Genetic parameters of biokinematic variables at walk in the Spanish Purebred (Andalusian) horse using experimental treadmill records

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1 Available online at Livestock Science 116 (2008) Genetic parameters of biokinematic variables at walk in the Spanish Purebred (Andalusian) horse using experimental treadmill records A. Molina a,, M. Valera b, A.M. Galisteo c, J. Vivo c, M.D. Gómez a, A. Rodero a, E. Agüera c a Department of Genetics, University of Cordoba, Ctra. Madrid-Cádiz, km 396a, Córdoba, Spain b Department of Agro-Forestal Sciences, EUITA, University of Sevilla, Ctra. Utrera km 1, Sevilla, Spain c Department of Compared Anatomy and Pathology, University of Cordoba, Ctra. Madrid-Cádiz, km 396a, Córdoba, Spain Received 2 November 2006; received in revised form 21 September 2007; accepted 21 September 2007 Abstract The breeding scheme of Spanish Purebred (SPB) horses includes the selection of dressage performance as a main objective. Specific characteristics of the gaits are required for dressage aptitude and some could be selected for genetically. The gait of 130 SPB horses was recorded on a treadmill at walk (1.7 m/s). Nineteen biokinematic variables were analysed, 18 were directly measured from the video sequences and 1 estimated from the measurements. The data were used to estimate genetic parameters of gaits (heritability and genetic correlations). The aim was to select the biokinematic variables to include in the breeding scheme of this breed, based on their genetic parameters and their relation with dressage performance. The resulting heritabilities were medium-high (51.1% with heritability higher than 0.5). This implies a high response for selection which allows an indirect early selection for dressage performance. The genetic correlations are abundant and range between 0.28 and 0.99, which allows a reduction in the number of selected variables. Based on our results, a selection scheme should include: stride duration and length; fore and hindlimb duration and length; hindlimb maximum height of hoof; maximal retraction protraction range of forelimb; hindlimb stance phase duration and fore and hindlimb swing phase duration Elsevier B.V. All rights reserved. Keywords: Heritability; Genetic correlation; Equine locomotion; Treadmill 1. Introduction The Spanish Purebred (Andalusian) horse (SPB) is the most important breed of the Spanish horse cabin, with a census of 75,389 live animals included in the Corresponding author. Campus Universitario Rabanales, Ed. Gregor Mendel Planta baja, Ctra. Madrid-Cádiz km 396a, Córdoba, Spain. Tel.: ; fax: address: ge1moala@uco.es (A. Molina). stud-book (MAPyA, 2003). Today, the SPB makes up 65.96% of the national census, with a clear tendency to increase in the past few decades (Valera et al., 2005). The SPB has played a very excellent role in the formation of many European and American horse breeds. The economic importance of the industry associated with its breeding is also very high (Rodríguez, 1999). As a breed, the SPB is considered to have a big capacity to learn including harmonic movements. Its main use is as a saddle horse (Molina et al., 1999), /$ - see front matter 2007 Elsevier B.V. All rights reserved. doi: /j.livsci

2 138 A. Molina et al. / Livestock Science 116 (2008) although the SPB competes more and more in tests of Classic Dressage, where it has already reached an important international presence. Traditionally, this breed has been selected for its conformation and its saddle aptitude. A breeding program is now being developed to look for the selection of animals based on the performance in Classic Dressage competitions. For this reason, it is essential to make a genetic analysis of the biokinematic variables of the walk that allows its inclusion in the present Breeding Scheme. We performed biomechanical studies of locomotor performance in preliminary works, and compared these with other horse breeds (Galisteo et al., 1996, 1997, 1999, 2001; Miró et al., 1996). In this work we present, for the first time, the genetic parameters for 18 biokinematic variables obtained at walk in SPB horses, during experimental tests on treadmill. 2. Material and methods 2.1. Animal material and data obtaining The study was carried out on the treadmill of the Laboratory of Equine Performance Control (Veterinary Faculty of Cordoba, Spain). Functional tests were done in 130 SPB males with 4 (30.8%), 5 (23.1%), 6 (26.9%) and 7 (19.2%) years old. All were registered in the stud-book of this breed and came from 24 different studs. After the reception at the laboratory, the animals were clinically examined, with only the completely healthy animals accepted for the study. At least seven pre-experimental training sessions were performed before recording, to get a natural gait in the animal without stress in the flat treadmill following the recommendations in the literature (Buchner et al., 1994). Each horse was given a 5 