Abstract: Responses to different modes of single-trait selection on a trait with identified quantitative trait locus (QTL trait) and multiple-trait selection on a QTL trait and genetically correlated binary traits were studied. The aim was to identify the selection mode which most efficiently lowered the prevalence of a QTL trait or of a QTL trait and correlated binary traits under conditions encountered in animal breeding. Simulated data resembling a multiple-trait scenario including one QTL trait in a realistic setting with respect to the number of individuals with available phenotype, genotype or phenotype and genotype information were used to study selection responses after one generation. Selection responses were defined as prevalence changes of the binary traits in the offspring of selected sires relative to the prevalence in the offspring of all sires. Simulations were performed for two different levels of heritability of the QTL trait (0.2, 0.4), two different proportions of genetic variance of this trait explained by the QTL (0.5, 0.1) and two different frequencies of the favorable QTL allele (0.5, 0.2). Genetic parameters for the simulated populations were estimated in mixed linear-threshold animal models using Gibbs sampling. Single-trait selection reduced the prevalence of the QTL trait relatively by up to 10% when based on phenotype, by up to 41% when based on genotype or genotype and phenotype, and by up to 81% when based on polygenic BV and genotype of the QTL trait. At the same time, the prevalences of the correlated binary traits were almost unchanged. Multiple-trait selection based on polygenic BV, polygenic BV and QTL genotype or overall BV simultaneously reduced the prevalences of all binary traits by 20–55%. Relative prevalence decrease of the QTL trait under multiple-trait selection was largest when selecting only sires with homozygous favorable QTL genotype and above-average total index derived from polygenic BV. Low proportions of individuals homozygous for the favorable QTL allele may limit practicability of most efficient single- and multiple-trait selection schemes, so selection of individuals with above-average BV which are homo- or heterozygous for the favorable QTL allele is recommended to quickly achieve relevant selection response, while keeping sufficient numbers of breeding animals. Advantages of combined use of phenotype and genotype information were obvious even under practical conditions of small numbers of individuals with trait information, low heritability of the QTL trait, small proportion of genetic variance explained by the QTL, and low frequency of the favorable QTL allele.

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Abstract: Simulated data were used to determine the properties of multivariate prediction of breeding values for categorical and continuous traits using phenotypic, molecular genetic and pedigree information by mixed linear–threshold animal models via Gibbs sampling. Simulation parameters were chosen such that the data resembled situations encountered in Warmblood horse populations. Genetic evaluation was performed in the context of the radiographic findings in the equine limbs. The simulated pedigree comprised seven generations and 40 000 animals per generation. The simulated data included additive genetic values, residuals and fixed effects for one continuous trait and liabilities of four binary traits. For one of the binary traits, quantitative trait locus (QTL) effects and genetic markers were simulated, with three different scenarios with respect to recombination rate (r) between genetic markers and QTL and polymorphism information content (PIC) of genetic markers being studied: r = 0.00 and PIC = 0.90 (r0p9), r = 0.01 and PIC = 0.90 (r1p9), and r = 0.00 and PIC = 0.70 (r0p7). For each scenario, 10 replicates were sampled from the simulated horse population, and six different data sets were generated per replicate. Data sets differed in number and distribution of animals with trait records and the availability of genetic marker information. Breeding values were predicted via Gibbs sampling using a Bayesian mixed linear–threshold animal model with residual covariances fixed to zero and a proper prior for the genetic covariance matrix. Relative breeding values were used to investigate expected response to multi- and single-trait selection. In the sires with 10 or more offspring with trait information, correlations between true and predicted breeding values ranged between 0.89 and 0.94 for the continuous traits and between 0.39 and 0.77 for the binary traits. Proportions of successful identification of sires of average, favourable and unfavourable genetic value were 81% to 86% for the continuous trait and 57% to 74% for the binary traits in these sires. Expected decrease of prevalence of the QTL trait was 3% to 12% after multi-trait selection for all binary traits and 9% to 17% after single-trait selection for the QTL trait. The combined use of phenotype and genotype data was superior to the use of phenotype data alone. It was concluded that information on phenotypes and highly informative genetic markers should be used for prediction of breeding values in mixed linear–threshold animal models via Gibbs sampling to achieve maximum reduction in prevalences of binary traits.

