Variance component estimation on the frequency of pathologic changes in the navicular bones of Hanoverian Warmblood horses

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.     

Factors associated with the prevalence of osseous fragments in the limb joints of Hanoverian Warmblood horses

Factors associated with the prevalence of osseous fragments (OF) in fetlock and hock joints were investigated in a population of young Hanoverian Warmblood horses selected for sale at auction from 1991 to 1998. The study was based on results of a standardized radiological examination of 3127 horses. The prevalences of OF in the two joints were significantly dependent on the date, type and quality of the auction, the region of origin and on the anticipated suitability of the horses for dressage and/or show-jumping. The probability of finding OF increased with wither-height. Furthermore, there was a significant association of the individual sire with the prevalence of OF in both fetlock and hock joints, and of the maternal grandsire with the prevalence of OF in the hock joints. Consequently, both non-genetic and genetic parameters should be taken into account in order to reduce the prevalence of OF in young Warmblood riding horses.     

Estimation of genetic parameters for the prevalence of osseous fragments in limb joints of Hanoverian Warmblood horses

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 (r_g = 0.19–0.41). The genetic correlations between osseous fragments in the phalangeal joints and in HJ were negative (r_g = ?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 r_g = ?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 r_g = 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.     

Prediction of breeding values for osseous fragments in fetlock and hock joints, deforming arthropathy in hock joints, and pathologic changes in the navicular bones of Hanoverian Warmblood horses

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.     

Prevalence of osseous fragments in distal and proximal interphalangeal, metacarpo- and metatarsophalangeal and tarsocrural joints of Hanoverian Warmblood horses

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.     

Genetic analyses of the radiographic appearance of the distal sesamoid bones in Hanoverian Warmblood horses

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.     

Genetic correlations between osseous fragments in fetlock and hock joints, deforming arthropathy in hock joints and pathologic changes in the navicular bones of Warmblood riding horses

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 (r_g = 0.25 to 0.77). Negative additive genetic correlations were determined between OFF and OFH (r_g = − 0.17 to − 0.82), between OFH and DAH (r_g = − 0.14 to − 0.81), and between OFH and PCN (r_g = − 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.     

Evaluation of expected response to selection for orthopedic health and performance traits in Hanoverian Warmblood horses

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 toTIR andTID, 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.     

Heritabilities and genetic correlations between fetlock,hock and stifle osteochondrosis and fetlock osteochondral fragments in Hanoverian Warmblood horses

The main objective of this study is to estimate genetic parameters for osteochondrosis (OC) and osteochondrosis dissecans (OCD) in fetlock, hock and stifle joints as well as for palmar or plantar osteochondral fragments (POFs) and dorsodistal osteochondral fragments (DOFs) in fetlock joints. For this purpose, the results of a standardized radiographic examination of 7396 Hanoverian Warmblood horses were used. Heritabilities and genetic correlations were estimated using residual maximum likelihood (REML) under a linear animal model. Heritability estimates for OC at the different joints were at 0.17–0.34, for OCD at 0.16–0.46, for POFs at 0.19 and for DOFs at 0.22 after transformation onto the liability scale. For osteochondral fragments (OFs), lower heritabilities were estimated, especially in fetlock joints. POFs were genetically negatively correlated with OC in each joint. The size of the heritability estimates indicates that the prevalence of these radiographic findings can be reduced by breeding measures. However, differentiation among the different clinical entities is crucial to avoid underestimation of heritabilities. The analysis of genetic parameters performed in this study indicates that OC and OCD in fetlock, OC and OCD in hock, OC and OCD in stifle joints, POFs of the hindlimbs and DOFs may be treated as different traits.     

Prevalence of osteochondrosis in the limb joints of South German Coldblood horses

This study aimed to quantify the factors associated with the prevalence of the radiological signs of osteochondrosis (OC) and osteochondrosis dissecans (OCD) in South German Coldblood (SGC) horses. The prevalence of OC and OCD in fetlock and hock joints was analysed in 167 young coldblood horses with a mean age of 14 months. The presence of at least one osteochondrotic lesion (OC) in fetlock or hock joints was documented for 61.7% of the horses and 26.9% of the horses had osseus fragments. Osteochondrotic findings at the dorsal aspect of the sagittal ridge of the third metacarpal/metatarsal bone were seen in 53.9% of the horses and palmar/plantar osseous fragments in fetlock joints in 16.2% of the horses. Hock joint OC was found in 40.1% of the horses and hock OCD in 0.6%. Osteochondrotic findings in the distal part of the tibia were prevalent in 28.1% and in the lateral trochlea tali in 17.4% of the horses. The sex of the investigated horses significantly influenced the prevalence of OC in fetlock and hock joints, as well as the findings in the distal part of the tibia and lateral trochlea tali. Age at radiological examination was significant for the prevalence of OC in hock joints, palmar/plantar osseous fragments in fetlock joints and osteochondrotic findings in the distal part of the tibia. Female horses showed a 2-fold higher risk for OC in fetlock and hock joints than male horses. The distribution of the affected horses by age classes showed that radiographic signs of OC in fetlock and hock joints significantly increased at an age of about 1 year. We can conclude from our study that fetlock and hock OC is a prevalent radiographic finding in more than 1-year-old female and male SGC horses.     

