Genetic background of temperament traits in standardbred trotters

Sammanfattning: The genetic background of temperament traits in horses has been subject for research for many years to obtain understanding of domestication, breed differences and welfare. Previous studies have found heritabilities ranging from low to moderate for temperament. There are also a few studies who have found genetic regions or genes correlated to temperament in horses, but also genes found important for performance that possibly are linked to temperament. There are various methods used in research to assess temperament. Previous studies have for example used objective methods to assess temperament such as novel object tests. Subjective temperament assessment is also a widespread method used at e.g., young horse-riding tests, but also in the form of surveys aimed at trainers or caretakers of horses. Positive attributes of using a survey are that information about temperament traits that are not expressed at test stations/field tests can be obtained, for example traits related to learning and stress. In this thesis, temperament assessments of Standardbred trotters were performed by collection of survey responses and DNA, to investigate the genetic background of 13 traits related to temperament at competition and to stress. Factor analysis was applied to find underlying variables explaining the temperament of Standardbreds. By using different statistical models, trait data obtained from a survey including 376 horses were analysed. Variance components for the temperament traits were estimated using linear animal models. In addition, the aim was to, as far as possible, prepare and sequence DNA obtained from the horses in the study. And if possible, perform an association analysis for one of the temperament traits. Three factors were extracted from the factor analysis: anxiousness, tractability, and excitability. The factor anxiousness included mainly low self-control, memory of unpleasant events and fearfulness. Having a high score for this factor was significantly correlated with performing a stereotypic behaviour. The second factor named tractability, described cooperative horses that easily learned the task of competing and had a high will to win. The third factor, excitability, was dominated by nervousness and excitability. A similar factor has previously been found in Coldblooded trotters; a breed also bred for harness racing. This gave indications of that this temperament characteristic might be favourable when competing in trotting races. Heritability estimates ranged from 0 to 0.42, where learning and cooperation were the traits with the highest heritability (h2=0.42 for both). In total, 288 samples were prepared for sequencing whereof 96 samples were sequenced. Based on the heritability estimations and trait score distributions, the trait excitability was chosen to be included in an association analysis. Significant differences between the case and control groups were found at a few loci. In conclusion, despite the small data material, genetic variation in several of the temperament traits was found and significant heritabilities could be estimated. The next step would be to correlate the traits in this thesis to performance data and to look at the genetic correlation between these traits. The heritability estimations also gave a preliminary indication on which traits could be worth studying further on a molecular genetic level. The preliminary analysis of the whole genome sequencing data showed interesting results worth further investigation with data from more horses included.