Abstract: Information on 26 434 German Warmblood horses born between 1992 and 2001 was used for multivariate genetic analyses of radiographic health, conformation and performance traits to compare different modes of single- and multiple-trait selection of sires. Results of standardized radiological examinations of 5155 Hanoverian Warmblood horses, conformation evaluations from studbook inspections of 20 603 mares, and performance evaluations from mare performance tests and auction horse inspections of 16 098 horses were used for multivariate genetic analyses. Genetic parameters were estimated with restricted maximum likelihood (REML), and relative breeding values (RBV) were predicted with best linear unbiased prediction (BLUP) in multivariate linear animal models for four radiographic health traits, three conformation traits and five performance traits. Heritability estimates for osseous fragments in fetlock joints (OFF), osseous fragments in hock joints (OFH), deforming arthropathy in hock joints (DAH) and distinct radiographic findings in the navicular bones (DNB) ranged between 0.15 and 0.35 after transformation to the liability scale. Front limb conformation, hind limb conformation, withers height, walk, trot, canter, rideability and free jumping showed heritabilities between 0.09 and 0.49 and additive genetic correlations with OFF, OFH, DAH and DNB ranging between −0.53 and +0.52. Selection of sires was based on RBV or combinations of RBV, with selection for individual traits or traits from one of the three considered trait groups being considered as single-trait selection, and selection for traits from more than one trait group being considered as multiple-trait selection. The selection modes were compared by means of the expected selection response after one generation, calculated as the relative change in the prevalences of the radiographic findings or the mean conformation or performance scores in the offspring of the selected sires when compared with the offspring of all sires. The prevalences of OFF, OFH, DAH and DNB decreased by 30% to 57% after single-trait selection and 14% to 29% after multiple-trait selection, while mean conformation and performance scores increased by up to 4%. The results indicated that it is possible to simultaneously improve the radiographic health of the limbs, limb conformation, quality of gaits and rideability. However, genetic progress in free jumping ability and style could only be achieved by single- or multiple-trait selection with focus on jumping performance.

Abstract: Results of mare performance tests in the field (MPT-F) of 10,949 mares, mare performance tests at station (MPT-S) of 1,712 mares, and inspections of horses intended for sale at riding horse auctions (AU) of 4,772 horses were used to investigate genetic correlations between corresponding performance traits. Mare performance tests were held in 1995 to 2004 and auction inspections in 1999 to 2004. Scores on a scale from 0 to 10 were given for gaits under rider (walk, trot, canter), rideability (evaluated by judging commission and test rider), free-jumping (ability, style, total), and character. Radiography results of 5,102 Hanoverian Warmblood horses were used to investigate genetic correlations between performance traits and particular radiographic findings. The radiographic findings included osseous fragments in fetlock and hock joints, deforming arthropathy in hock joints, and distinct radiographic findings in the navicular bones, which were analyzed as binary traits, and radiographic appearance of the navicular bones, which was analyzed as a quasi-linear trait. Genetic parameters were estimated multivariately in linear animal models with REML using information on the horses radiographed and their contemporaries (n = 18,609). Heritability of performance traits ranged between 0.14 and 0.61, and heritability of radiographic findings between 0.14 and 0.33. Additive genetic correlations between corresponding performance traits were close to unity for MPT-F and MPT-S, ranged from 0.81 to 0.90 for MPT-F and AU, and were 0.75 to 0.92 for MPT-S and AU. Genetic correlations between performance and radiography results were mostly close to zero. Indications of negative additive genetic correlations were observed for deforming arthropathy in hock joints and canter, rideability evaluated by test rider, jumping traits and character, and osseous fragments in hock joints and character. Selection of horses for radiological health of their limbs will assist further genetic improvement of the performance of young Warmblood riding horses.