warm-up. Then fifteen adhesive half-spheres were attached to the right side of the standing horse at previously defined skeletal reference points. These points were chosen, following Cano et al. (1999), to be easily identifiable and representative of the joints and radii under investigation (Fig. 1). The half-spheres were 32 mm in diameter and with a contrasting colour. Since some authors have shown that the speed at which the horses move significantly influences the linear, temporal and angular parameters of a gait (Leach and Crawford, 1983; Eaton et al., 1995; Galisteo et al., 1998), the speed was fixed at 1.7 m/s. From our previous work (Galisteo et al., 1996) this speed was considered optimal in this breed of horse. In addition, it is close to the speed established by Clayton (1995) for medium walk (1.73 m/s) in horses with high training in Classic Dressage. The recordings were made using a video camera (Hi8 Sony 5000-E, Sony Electronics Inc, Park Ridge, New Jersey, USA) with shutter speed at 1:4000. The camera was aligned in a perpendicular plane to the treadmill, with a field of view capturing all the length of the treadmill. Before recording, two markers measuring 1.2 m in height and graduated at 0.1 m were placed at a distance of 2 m in the middle of the treadmill belt to calibrate the system. The video sequences were digitised on a computer by using a real-time video grabber card (Matrox Marvel G-400-TV) (Matrox Graphics Inc, 1055 St-Regis Blvr, Dorval, Quebec, Canadá, H9P 2T4), including six complete consecutive strides of each limb. The beginning of the stride was determined visually from the video sequence, when the hoof touched the ground for each limb (Clayton, 1995). The stride parameters were obtained from the digitised videos at a rate of 50 fields/s, in a semiautomatic analysis system (SMVD 2.0) which allowed for a calculation of two-dimensional coordinates in each frame of the markers on the skin (Galisteo et al., 1998). Fig. 1. Position of the markers placed on the horse for the study of biokinematic variables at walk on treadmill. 1. Withers, 2. Tuber spina scapulae, 3. Tuberculum major humerus (pars caudalis) 4. Ligament collaterale cubiti laterale, 5. Procesus styloideus lateralis radii, 6. basis os IV metacarpale, 7. Ligament collaterale metacarpophalangi laterale, 8. margo coronalis (forelimb), 9. Tuber coxae, 10. Trochanter major femoris (pars caudalis), 11. Ligament collaterale geni laterale, 12. Malleolus lateralis tibialis, 13. Basis os IV metatarsale, 14. Ligament collaterale metatarsophalangi laterale, 15. Margo coronalis (hind limb).

3 A. Molina et al. / Livestock Science 116 (2008) Table 1 Biokinematic variables at walk, measured on the treadmill in Spanish Purebred horses Type Variable Name Temporal StD Stride duration FD Forelimb duration FStD Forelimb stance phase duration FSwD Forelimb swing phase duration FHS Forelimb halfway stance percentage HD Hindlimb duration HStD Hindlimb stance phase duration HSwD Hindlimb swing phase duration HHS Hindlimb halfway stance percentage Linear StL Stride length FL Forelimb length FMH Forelimb maximum height of hoof HL Hindlimb length HMH Hindlimb maximum height of hoof Angular FMRP Maximal retraction protraction angle of forelimb FRPR Retraction protraction range of the forelimb HmRP Minimal retraction protraction angle of hindlimbs HRPR Retraction protraction range of the hindlimb All the lengths are in centimetres (cm), the durations in seconds (s) and the angles in degrees ( ). Then data were transferred automatically to a spreadsheet to give the desired parameters. Eighteen walk variables were studied without rider: 5 linear, 9 temporal and 4 angular (Table 1). Linear and angular variables were obtained from digitalized images using the graduated references placed on the middle of the treadmill, except the forelimb and hindlimb length (FL and HL), since the speed is constant in this study and therefore it could be estimated indirectly from the fore and hindlimb duration (FL = forelimb duration velocity and HL = hindlimb duration velocity). Temporal variables were calculated directly from a video tape. The detailed methodology can be checked in Cano et al. (1999). Also maximum heights reached by the marker placed on hoofs coronet were measured (cm) in each right fore and hindlimb and stride frequency was estimated as 1/stride duration Statistical and genetic analysis A preliminary descriptive statistical analysis was performed with an ANOVA to analyse the influence of age and stud-farm in biokinematic characteristics. The previous statistical analysis of the different variables were performed by Statistica for Windows (Statsoft, Inc., 2001). In order to detect the underlying structure of the data, an Advanced Principal Components and Factor Analysis (PCA) was carried out. The main aim of the PCA is to recover a vector space of lower dimension onto which the original variables can be projected. By transforming the original variables to a