Genetic analyses of movement traits in German warmblood horses

The breeding goals of warmblood horses today focus on the performance in riding sport and quality of gaits has considerable impact on the value of a horse. Regardless of the intended use of the horse, correct gaits and balanced movement belong to the most important and basic qualities of a riding horse. Findings indicating in coordination or impaired balance were rarely, but regularly seen in horses of different ages in the context of breeding events of the Oldenburg breeding societies. The standard evaluation and selection procedures which are based on subjective scorings of rather generally defined traits were obviously not suitable to eliminate certain unfavorable movement characteristics. Knowledge on prevalences and distributions was needed to answer the question of the possible role of genetic factors. Detailed movement evaluations of foals and mares were used to define and analyze new movement traits, which may serve as measures of impaired balance. Furthermore investigations were undertaken analyzing the correlations between the new assessed movement traits and the standard conformation and performance traits routinely assessed during studbook inspections and mare performance tests in the field. Performance information on 2,758 mares, mostly 3-4 years-olds that had completed mare performance tests (MPT) was used for genetic analyses focusing on options to improve existing breeding programs through refined trait definition. For all mares, scores on a scale from 1 to 10 were available for walk, trot, canter, rideability, and free jumping, with gait scores representing means from evaluation during free movement (F) and under rider (R). Distinct F and R gait scores were used to investigate the effect of evaluation type on variance components. Genetic parameters were estimated with residual maximum likelihood (REML) in multivariate linear animal models. Heritability estimates for the MPT traits ranged from 0.19 (rideability) to 0.57 (free-jumping). For the gaits heritabilities were similar (canter) or higher (walk, trot) for F scores than for corresponding R scores. The correlations between F and R scores for the same gait were found to be closer additive genetically (rg = 0.7-0.9) than phenotypically (rp = 0.4-0.6), but may indicate F and R scores may not represent exchangeable measures of the same trait. Further correlation analyses revealed moderately to highly positive additive genetic correlations between gaits and rideability for both F and R scores, whereas additivee genetic correlations between walk and canter and between trot and free jumping was relevantly dependent on evaluation type. Because selection of riding horses represents multiple-trait selection, better reflection of covariances between selection traits will help maximizing the overall breeding progress. According to our results, Warmblood breeding may therefore benefit from refinement of trait definition with clear distinction between gait evaluation during free movement and under rider. For defining new movement traits detailed movement evaluations of 3,374 warmblood foals and 2,844 mares were further performed in connection with regular breeding events of the Oldenburg horse breeding societies in 2009 and 2010. Unfavorable movement characteristics considered indicative for impaired balance were noted by a special judge (SJ) and the regular judges of the breeding events (RJ) and served as the basis for definition of new movement traits. Detailed movement information showed that more severe findings like irregular motion pattern in hind legs (HM) or irregularity in general motion pattern (GM) occurred only sporadically (prevalences of 1-2%). Irregular tail tone or posture (TTP) was documented for 4% of the foals and 5% of the mares, resulting in prevalences of the comprehensive trait indications of imbalance (IMB) of 6.2% (foals) and 5.5% (mares). Binary coding was used for all traits, and genetic parameters were estimated bivariately in linear animal models with residual maximum likelihood (REML). Comparative analyses between judges revealed that differences between trait definitions of SJ and RJ were larger in the mares than in the foals, but justified combined use of SJ and RJ information in both age groups. Heritability estimates for the movement traits ranged on the original scale from 0.02 to 0.26 in the foals and from 0.03 to 0.12 in the mares, with heritabilities for IMB on the underlying liability scale of 0.46 (foals) and 0.22 (mares). Comparative analyses between age groups indicated that common genetic factors may be responsible for findings of impaired balance in foals and mares. Information on the new movement traits reflecting unfavorable movement characteristics for 3,374 foals and 2,844 mares was used for correlation analyses with conformation information on 1,987 mares from studbook inspections (SBI) in 2009 and performance information on 2,758 mares from mare performance tests (MPT) in 2000-2008. Analyses of variance revealed few significant differences between scores for SBI and MPT traits in mares without and with indications of imbalance (IMB) in general or specific findings like irregular tail tone or posture (TTP). SBI scores for general impression and development were significantly lower and MPT scores for trot under rider tended to be higher in IMB-positive mares. Genetic parameters were estimated in linear animal models with residual maximum likelihood (REML). Additive genetic correlations and Pearson correlation coefficients between univariately predicted breeding values indicated unfavorable genetic correlations of IMB and TTP with dressage related conformation and performance traits. For SBI and MPT traits we found similarities between the correlation patterns for DME traits in foals and mares. The results implied that breeding of dressage horses may benefit from revision of current movement evaluation and consideration of specific movement characteristics.