Abstract: Simulated horse data were used to compare multivariate estimation of genetic parameters and prediction of breeding values (BV) for categorical, continuous and molecular genetic data using linear animal models via residual maximum likelihood (REML) and best linear unbiased prediction (BLUP) and mixed linear-threshold animal models via Gibbs sampling (GS). Simulation included additive genetic values, residuals and fixed effects for one continuous trait, liabilities of four binary traits, and quantitative trait locus (QTL) effects and genetic markers with different recombination rates and polymorphism information content for one of the liabilities. Analysed data sets differed in the number of animals with trait records and availability of genetic marker information. Consideration of genetic marker information in the model resulted in marked overestimation of the heritability of the QTL trait. If information on 10 000 or 5000 animals was used, bias of heritabilities and additive genetic correlations was mostly smaller, correlation between true and predicted BV was always higher and identification of genetically superior and inferior animals was – with regard to the moderately heritable traits, in many cases – more reliable with GS than with REML/BLUP. If information on only 1000 animals was used, neither GS nor REML/BLUP produced genetic parameter estimates with relative bias ≤25% and BV correlation >50% for all traits. Selection decisions for binary traits should rather be based on GS than on REML/BLUP breeding values.

Abstract: Simulated data were used to investigate the influence of the choice of priors on estimation of genetic parameters in multivariate threshold models using Gibbs sampling. We simulated additive values, residuals and fixed effects for one continuous trait and liabilities of four binary traits, and QTL effects for one of the liabilities. Within each of four replicates six different datasets were generated which resembled different practical scenarios in horses with respect to number and distribution of animals with trait records and availability of QTL information. (Co)Variance components were estimated using a Bayesian threshold animal model via Gibbs sampling. The Gibbs sampler was implemented with both a flat and a proper prior for the genetic covariance matrix. Convergence problems were encountered in > 50% of flat prior analyses, with indications of potential or near posterior impropriety between about round 10 000 and 100 000. Terminations due to non-positive definite genetic covariance matrix occurred in flat prior analyses of the smallest datasets. Use of a proper prior resulted in improved mixing and convergence of the Gibbs chain. In order to avoid (near) impropriety of posteriors and extremely poorly mixing Gibbs chains, a proper prior should be used for the genetic covariance matrix when implementing the Gibbs sampler.

Abstract: Background Requirements for successful implementation of multivariate animal threshold models including phenotypic and genotypic information are not known yet. Here simulated horse data were used to investigate the properties of multivariate estimators of genetic parameters for categorical, continuous and molecular genetic data in the context of important radiological health traits using mixed linear-threshold animal models via Gibbs sampling. The simulated pedigree comprised 7 generations and 40000 animals per generation. Additive genetic values, residuals and fixed effects for one continuous trait and liabilities of four binary traits were simulated, resembling situations encountered in the Warmblood horse. Quantitative trait locus (QTL) effects and genetic marker information were simulated for one of the liabilities. Different scenarios with respect to recombination rate between genetic markers and QTL and polymorphism information content of genetic markers were studied. For each scenario ten replicates were sampled from the simulated population, and within each replicate six different datasets differing in number and distribution of animals with trait records and availability of genetic marker information were generated. (Co)Variance components were estimated using a Bayesian mixed linear-threshold animal model via Gibbs sampling. Residual variances were fixed to zero and a proper prior was used for the genetic covariance matrix. Results Effective sample sizes (ESS) and biases of genetic parameters differed significantly between datasets. Bias of heritability estimates was -6% to +6% for the continuous trait, -6% to +10% for the binary traits of moderate heritability, and -21% to +25% for the binary traits of low heritability. Additive genetic correlations were mostly underestimated between the continuous trait and binary traits of low heritability, under- or overestimated between the continuous trait and binary traits of moderate heritability, and overestimated between two binary traits. Use of trait information on two subsequent generations of animals increased ESS and reduced bias of parameter estimates more than mere increase of the number of informative animals from one generation. Consideration of genotype information as a fixed effect in the model resulted in overestimation of polygenic heritability of the QTL trait, but increased accuracy of estimated additive genetic correlations of the QTL trait. Conclusion Combined use of phenotype and genotype information on parents and offspring will help to identify agonistic and antagonistic genetic correlations between traits of interests, facilitating design of effective multiple trait selection schemes.