smaller number of uncorrelated variables, PCA makes it easier to interpret the data and detect its particular structure. This PCA allows active and supplementary variables to be specified. Active variables are used in the derivation of the principal components; the supplementary variables (StL, StD, FL and HL) can then be projected onto the factor space computed from the active variables. The genetic parameters (heritabilities and genetic correlations) of these traits were estimated by VCE programs (Groeneveld, 1998) version 4, using a bivariate mixed animal model including birth year and stud of animal as fixed effects, and animal additive genetic effect and residual error as random effects. To complete the pedigree for the calculation of the inverse of the relationship matrix, the stud-book of the SPB horse was used, and all the registered ancestors of the evaluated animals were added until the fourth generation giving a total figure of 1503 animals. The additive genetic variance and covariance of the traits were estimated according to a Restricted Maximum Likelihood procedure (REML) using a Quasi-Newton algorithm Table 2 Descriptive statistics of 18 walk biokinematic variables on the treadmill in Spanish Purebred horses Trait Mean±s.e. Min. Max. C.V. (%) Trait Mean±s.e. Min. Max. C.V. (%) StD (s) 1.02± HD (s) 1.02± StL (m) 1.74± HStD (s) 0.66± FL (m) 1.74± HSwD (s) 0.37± FD (s) 1.02± HHS (%) 27.84± FStD (s) 0.63± HMH (cm) 12.41± FSwD (s) 0.39± FMRP ( ) ± FHS (%) 25.28± FRPR ( ) 35.81± FMH (cm) 14.65± HmRP ( ) 70.23± HL (m) 1.74± HRPR ( ) 42.09± Where: StD is Stride duration, StL is Stride length, FL is Forelimb length, FD is Forelimb duration, FStD is Forelimb stance phase duration, FSwD is Forelimb swing phase duration, FHS is Forelimb halfway stance percentage, FMH is Forelimb maximum height of hoof, HL is Hindlimb length, HD is Hindlimb duration, HStD is Hindlimb stance phase duration, HSwD is Hindlimb swing phase duration, HHS is Hindlimb halfway stance percentage, HMH is Hindlimb maximum height of hoof, FMRP is Maximal retraction protraction angle of forelimb, FRPR is Retraction protraction range of the forelimb, HmRP is Minimal retraction protraction angle of hindlimbs and HRPR is Retraction protraction range of the hindlimb.

4 140 A. Molina et al. / Livestock Science 116 (2008) Fig. 2. Advanced Principal Component factor analysis of walk biokinematic variables in Spanish Purebred horses studied on treadmill. The highest factor loadings were marked with. Where: StD is Stride duration, StL is Stride length, FL is Forelimb length, FD is Forelimb duration, FStD is Forelimb stance phase duration, FSwD is Forelimb swing phase duration, FHS is Forelimb halfway stance percentage, FMH is Forelimb maximum height of hoof, HL is Hindlimb length, HD is Hindlimb duration, HStD is Hindlimb stance phase duration, HSwD is Hindlimb swing phase duration, HHS is Hindlimb halfway stance percentage, HMH is Hindlimb maximum height of hoof, FMRP is Maximal retraction protraction angle of forelimb, FRPR is Retraction protraction range of the forelimb, HmRP is Minimal retraction protraction angle of hindlimbs and HRPR is Retraction protraction range of the hindlimb. with exact derivatives to maximise the log likelihood. An approximate standard error (SE) of the genetic parameters was estimated from the inverse of the approximation of the Hessian matrix when convergence was reached (Groeneveld, 1996). 3. Results 3.1. Description of walk parameters in SPB horses The descriptive statistics of the 18 biokinematic variables obtained on the treadmill for the SPB horses are shown in Table 2. Angular variables have presented a coefficient of variation (CV) lower than linear and temporal variables, with CV medium-high (higher than 8%). Fore and hindlimb maximum height of hoof obtained the highest CV (22.5% and 20%, respectively), whereas maximal forelimb retraction protraction angle and minimal hindlimb retraction protraction angle had the lowest CV (2.4% and 2.9%, respectively). Age and stud influence were also analysed (results not show) using an ANOVA. Age was a significant factor only for 3 variables (Fore and hindlimb maximum height of hoof and maximal retraction protraction angle of forelimb), whereas the stud has influenced all variables, except Duration of swing phase in forelimb. There is a significant interaction between age and studfarm in hindlimb swing phase duration and maximal retraction protraction angle of forelimb. Fig. 2 is a graphical representation of the main factors obtained in the study of the main components, along with the numerical results of the correlations between the factors and the variables. According to the results, factor 1, which represents 48.4% of variability, is the main factor related to a high number of the variables included in the analysis, except the fore and hindlimb halfway stance percentage that were related to factor 2 (12.8% of variability). The variables for the fore and hindlimb elevations and Forelimb swing phase duration were related to factor 3 (11.3%) Genetic parameters of biokinematic variables at walk The genetic parameters of biokinematic variables at walk (heritabilities and genetic correlations) are shown in Table 3. Globally, the heritabilities were mediumhigh, most of them (61.1%) with a level higher or equal

