This suggests that the DMRT3 mutation occurred relatively recently when looking at the evolutionary history of the horse.

This variant in the DMRT3 gene itself plays a crucial role in the specific gait capabilities of a horse. A horse’s locomotion is managed by central pattern generators which are a group of specialized neurons, called a neuronal circuit, found in the spinal cord. These spinal circuits or neural pathways, ultimately control the ways in which the horse is able to move its limbs. DMRT3 is a transcription factor that helps develop these groups of neurons. Mice with an alternate version or variant of the DMRT3 gene displayed incoordination of the limbs and difficulty running at higher speeds.²

For all of you equine science nerds out there: Mutations of DMRT3 result in a premature stop codon. This means that the message to create the proteins associated with the spinal circuits is truncated, or incomplete. An incomplete or altered protein will alter or change the function of the movement or trait as compared to the “wild type” or normal.

The DMRT3 Variant and Its Influence on Gait

Horses display a wide variation in locomotion, with “gaited” breeds displaying a range of unique footfall patterns at intermediate speeds. A DMRT3 mutation has been found to have a direct impact on the type of gait a horse naturally exhibits. All horses are capable of the slowest gait, the walk, and the fastest gait, the gallop, but their intermediate gaits can vary widely. It is in this middle ground, where the well-known trot and canter reside, that unique gaits such as the pace, rack, and tölt also exist.

The horse’s ability to exhibit these particular gaits is strongly influenced and sometimes determined by variations in the genetic code. One such variation is the center of this discussion, namely the DMRT3 mutation. Although this is one mutation that has been identified, many more suspected mutations remain a mystery (for now). A point mutation, or change, from a cytosine (C) to adenine (A) within the DMRT3 gene sequence defines this particular variant. Here we will look at the wild-type, or most common allele “C” (sometimes referred to as “negative” for DMRT3), and the mutated variant, “A,” and their relationship to alternate gait characteristics.

There are three possible genotypes for this DMRT3 genetic variant. This means your horse’s Etalon DNA results will be one of the following possible combinations:

• n/n (C/C) = Non-“Gaited”. No DMRT3 variants; likely non-gaited.
• DMRT3/n (A/C) = “Gait Carrier”. One DMRT3 or “gaited” variant; may display a wide variation of locomotion, partial “gaiting” and possible difficulty with 3-beat canter, lead change, tempi changes, or gait transitions.
• DMRT3/DMRT3 (A/A) = “Gaited”. Two DMRT3 or “gaited” variants; may display “gaiting”, likely loss of 3-beat canter, and severe difficulty or inability for lead or tempi changes.

Studies have shown that most horses who are considered non-gaited are exclusively negative, possessing only the “C” allele, for the DMRT3 gene. This means that they carry two copies of the C variant for a C/C genotype. Horses with this genotype have a more typical way of moving, with distinct footfalls and rhythm at the trot and canter that differentiate them from gaited breeds. In a study of 115 Standardbred horses, a copy of the C allele is linked to a more balanced canter and higher quality transitions between the intermediate gaits.³

On the other hand, horses carrying at least one "A" variant of DMRT3 are more inclined to exhibit better coordination of ipsilateral (meaning on the same side of the body) legs. The A allele is commonly seen in gaited breeds and is responsible for the unique gaits seen in horse breeds such as the Tennessee Walking Horse and the Paso Fino. This variant allows for the smooth, gliding movements that are characteristic of these breeds, making them highly sought after for their comfortable rides. One study of 427 Nordic trotters and 621 Standardbreds found that there was a favorable link between the homozygous genotype (A/A) and positive harness racing performance, which is thought to be due to the impact that the mutation has on gait.⁴

It’s important to note that the A mutation has also been found in low frequencies amongst some traditionally non-gaited breeds such as the Arabian and Quarter Horse. In 2021, Etalon Equine Genetics genotyped 11463 individual horses across more than 88 breeds to evaluate a link between discipline and the presence of the A mutation. That study identified 18 stock-type horses that were homozygous (A/A) at DMRT3 and 520 heterozygous (C/A) horses. There was a significant association between the A/A genotype and Roping, and between the C/A genotype with Reining and Hunter horses.⁵ More research is needed to determine the impact of the A variant on these horses.