Abstract: The results of a standardized radiological examination of 5231 Hanoverian Warmblood horses were used to investigate heritability of and genetic correlations between prevalent radiographic findings in the equine limbs. Radiographic findings were categorized by joint location and type of visible alterations and analyzed as all-or-none traits. Heritabilities and correlations were estimated multivariately for most prevalent radiographic findings in equine limbs using Residual Maximum Likelihood (REML) and Gibbs Sampling (GS). Linear animal models and linear sire models were used for REML; sire threshold models were used for GS analyses. Heritabilities and residual correlations from linear model analyses were transformed from observed scale to underlying liability scale. Osseous fragments were seen in fetlock joints (OFF) of 23.5% and in hock joints (OFH) of 9.2% of investigated horses. Deforming arthropathy in hock joints (DAH) was diagnosed in 12.0% and pathologic changes in navicular bones (PCN) in 25.8% of investigated horses. Heritabilities differed little between analyses with animal and sire models and with REML and GS. Ranges of heritability estimates were h2 = 0.16–0.44 with REML and h2 = 0.07–0.43 with GS. Genetic correlation estimates were larger in GS than in REML analyses. Additive genetic correlation between OFF and DAH was positive (rg = 0.25 to 0.77). Negative additive genetic correlations were determined between OFF and OFH (rg = − 0.17 to − 0.82), between OFH and DAH (rg = − 0.14 to − 0.81), and between OFH and PCN (rg = − 0.19 to − 0.26). No relevant additive genetic correlations were estimated between PCN and OFF, and between PCN and DAH. The results of the present study indicate that the prevalences of common radiographic findings in the limbs of young riding horses are relevantly influenced by genetics and probably caused by different genes. Genetic correlations between radiological health traits therefore deserve closer attention in horse breeding. The quantitatively most important radiographic findings should be concurrently considered as individual traits in order to provide for general improvement of radiological health of the limbs of young Warmblood riding horses.

Abstract: The purpose of this work was to quantify the additive genetic correlations between prevalent radiographic findings in the limbs of Warmblood riding horses and performance parameters. Data on 3725 Hanoverian Warmblood horses selected for sale at auctions in the period 1991 to 1998 were used. The numbers of annual entries (TE) and placings (TP) in tournament competitions in the period 1991 to 2002 served as measures of performance in riding sports. Multivariate genetic analyses were performed in linear animal models using restricted maximum likelihood (REML). The four most prevalent radiographic findings, i.e. osseous fragments in fetlock (OFF) and hock joints (OFH), deforming arthropathy in hock joints (DAH) and pathologic changes in navicular bones (PCN) were analysed jointly with the performance parameters, i.e. TE and TP. Additive genetic correlations between the radiographic findings and the performance in sports were in many cases close to zero. There were some indications for significantly negative, but few indications for significantly positive additive genetic correlations between radiological conditions in the equine limbs and the performance of Warmblood riding horses in dressage, show-jumping and basic build-up competitions. Breeding measures that allow for orthopaedic health traits could therefore contribute to maximize the breeding progress in terms of sport performance.

Abstract: Objective—To evaluate whether additive genetic correlations existed between certain aspects of the radiographic appearance of the distal sesamoid (navicular) bones (RNB) or between RNB and other types of radiographic changes in the limbs of Hanoverian Warmblood horses. Animals—5,157 horses. Procedures—Quasi-linear and binary traits were defined by the appearance of canales sesamoidales (CSs) and the structure and contour of the forelimb navicular bones (NBs). Prevalences of osseous fragments in the metacarphophalangeal and metatarsophalangeal (fetlock) and tarsocrural joints and deforming arthropathy in tarsal joints were analyzed as binary traits. Genetic parameters were estimated by use of multivariate linear models. Results—Heritability estimates for the RNB traits ranged from 0.10 to 0.34. Additive genetic correlations among those traits were usually close to unity. Extensive radiographic changes in the NBs, including changes in CSs and alterations in structure and contour, had correlations with less distinct radiographic changes. Negative additive genetic correlations were observed between small numbers of short and conical CSs in the central portion of the distal border of the NB and osseous fragments and arthropathy, and between most types of radiographic findings in the NBs and osseous fragments in tarsal joints. Conclusions and Clinical Relevance—The genetic bases for different types of RNB were not identical. The detection of correlations between normal RNB and findings of short and conical CSs versus deformed CSs and structural and contour changes warrants further study. Genetically justified distinction between physiologic and pathologic NB changes will increase the efficiency of selecting against NBs with radiographically apparent alterations.