5 A. Molina et al. / Livestock Science 116 (2008) Table 3 Genetic parameters (heritability-h 2 - and significant genetic correlations) of 18 walk biokinematic variables at treadmill in Spanish Purebred horses Var. h 2 ±s.e. Genetic correlations StD 0.61±0.266 FMH: 0.78±0.396 FMRP: 0.92±0.350 StL 0.62±0.266 FMH: 0.78±0.371 FMRP: 0.92±0.478 FL 0.56±0.266 FMH: 0.78±0.394 FMRP: 0.91±0.719 FD 0.55±0.268 FMH: 0.79±0.408 FMRP: 0.92±0.834 FStD 0.29±0.212 HSwD: 0.98±0.263 HMH: 0.99±0.243 FMRP: 0.32±0.128 FSwD 0.29±0.192 HHS: 0.32±0.139 FHS 0.22±0.154 FMH 0.76±0.251 HL: 0.78±0.309 HD: 0.78±0.336 HStD: 0.45±0.249 HRPR: 0.79±0.408 HL 0.64±0.266 FMRP: 0.95±0.413 HD 0.65±0.272 FMRP: 0.95±0.416 HStD 0.82±0.231 HHS: 0.87±0.251 FMRP: 0.45±0.167 FRPR: 0.94±0.330 HSwD 0.43±0.291 FRPR: 0.91±0.246 HRPR: 0.28±0.186 HHS 0.44±0.296 HMH 0.23±0.217 FMRP 0.59±0.271 HRPR: 0.50±0.314 FRPR 0.61±0.263 HmRP 0.30±0.223 HRPR 0.83±0.276 Only shows the significant (pb0.005) genetic correlations. Where: StD is Stride duration, StL is Stride length, FL is Forelimb length, FD is Forelimb duration, FStD is Forelimb stance phase duration, FSwD is Forelimb swing phase duration, FHS is Forelimb halfway stance percentage, FMH is Forelimb maximum height of hoof, HL is Hindlimb length, HD is Hindlimb duration, HStD is Hindlimb stance phase duration, HSwD is Hindlimb swing phase duration, HHS is Hindlimb halfway stance percentage, HMH is Hindlimb maximum height of hoof, FMRP is Maximal retraction protraction angle of forelimb, FRPR is Retraction protraction range of the forelimb, HmRP is Minimal retraction protraction angle of hindlimbs and HRPR is Retraction protraction range of the hindlimb. to 0.5. The hindlimb retraction protraction range had the highest heritability (0.83) and the forelimb halfway stance percentage was the lowest one (0.22). The genetic correlations (Table 3) ranged between 0.28 (HSwD-HRPR) and 0.99 (FStD-HMH), and 66.67% of these correlations were negative. Forelimb maximum height of hoof and maximal retraction protraction angle were shown to have the greater number of genetic correlations with the rest of the variables (8 and 9, respectively). These were the genetic correlations of forelimb maximum height of hoof with the rest of the variables always negative. Forelimb halfway stance percentage and the minimal retraction protraction angle of hindlimb are not genetically correlated with any other variable. 4. Discussion 4.1. Description of walk parameters in SPB horses The gaits are the basic study unit in horse locomotion. Each gait (walk, trot and gallop) shows a different sequence of movement (Clayton, 1989), and therefore it must be studied separately. The walk is a gait that requires little effort, which has been barely considered in the training of sport horses. Nevertheless, it has the advantage of being very balanced, since a great coordination of movement of the limbs is required during the stride. The modification of the magnitudes, especially of the angular and linear variables, in the sense of causing a greater amplitude of movement, would lead to an increase in the locomotive efficiency, and therefore of the sport aptitude. In this work the genetic parameters of 18 kinematic variables of the walk that characterise the experimental movement in tests on treadmill for SPB horses are shown for the first time. There are no previous studies reported for other breeds. The main interest of this estimation is to obtain an indirect selection criteria that allow an early selection for the improvement of the sport aptitude in this breed. The characteristics of the walk, in spite of them being greatly influenced by the dressage level and the environmental factors, are good indicators of the abilities of the horse in standardised conditions (Miró et al., 1996). Additionally, the movement analysis at walk could be of some clinical interest, since knowledge of the locomotion qualities contributes to the detection of muscular and joint problems (Audigié et al., 2001; Chateau et al., 2002; Weishaupt et al., 2004). This work was experimentally developed on a treadmill with most environmental standard conditions fixed in advance, since the biokinematic qualities are greatly influenced by the track characteristics (Fredricson et al., 1983; Barrey et al., 1991). The age (Leach and Crawford 1983; Cano et al., 1999), sex (Holmström et al., 1990) and training level (Cano et al., 2000; Leleu et al., 2004) could influence the movement characteristics, because of this only males were used, and age and stud were also included in the analysis model, since both of them are indirect indicators of dressage level.