Anecdotally speaking, riders of traditionally non-gaited horses who carry a copy of the A variant have noted that their horses certainly move differently. Jeannie McDevitt, owner of Tanks a Million aka Tank, who is a registered Quarter Horse, got to know her horse down to the DNA using Etalon’s comprehensive equine genetic testing. When she received Tank’s results, McDevitt was surprised to learn that her gelding is a gait gene carrier. "I had never heard of a non-gaited horse being a ‘gait carrier’. After testing my cow horse, it all makes sense. When I’m riding him, I would have trouble with clean or smooth lead changes. He would sometimes change a stride or two late in his hind end or “pop up” with me. He also tends to be ‘lazy’ behind. I’m fortunate that Bubby Petty put a great start and a lovely feel on him in the beginning. I just assumed it was an issue I had with riding him. Now I know, it’s not all me. It’s in his DNA. Knowing this has allowed me to make sure I set him up correctly for lead changes. Our lead changes have improved dramatically! Knowing my horse, inside and out, has increased our enjoyment both inside the show pen and at home together."

The exact phenotype, or the observable traits, associated with DMRT3 mutation is, to date, somewhat controversial. Currently published research has identified this mutation as the causal variation responsible for the ability to perform intermediate lateral gaits. However, even within these studies, there were and are horses from gaited breeds, clearly displaying "gaited" movements that are C/C, or negative for this DMRT3 variant.

In the Icelandic Horse, the C variant is associated with better synchronization of diagonal legs and higher ratings of the trot and gallop whereas the A variant is associated with higher speed and coordination at the tölt (a lateral intermediate gait).⁶ Interestingly, Icelandic C/C horses are capable of demonstrating their signature four-beat gait, the tölt, but studies have shown that it seems to be more difficult for them to do so compared to their C/A or A/A counterparts. The A/A Icelandic horses showed the lateral gaits tölt and pace significantly more frequently, both at liberty and during initial training compared to C/A or C/C horses. The majority of the Icelandic C/C and C/A horses chose to trot at liberty and during initial training.

Implications of DMRT3 Variants for Equine Enthusiasts

As the scientific community continues to unravel the mysteries of different horse gaits, the connection between genetics and equine movement becomes increasingly apparent. While the discovery of DMRT3 gene variants has been groundbreaking, there is still more to be understood in terms of their influence on gait. It is an ongoing area of research that holds promise for uncovering more about the intricate relationship between genetics and a horse's natural locomotion.

This exploration into the complexities of horse gaits has significant implications for equine enthusiasts. By understanding how specific DMRT3 variants contribute to the natural gaits of horses, equestrians can make more informed decisions regarding purchasing, training, and breeding. The knowledge gained from studying these genetic factors can help preserve and enhance desired gaits within different horse breeds.

For horse breeders, the discovery of DMRT3 variants offers a new tool for selecting breeding pairs with specific gait characteristics. By identifying horses with the variant associated with a desired gait, breeders can increase the chances of producing offspring with that same gaiting abilities. This knowledge can be particularly valuable for breeders focusing on traditionally gaited horses, where specific gaits are highly valued.

In some cases, such as with Icelandics and their distinct tölt, certain gaits are deeply rooted in the heritage and cultural significance of particular breeds. By studying the DMRT3 variants associated with these gaits, breeders and enthusiasts can work together to ensure the preservation and promotion of these unique breeds. This understanding can help safeguard the genetic diversity within these breeds and maintain their distinct characteristics for future generations to enjoy.

Equestrians who are eager to develop horses with specific movement characteristics can now leverage this understanding of DMRT3 to select horses that will naturally excel at performing certain gaits and movements. With this knowledge, trainers can also optimize their training methods to enhance the natural gait of horses and improve their performance in specific disciplines. By tailoring training regimens to leverage the genetic predispositions revealed by DMRT3 variants, trainers can potentially unlock even greater athletic potential in their horses.