Abstract: Studbook inspection (SBI) data of 20 768 German Warmblood mares and radiography results (RR) data of 5102 Hanoverian Warmblood horses were used for genetic correlation analyses. The scores on a scale from 0 to 10 were given for conformation and basic quality of gaits, resulting in 14 SBI traits which were used for the correlation analyses. The radiographic findings considered included osseous fragments in fetlock (OFF) and hock joints (OFH), deforming arthropathy in hock joints (DAH) and distinct radiographic findings in the navicular bones (DNB) which were analyzed as binary traits, and radiographic appearance of the navicular bones (RNB) which was analyzed as a quasi-linear trait. Genetic parameters were estimated multivariately in linear animal models with REML using information on 24 448 horses with SBI and/or RR records. The ranges of heritability estimates were h 2 = 0.14-0.34 for the RR traits and h 2 = 0.09-0.50 for the SBI traits. Negative additive genetic correlations of r to -0.56 were estimated between OFF and conformation of front and hind limbs and walk at hand, and between DNB and hind limb conformation. There were indications of negative additive genetic correlations between DAH and all SBI traits, but because of low prevalence and low heritability of DAH, these results require further scrutiny. Positive additive genetic correlations of r were estimated between OFF and withers height and between OFH and withers height, indicating that selection for taller horses will increase disposition to develop OFF and OFH. Selection of broodmares with regards to functional conformation will assist, but cannot replace possible selection against radiographic findings in the limbs of young Warmblood riding horses, particularly with regards to OFF.

Abstract: Genetic parameters were estimated for the prevalence of osseous fragments in distal (DIJ) and proximal interphalangeal (PIJ), fetlock (FJ) and hock joints (HJ) of Hanoverian Warmblood horses by using residual maximum likelihood (REML) with linear animal models. The analyses were based on the results of 10 standardized radiographs of all four limbs of 3725 young riding horses selected for sale at auction. Transformation factors onto the underlying liability scale were verified by a simulation study. The heritability estimates of osseous fragments on the liability scale were in the range of h2 = 0.19–0.60. Further analyses of osseous fragments in FJ and HJ were performed separately in males and females. In both sexes, the heritabilities of osseous fragments in HJ were higher (h2 = 0.41 in males, h2 = 0.25 in females) than those of osseous fragments in FJ (h2 = 0.21 in males, h2 = 0.23 in females). Osseous fragments in the phalangeal joints (DIJ, PIJ, FJ) were genetically correlated moderately positive (rg = 0.19–0.41). The genetic correlations between osseous fragments in the phalangeal joints and in HJ were negative (rg = −0.27 to −0.67). Particularly, this applied to osseous fragments in FJ in both sexes, to those in front FJ in males and to osseous fragments in front and hind FJ of females (up to rg = −1). The heritability of height at withers was estimated at h2 = 0.27–0.28. Genetic correlations between height at withers and osseous fragments in equine limb joints were mostly moderately positive (up to rg = 0.75). We conclude from our results that osseous fragments in phalangeal and hock joints are genetically different traits but sex-specific expression of osseous fragments was unlikely.

Abstract: The prevalence of osseous fragments in different limb joints was analysed in 3749 young Warmblood riding horses, which were pre-selected for sale at auction from 1991 to 1998 by the Association of Hanoverian Warmblood Breeders (Verband hannoverscher Warmblutzüchter e.V.) in Verden (Aller), Germany. The evaluation of these horses was based on a standardized radiological examination, including the distal interphalangeal (DIJ), the proximal interphalangeal (PIJ), the metacarpo- and metatarsophalangeal (MC/MTJ) and the tarsocrural joints (TCJ). In 32% of all horses at least one osseous fragment was found on these radiographs. TCJ were affected in 9.6% of the horses and MC/MTJ in 20.7%. The percentage of horses affected in the MTJ was significantly higher (13.7%) than that of horses affected in the MCJ (9.5%). The prevalences of osseous fragments were considerably lower in DIJ (4.5%) and PIJ (0.9%). Osseous fragments only occurred either in DIJ or PIJ or MC/MTJ or TCJ in 87% of the affected horses. Depending on the joint type, osseous fragments were found in analogous joints in the front and the hind limbs in up to 26% of the affected horses, whilst bilateral affection occurred in between 10% and 46% of the horses. Distribution of osseous fragments in the limb joints investigated here did not differ significantly between male and female horses. There was a significant increase in the percentage of horses with osseous fragments in MC/MTJ during the study period. The results of this study indicate the need to act against the high prevalences of osseous fragments in the limb joints of young Warmblood riding horses.