6 142 A. Molina et al. / Livestock Science 116 (2008) In general, according to our results, the influence of the stud-farm in biokinematic characteristics at walk is higher than the influence of the age. The differences because of age are related to the level of body development and the level of dressage. The influence of the stud-farm could be caused by the differences in training level, by the morphological differences related to the model selected and by the variations in animal handling. The differences observed by age within stud were scarce, and could be caused by the differences in the age of starting the dressage training of the animal. A general diminution of the temporal variables in comparison with previous studies made on this breed was also observed (Galisteo et al., 1996). These variations can be attributed to the differences in the methodology that was followed, since until now there have not been any studies characterizing the walk on the treadmill. The obtained stride length (1.74 m) was less than the indicated one in previous works of 1.84 m, 1.81 m and1.81m(galisteo et al., 1996, 1999, 2001) and similar to the value estimated by Barrey et al. (2002). Despite of this, it was within the range indicated by Clayton (1995) for this gait (1.57 m in collected walk and 1.95 m in extended walk). It is important to consider that this variable is less significant on the treadmill than on the racetrack (Fredricson et al., 1983). The results of the stride length and the average values obtained for fore and hindlimb length are practically equal, indicating that the walk of SPB horses is the typical average walk for an animal with these characteristics (eumetric and medium long shape). The lower stride length in our study is compensated for by a little increase in the stride frequency (0.98 s 1 ), compared with the value of 0.91 s 1 obtained in previous studies at hand-led walk (Galisteo et al., 1996, 1999, 2001). The stride duration (1.02 s), on the other hand, remains very similar (1.09 s and 1.11 s, in Galisteo et al., 1996, 2001, respectively). Fore and hindlimb duration showed values (1.02 s and 1.02 s, respectively) lower than those obtained previously (Galisteo et al., 1999) at hand-led walk in Andalusian (1.11 s and 1.12 s), Arabian (1.10 s and 1.09 s) and Anglo- Arabian horses (1.15 s and 1.15 s). This is due to the higher stride duration obtained in a previous study (Galisteo et al., 1999) for Andalusian (1.11 s), Arabian (1.10 s) and Anglo-Arabian horses (1.14 s), in relation with the values obtained in our analysis (1.02 s). In spite of the fore and hindlimb swing phase duration having values lower than those indicated previously at hand-led walk (Galisteo et al., 1999), our results for the forelimb length (1.74 m), forelimb swing phase duration (0.39 s) and hindlimb swing phase duration (0.37 s) show the excellent condition of SPB horse for dressage and common movements, and at the same time demonstrating its aptitude for exercises like passaje. According to Back et al. (1995), duration of swing phase in fore and hindlimb, measured in foals, are the more important temporal variables which appeared to be predictive for the value measured in dressage and jumping adults horses. Regarding the angular variables, maximal retraction protraction angle of forelimb and minimal retraction protraction angle of hindlimb have shown values similar ( and 70.23, respectively) to those obtained previously in this breed (Galisteo et al., 2001). They have also showed a smaller observed variability (2.4% and 2.9% respectively), which explains why they are the most homogeneous variables. Whereas the CV for fore and hindlimb retraction protraction range were high enough, which shows the presence of differences between individuals, especially in the retraction of the limbs, and therefore greater possibilities of improvement. In general, the CV of the forelimb variables are higher than those of the hindlimb. In the SPB horse, the movement of the forelimb is characterised by the amplitude of its extensions and elevations, and because of this the oscillation range of the variables is higher. Furthermore, the variation in them also has to be higher. So, fore and hindlimb maximum height of hoof have been the variables with the highest CV (22.5% and 20% respectively), and because of this the less homogeneous. In the study of the interrelations between the analysed variables at walk (Fig. 2), it can be seen how factor 1, which may be called locomotive capacity and explains 48.4% of the variations, is related to most of the studied variables (72.2%). Factor 2 (12.82% of the variability"), is related to the variables of support of the fore and hindlimb, and it could be named stability of the walk. Factor 3 (11.30%) is related to duration of swing phase in forelimb, fore and hindlimb maximum height of hoof. This factor can be named breed quality, since the movement in SPB horses is characterised by the elevation of the limbs, mainly of the forelimb (Galisteo et al., 2001), and the time that they stay elevated. These results are important for the selection of the variables that are going to be included in the breeding scheme of this breed Genetic parameters for the biokinematic variables Published studies to compare our results with were scarce, even in other breeds, since they are normally done with field data (performance test, shows or sport