When we look deeper into the world of DMRT3 variants and their impact on gait, we open doors to more informed breeding decisions and training practices. Equestrians, breeders, and trainers can leverage this knowledge to enhance and preserve specific gaits in different horse breeds. As we expand our genetic understanding, we can further unlock the mysteries of different horse gaits and appreciate the inherent grace and athleticism that horses possess.

Open the Gate for the Gait Gene

Understanding the role of DMRT3 variants in determining a horse's natural gait has opened up a world of possibilities for equestrians. These genetic findings not only provide valuable insights into the mechanisms behind different gaits, but also have significant implications for breeding programs, athletic performance, and even the preservation of certain breeds and disciplines.

As our understanding of DMRT3 and its role in influencing a horse's natural gait continues to evolve, equine enthusiasts are presented with exciting opportunities. From breeding programs to athletic performance enhancement and breed preservation, the implications of DMRT3 variants are far-reaching. Embracing these genetic insights can lead to advancements in horsemanship, breed conservation, and the overall appreciation of the magnificent creatures that captivate our hearts and minds. With DMRT3, the world of equine genetics has just begun to unveil its secrets.

References

¹ Promerová, M., Andersson, L. S., Juras, R., Penedo, M. C., Reissmann, M., Tozaki, T., Bellone, R., Dunner, S., Hořín, 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., … Andersson, L. (2014). Worldwide frequency distribution of the 'Gait keeper' mutation in the DMRT3 gene. Animal genetics, 45(2), 274–282. https://doi.org/10.1111/age.12120

² Andersson, L. S., Larhammar, M., Memic, F., Wootz, H., Schwochow, D., Rubin, C. J., Patra, K., Arnason, T., Wellbring, L., Hjälm, G., Imsland, F., Petersen, J. L., McCue, M. E., Mickelson, J. R., Cothran, G., Ahituv, N., Roepstorff, L., Mikko, S., Vallstedt, A., Lindgren, G., … Kullander, K. (2012). Mutations in DMRT3 affect locomotion in horses and spinal circuit function in mice. Nature, 488(7413), 642–646. https://doi.org/10.1038/nature11399

³ Jäderkvist, K., Andersson, L. S., Johansson, A. M., Árnason, T., Mikko, S., Eriksson, S., Andersson, L., & Lindgren, G. (2014). The DMRT3 ‘Gait keeper’ mutation affects performance of Nordic and Standardbred trotters. Journal of Animal Science, 92(10), 4279-4286. https://doi.org/10.2527/jas.2014-7803

⁴ Jäderkvist, K., Holm, N., Imsland, F., Árnason, T., Andersson, L., Andersson, L. S., & Lindgren, G. (2015). The importance of the DMRT3 ‘Gait keeper’ mutation on riding traits and gaits in Standardbred and Icelandic horses. Livestock Science, 176, 33-39. https://doi.org/10.1016/j.livsci.2015.03.025

⁵ Rosa, L. P., Staiger, E. A., Martin, K., Vierra, M., Foster, G., Lundquist, E., Brooks, S. A., & Lafayette, C. (2021). Stock-type equine disciplines Hunter, Reining and Roping are associated with the A allele at the DMRT3 locus for gait phenotypes in the horse. Animal Genetics, 52(5), 773-774. https://doi.org/10.1111/age.13110

⁶ Kristjansson, T., Bjornsdottir, S., Sigurdsson, A., Andersson, L. S., Lindgren, G., Helyar, S. J., Klonowski, A. M., & Arnason, T. (2014). The effect of the 'Gait keeper' mutation in the DMRT3 gene on gaiting ability in Icelandic horses. Journal of animal breeding and genetics = Zeitschrift fur Tierzuchtung und Zuchtungsbiologie, 131(6), 415–425. https://doi.org/10.1111/jbg.12112