Abstract: Objective—To determine whether selection schemes accounting for orthopedic health traits were compatible with breeding progress in performance parameters in Hanoverian Warmblood horses. Animals—5,928 horses. Procedure—Relative breeding values (RBVs) were predicted for osseous fragments in fetlock (metacarpo- and metatarsophalangeal) and tarsal joints, deforming arthropathy in tarsal joints, and pathologic changes in distal sesamoid bones. Selection schemes were developed on the basis of total indices for radiographic findings (TIR), dressage (TID), and jumping (TIJ). Response to selection was traced over 2 generations of horses for dressage and jumping ability and all-purpose breeding. Development of mean RBVs and mean total indices in sires and prevalences of orthopedic health traits in their offspring were used to assess response to selection. Results—Giving equal weight to TIR and TID, TIJ, or a combined index of 60% TID and 40% TIJ, 43% to 53% of paternal grandsires and 70% to 82% of descending sires passed selection. In each case, RBVs and total indices increased by as much as 9% in selected sires, when compared with all sires, and prevalences of orthopedic health traits in offspring of selected sires decreased relatively by as much as 16%. When selection was exclusively based on TID, TIJ, or TID and TIJ, percentages of selected sires were 44% to 66% in the first and 73% to 84% in the second generation and TID and TIJ increased by 9% to 10% and 19% to 23%, respectively. Conclusions and Clinical Relevance—Compared with exclusively performance-based selection, percentages of selected sires changed slightly and breeding progress in TID, TIJ, or TID and TIJ was only slightly decreased; however, prevalences of orthopedic health traits decreased in offspring of TIR-selected sires. (Am J Vet Res 2005;66:1371–1379)

Abstract: The results of a standardised radiological examination of 5928 Hanoverian Warmblood horses selected for sale at auction were used to predict relative breeding values (RBV) in the 23,662 horses included in the last four generations of the probands' pedigrees. The distribution of the RBV was investigated in the whole four-generation pedigree, in the probands and in those stallions that contributed at least three offspring to the probands. The RBV of the probands' sires were further compared with the officially published performance-based relative breeding values, i.e., total indices dressage (TID) and jumping (TIJ). The sires' level of dressage indices was considerably higher (mean TID=110) than of the jumping indices (mean TIJ=98). Total indices radiographic findings (TIR) were calculated for the sires with varying weighting given to the individual RBV. In each case, this resulted in a mean TIR of 99. Finally, total indices were derived from TIR and TID and/or TIJ in order to develop different selection schemes for all-purpose breeding and for breeding focused on dressage and show jumping. All breeding values under consideration increased by between 1% and 19% when radiographic findings were weighted with between 30% and 60% complementary to the corresponding performance parameters, and when only sires were selected with above average total indices. At the same time, the prevalences of the radiographic findings investigated here were lowered by up to 10% each. When only one radiographic finding was considered at a time, the maximum attainable response to selection was a 16–23% increase in the relative breeding values and a relative decrease in prevalences of radiographic findings of between 31% and 52%. The results of this study indicate that it is possible in horse breeding to consider simultaneously health and performance traits. Medical data should be included in the prediction of breeding values in order to improve the radiological status of today's riding horses.