7 A. Molina et al. / Livestock Science 116 (2008) activities) with the environmental factors having a greater influence. In addition, the scores are usually subjectively collected (Holmström and Philipsson, 1993; Koenen et al., 1995; Molina et al., 1999; Gerber- Olsson et al., 2000). On the other hand, it is considered that the characteristics of the walk have a lower heritability than those of trot and gallop (Bowling and Ruvinsky, 2000), since it is a complex movement influenced more by environmental factors (Barrey et al., 1993). Because of this, the heritability values shown in the consulted bibliography are usually low. So, according to the literature we found, the heritability of stride is very variable, with values between 0.12 and 0.37 in Dutch Warmblood Riding Horse (Koenen et al., 1995; Debby de Groot et al., 2002), 0.42 in German horse performance test (Jaitner and Reinhardt, 2003), 0.46 in Swedish Warmblood horses (Gerber-Olsson et al., 2000) and 0.61 in sport horses (Barrey et al., 1993). For this reason, the evaluation of the locomotive aptitude on a treadmill is optimal, since the characteristics" of the treadmill allow for the standardisation of the test and the objective measurement of the biokinematic variables, making this methodology ideal to study genetic parameters. So, according to our results, the heritabilities of walk variables in SPB horses (Table 3) have shown medium-high levels (ranged between ) when the treadmill is used. Consequently, the use of the results obtained in standardised conditions on the treadmill for the early selection can be very effective, making it possible to obtain a more reliable response than the one obtained by classic selection using means of scores in dressage tests, since a study showed a good correlation between scores and stride characteristics in dressage tests (Biau and Barrey, 2004) for young horses (4, 5 and 6 years old). In addition, the high correlations between variables enable a drastic reduction in the number of characteristics to consider in a process of genetic selection. The resulting standard errors were relatively high. This can be due to the magnitude of the parameter itself and to the limitation in the number of animals studied, caused by the complexity and labour intensity of the tests and in obtaining the necessary parameters. In spite of the lower heritability of hindlimb maximum height of hoof (0.23) as opposed to the rest of the variables, its consideration within the selective process is important. An increase in the value of this heritability would determine an increase of the protraction because it produces a greater joint flexion in the hindlimb during the swing phase, a typical characteristic of athletic horses. Forelimb maximum height of hoof and maximal retraction protraction angle of forelimb shows the greater number of genetic correlations with the rest of the variables (Table 3). It is necessary to emphasise that the significant genetic correlations of forelimb maximum height of hoof with the rest of the variables are negative. According to this, the genetic factors that act on this variable, decrease the variables related to the stride duration and amplitude, in the fore and hindlimb. However, Maximal retraction protraction angle of forelimb is positively correlated with fore and hindlimb stride durations and lengths and duration of stance phase of fore and hindlimbs, and retraction protraction range of hindlimb. For this reason, maximal retraction protraction angle of forelimb is an important variable for the selection of the aptitude for Classic Dressage, since its improvement indirectly affects other characteristics. It is, however, difficult to control, and for selection purposes, it is better to consider other variables which are genetically correlated with this, like stride duration length, fore and hindlimb duration and length, (correlations higher than 0.9). Finally, due to the results obtained in this study and the relationship of these variables with the quality of the movements, which are of great importance in dressage, we considered it indispensable to include within the Scheme of Selection of the SPB horse the following: fore and hindlimb swing phase duration and hindlimb stance phase duration. 5. Conclusions It is necessary to analyse the biokinematic at walk in SPB horses, since they condition the performance for saddle and Classic Dressage of the animals which are the main breeding aims for this horse. The results obtained in this work show that the analysis of kinematic variables at walk on treadmill allows a high response to selection, because of the high heritabilities observed. Given their importance in dressage performance, hindlimb maximum height of hoof and maximal retraction protraction angle of forelimb are important variables within the breeding scheme. Nevertheless, because they are easy to measure and their genetic correlations with the main variables, we recommend including in this scheme the following variables: stride duration and length, fore and hindlimb duration and length, and hindlimb maximum height of hoof. Inthe same way, based on our results, we set out to include hindlimb stance phase duration and fore and hindlimb swing phase duration within the Scheme of Selection because of their importance in the quality of gaits.

