The importance of the DMRT3 ‘Gait keeper’ mutation on riding traits and gaits in Standardbred and Icelandic horses

Abstract

Previous studies have shown that a single base-pair mutation, a change from cytosine (C) to adenine (A), in the DMRT3 gene affects both the ability to show ambling and lateral gaits in a wide range of horse breeds, as well as racing performance and trotting technique in Standardbred and Nordic trotters. The variant allele is present in gaited breeds but is absent, or found at a very low frequency, in breeds used for Western-European style riding and flat racing, like the Swedish Warmblood and Thoroughbreds as well as in draught horses. This indicates that the variant allele might have a negative effect on certain riding performance traits in horses. Therefore, one aim of this study was to investigate whether the DMRT3 variant affects canter in Standardbred trotters, and to test if heterozygous horses (CA) were better suited for Western-European style riding than homozygous horses (AA). Riding traits were studied in 115 Standardbred horses, and a similar study was also performed with data from 55 Nordic trotters. The results showed that CA Standardbreds had significantly better balance in canter, both collected and extended canter, than AA horses. The CA horses also got significantly higher scores for transitions in collected canter. For the rhythm we found no significant differences between the genotypes. In the Nordic trotters we were unable to establish any significant difference for canter ability.Another aim of this study was to investigate the effect of the variant allele on riding abilities and gaits in the Icelandic horse (n=446). Practically all horse breeds considered to be three-gaited have a CC genotype, in contrast Icelandic CC horses can show tölt. We therefore tested whether the variant influenced how difficult it was to initiate tölt training for these horses. It was also investigated whether the variant affects which gaits Icelandic horses choose, both at liberty and during initial training. Icelandic CC horses were significantly more difficult to train to tölt compared to CA and AA horses. The AA Icelandic horses showed the lateral gaits tölt and pace significantly more frequent, both at liberty and during initial training, than CA or CC horses. The majority of the Icelandic CC and CA horses chose trot at liberty and during initial training.