Abstract: The development of 3,725 Warmblood riding horses selected for sale at auction in 1991–1998 was investigated on the basis of competition data and specifications of horse owners. Information on entries in tournament competitions and registered competition results obtained in tournaments in Germany in 1991–2002 were analyzed. The annual numbers of tournament entries and placings were used to quantify the horses' use in sports. Several factors were identified that had an influence on these performance parameters, including sex and age of the horse and discipline of use. When relating presence or absence of different radiographic findings in the limbs of the young horses to their later performance, mostly negative effects could be determined. In particular, horses affected with osseous fragments in distal interphalangeal joints, deforming arthropathy in proximal interphalangeal joints, and pathologic changes in navicular bones had on the average significantly lower numbers of entries and placings per year. Information derived from standardized questionnaires sent to actual owners of the former auction candidates provided some insight into current routines of keeping and management of Hanoverian Warmblood horses in Germany. The results of the study confirmed the fundamental importance of locomotory problems for the continuity of use of riding horses.

Abstract: Following the analysis of systematic effects, the restricted maximum likelihood (REML) approach was used to estimate genetic parameters on deforming arthropathies in distal (DIJ) and proximal interphalangeal (PIJ), fetlock (FJ) and hock joints (HJ) under both linear animal and linear sire models. The data comprised of the results of a standardized radiological examination of 3748 young Hanoverian Warmblood horses selected for sale at auction as riding horses. Of the horses 17.7% showed radiographic findings indicative of degenerative joint disease in at least one of the examined joints. HJ were found to be most often affected. The examiner as well as the date of the auction had a significant influence on the prevalence of documented radiological findings. Only deformations in DIJ appeared to be significantly dependent on the age of horse, with older horses being more often affected. With increasing height at withers the probability to show deformations of DIJ or PIJ tended to increase. Having genes of the Holstein Warmblood resulted in a higher probability to show deforming arthropathies in DIJ. The higher the proportion of Thoroughbred genes, the more likely was the horse to present slight HJ deformations (HJ I). Neither male and female founder animals nor sex, suitability or region of origin of the horse significantly influenced the prevalences of deforming arthropathies in the investigated joints. Sire effect had a significant influence on moderate alterations of HJ (HJ II). The estimation of genetic parameters was performed multivariately, including height at withers as a separate trait. When analysing deforming arthropathies in males and females together, the heritability estimates were in the range of h2 = 0.10–0.36. Separate analyses for HJ deformations in males and females revealed noticeable sex differences. Additive genetic correlations between radiological findings in HJ and in phalangeal joints (DIJ, PIJ, FJ) were estimated to be moderately positive. However, conflicting results were obtained for the additive genetic correlations between deforming arthropathies and height at withers.

Abstract: The results of a standardized radiological examination of 3748 young Hanoverian Warmblood horses selected for sale at auction as riding horses were used to quantify the influence of systematic effects on and to estimate genetic parameters for the prevalence of pathologic changes in the navicular bones. Radiographic findings in the navicular bones of the front limbs were analyzed as all-or-none traits. The pathologic changes were mostly classified as slight [PCN(I); 14.9%], less often as moderate [PCN(II); 5.3%] or severe [PCN(III); 1.8%]. Date and year of auction had a significant influence on the prevalence of documented radiographic findings. The prevalence of PCN(I) was further significantly dependent on the examiner, the type and the quality of auction. PCN(II) was significantly more prevalent in male than in female horses. The age, the anticipated suitability and the region of origin of the horses did not have any significant influence on the prevalence of pathologic changes in navicular bones. A higher percentage of genes of the Hanoverian and the Holstein Warmblood horse increased the probability of PCN(I) classification. A significant influence of the sire was found for PCN(I) and PCN(II), and of the male founder for PCN(II) and PCN(III). The female founder was significant only for PCN(II). In general, radiographic findings of any severity in front left and right navicular bones were significantly correlated with each other. Restricted maximum likelihood (REML) was used for the estimation of genetic parameters. The analyses were performed multivariately in linear animal and sire models including height at withers as a separate trait. Heritability estimates for the prevalence of PCN(I), PCN(II) and PCN(III) of horses of both sexes ranged between h2 = 0.09 and 0.21. When distinguishing between findings in males and females, somewhat implausible estimates were obtained for PCN(II) in females, which might have been caused by their low prevalence. The additive genetic correlations between the investigated traits indicated that radiographic findings consistent with navicular syndrome have a uniform genetic pattern in males and in females, and irrespective of their severity. However, their genetic correlation to height at withers was found to be inconsistent and, therefore, not to be utilizable for selection.