8 144 A. Molina et al. / Livestock Science 116 (2008) Acknowledgement This work was financed by FEDER funds through the project: Morfo-functional evaluation in the Breeding scheme of Spanish Purebred (Andalusian) horses (1FD ), awarded to the University of Cordoba (Spain). This work was partially funded by a grant from the Junta de Andalucía given to M.D. Gómez (BOJA n 120, ). References Audigié, F., Pourcelot, P., Degueurce, C., Geiger, D., Denoix, J.M., Kinematic analysis of the symmetry of limb movement in lame trotting horses. Equine Vet. J. Supp. 33, Back, W., Schamhardt, H.C., Hartman, W., Bruin, G., Barneveld, A., Predictive value of foal kinematics for the locomotor performance of adult horses. Res. Vet. Sci. 59, Barrey, E., Landjerit, B., Wolter, R., Shock and vibration during the hoof impact on different track surfaces. Equine Exerc. Physiol. 3, Barrey, E., Desliens, F., Poirel, D., Biau, S., Lemaire, S., Rivero, J.L., Langlois, B., Early evaluation of dressage ability in different breeds. Equine Vet. J. Supp. 34, Barrey, G., Galloux, P., Valette, J.P., Auvinet, B., Wolter, R., Stride characteristics of overground versus treadmill locomotion in the saddle horse. Acta Anat. 146, Biau, S., Barrey, E., Relationships between stride characteristics and scores in dressage tests. Pferdeilkunde 20, Bowling, A.T., Ruvinsky, A., The Genetics of the Horse. CAB International, Oxon, UK. Buchner, H.H., Savelberg, H.H., Schamhardt, H.C., Merkens, H.W., Barneveld, A., Kinematics of treadmill versus over ground locomotion in horses. Vet. Q. 16 (2), S87 S90. Cano, M.R., Miró, F., Vivo, J., Galisteo, A.M., Comparative biokinematic study of young and adult Andalusian horses at the trot. J. Vet. Med. A. Physiol. Pathol. Clin. Med. 46 (2), Cano, M.R., Miró, F., Agüera, E., Galisteo, A.M., Influence of training on the biokinematics in trotting Andalusian horses. Vet. Res. Commun. 24 (7), Chateau, H., Degueurce, C., Jerbi, H., Crevier-Denoix, N., Pourcelot, P., Audigié, F., Pasqui-Boutard, V., Denoix, J.M., Threedimensional kinematics of the equine interphalangeal joints: articular impact of asymmetric bearing. Vet. Res. Sci. 33 (4), Clayton, H.M., Locomotion. In: Jones, W.E. (Ed.), Equine Sport Medicine. Lea and Fiebiger, Philadelphia, pp Clayton, H.M., Comparison of the stride kinematics of the collected, medium and extended walks in horses. Am. J. Vet. Res. 56, Debby de Groot, B., Ducro, E., Koenen, E., van Tartwijk, H., Evaluation of the genetic correlation between general and descriptive traits of mares. Scored at the Warmblood Studbook of the Dutch, and Performance in Showjumping and Dressage in Competition. Abstract of MSc theses of students of the Animal Breeding and Genetics group of the Wageningen Institute of Animal Sciences (WIAS).Wageningen University, Wageningen, Netherlands. Eaton, M.D., Evans, D.L., Hodgson, D.P., Reuben, J.R., Effect of treadmill incline and speed on metabolic rate during exercise in Thoroughbred horse. J. Appl. Physiol. 79, Fredricson, I., Drevemo, S., Dalin, G., Hjerten, G., Bkörne, K., Rynde, R., Treadmill for equine locomotion analysis. Equine Vet. J. 15, Galisteo, A.M., Cano, M.R., Miró, F., Vivo, J., Morales, J.L., Agüera, E., Angular joints parameters in the Andalusian horses at the walk obtained by normal videography. J. Equine Vet. Sci. 16, Galisteo, A.M., Vivo, J., Cano, M.R., Morales, J.L., Miró, F., Agüera, E., Differences between breeds Dutch Warmblood vs Andalusian Purebreed in forelimb kinematics. J. Equine Sci. 8, Galisteo, A.M., Cano, M.R., Morales, J.L., Vivo, J., Miró, F., The influence of speed and height at the withers in the kinematics of sound horses at the hand-led trot. Vet. Res. Commun. 22, Galisteo, A.M., Vivo, J., Miró, F., Morales, J.L., Monterde, J.G., Cano, M.R., Variaciones en el patrón biocinemático básico del paso de caballos de tres razas guiados de la mano. Arch. Zootec. 48 (183), Galisteo, A.M., Morales, J.L., Cano, M.R., Miró, F., Agüera, E., Vivo, J., Interbreed differences in equine forelimb kinematics at the walk. J. Vet. Med., Ser. A 48 (5), 277. Gerber-Olsson, E.G., Arnason, T., Nasholm, A., Philipsson, J., Genetic parameters for traits at performance test of stallions, and correlation with traits at progeny tests in Swedish Warmblood horses. Livest. Prod. Sci. 65, Groeneveld, E., REML VCE a multivariate multi model restricted maximum likelihood (Co) variance component estimation package, version 3.2, user's guide. In: Groeneveld, E. (Ed.), Institute of Animal Husbandry and Animal Ethology. Federal Research Center of Agriculture, Neustadt, Germany. Groeneveld, E., VCE version 4.0. A multivariate variance component estimation package. Proc. 6th World Congress on Genetics Applied to Livestock Production. Armidale, Australia. Holmström, M., Philipsson, J., Relationships between conformation, performance and health in 4-year-old Swedish Warmblood Riding Horses. Livest. Prod. Sci. 33, Holmström, M., Magunsson, L.E., Philipsson, J., Variation in conformation of Swedish Warmblood horses on conformational characteristics if elite sport horses. Equine Vet. J. 22, Jaitner, J., Reinhardt, F., National genetic evaluation for horses in Germany. 55th Annual Meeting of the E.A.A.P., Roma, Italy, August 31st September 3rd. Koenen, E.P., Van Veldhuizen, A.E., Brascamp, E.W., Genetic parameters of linear scored conformation traits and their relation to dressage and show jumping performance in the Dutch Warmblood Riding Horse population. Livest. Prod. Sci. 43, Leach, D.H., Crawford, W.H., Guidelines for the future equine locomotion research. Equine Vet. J. 15, Leleu, C., Cotrel, C., Barrey, E., Effect of age on locomotion of Standardbred trotters in training. Equine Comp. Exerc. Physiol. 1 (2), MAPyA, Estudio y caracterización del sector equino en España. Madrid. ( Infsector.aspx?lng=es). Miró, F., Morales, J.L., García Palma, G., Galisteo, A.M., Collection in the passage and piafe of Spanish Purebred horses. A preliminary report. Pferdeheilkunde, 12, Molina, A., Valera, M., Dos Santos, R., Rodero, A., Genetic parameters of morphofunctional traits in Andalusian horse. Livest. Prod. Sci. 60, Rodríguez, J.J., Aspectos socioeconómicos del mundo del caballo: la industria del caballo y nuevas perspectivas. In Congreso

9 A. Molina et al. / Livestock Science 116 (2008) Internacional del Caballo de Pura Raza Española: Ed. Fundecyt. Badajoz. Spain. Statsoft, Inc., STATISTICA (data analysis software system), version 6. Valera, M., Molina, A., Gutiérrez, J.P., Gómez, J., Goyache, F., Pedigree analysis in the Andalusian horse: population structure, genetic variability and influence of the Carthusian strain. Livest. Prod. Sci. 95, Weishaupt, M.A., Wiestner, T., Hogg, H.P., Jordan, P., Auer, J.A., Vertical ground reaction force-time histories of sound Warmblood horses trotting on a treadmill. Vet. J. 168,