An epidemiological study of myopathies in Warmblood horses

REASON FOR PERFORMING STUDY: There are few detailed reports describing muscular disorders in Warmblood horses. OBJECTIVES: To determine the types of muscular disorders that occur in Warmblood horses, along with presenting clinical signs, associated risk factors and response to diet and exercise recommendations, and to compare these characteristics between horses diagnosed with polysaccharide storage myopathy (PSSM), those diagnosed with a neuromuscular disorder other than PSSM (non-PSSM) and control horses. METHODS: Subject details, muscle biopsy diagnosis and clinical history were compiled for Warmblood horses identified from records of biopsy submissions to the University of Minnesota Neuromuscular Diagnostic Laboratory. A standardised questionnaire was answered by owners at least 6 months after receiving the muscle biopsy report for an affected and a control horse. RESULTS: Polysaccharide storage myopathy (72/132 horses) was the most common myopathy identified followed by recurrent exertional rhabdomyolysis (RER) (7/132), neurogenic or myogenic atrophy (7/132), and nonspecific myopathic changes (14/132). Thirty-two biopsies were normal. Gait abnormality, 'tying-up', Shivers, muscle fasciculations and atrophy were common presenting clinical signs. Forty-five owners completed questionnaires. There were no differences in sex, age, breed, history or management between control, PSSM and non-PSSM horses. Owners that provided the recommended low starch fat supplemented diet and regular daily exercise reported improvement in clinical signs in 68% (19/28) of horses with a biopsy submission and 71% of horses diagnosed with PSSM (15/21). CONCLUSIONS: Muscle biopsy evaluation was a valuable tool to identify a variety of myopathies in Warmblood breeds including PSSM and RER. These myopathies often presented as gait abnormalities or overt exertional rhabdomyolysis and both a low starch fat supplemented diet and regular exercise appeared to be important in their successful management. POTENTIAL RELEVANCE: Warmbloods are affected by a variety of muscle disorders, which, following muscle biopsy diagnosis can be improved through changes in diet and exercise regimes.     

Prevalence of various radiographic manifestations of osteochondrosis and their correlations between and within joints in Dutch Warmblood horses

Reasons for performing study: Osteochondrosis (OC) is the most important orthopaedic developmental disorder in horses and may manifest in several different forms. No detailed study on the prevalence and/or interrelation of these forms is available, even though these data are a prerequisite for conclusive genetic studies. Objectives: To assess the prevalence of the various manifestations of OC as detected radiographically and to evaluate possible relationships between their occurrence within the same joint and between different joints. Methods: The FP (femoropatellar), TC (tarsocrural) and MCP/MTP (metacarpophalangeal/metatarsophalangeal) joints of 811 yearlings selected randomly, descending from 32 representative stallions, were radiographed and scored for the presence and grade of osteochondrotic lesions. Results were compared at the sire, animal, joint and predilection site levels. Results: In the FP joint, the percentage of animals showing normal joint contours in all sites was 60.7%. For the TC joint and the combined MCP/MTP joints, these figures were 68.6 and 64.6%, respectively. For all joints combined, the percentage dropped to 30.5%. Sedation improved detection of OC lesions in the FP joint. There was a high correlation between the right and left joints. The correlation between flattened bone contours and fragments was considerably less. Conclusions: Scoring on a detailed scale is necessary to achieve good insight into the prevalence of OC. Observations on the right and left joints can be combined in further analyses, whereas flattened bone contours and fragments should be evaluated as statistically different disorders. Potential relevance: This study provides insight into the prevalences of various manifestations of OC and their relationships, within and between joints. These results form the basis for detailed quantitative and/or molecular genetic studies that should lead to the establishment of breeding indices and/or genetic marker sets for OC.     

Prevalence of hereditary diseases in three-year-old Swiss Warmblood horses

The objective of this study was to investigate clinical signs indicating hereditary diseases like equine sarcoid, osteochondrosis (OC) and the idiopathic laryngeal hemiplegia (ILH), and to demonstrate relationships between environment, feeding habits and conformation ("exterieur" evaluation) of the horses. For this purpose, we analyzed veterinary examinations of 403 stallions at the approvals since 1994 examined 493 three-year-old Swiss Warmblood horses, which were shown at the Swiss-Field-Tests in 2005.With the help of the owners a questionnaire on health, environment and feeding habits of the animals was completed. At the same time, the horses were assessed and graded for their "exterieur" (type, conformation, gaits) by judges of the Swiss Sporthorse breeding association. In 11.5% of horses sarcoids were found, 8.7% showed one and 2.8% several tumors.The prevalence of sarcoids in offspring of sires with known sarcoids was not significantly higher than in descendants from stallions without a known history of sarcoids. We found distended joints as a possible symptom of OC in 11.4% of the horses, 3.9% (n = 19) in both tarsal joints.We did not find a relationship between enlarged joints in the offspring and the presence of OC in the sires. Abnormal respiratory noise at work, as a possible sign for ILH, was heard only in 1.2% (n = 6). It is important to note that while we found a high number of sarcoid affected horses compared to other studies, presence of enlarged joints was not very frequent and very few horses showed abnormal respiratory noise. Additionally, we found no correlation between "exterieur" marks and the horse's general health.     

Genetic parameters for the prevalence of osteochondrosis in the limb joints of South German Coldblood horses

Heritabilities were estimated for osteochondrosis (OC) in fetlock and hock joints and palmar/plantar osseous fragments in fetlock joints of South German Coldblood (SGC) horses using Residual Maximum Likelihood (REML) under a linear animal model. The analyses were based on the results of a standardized radiographic examination of 167 SGC horses with a mean age of 14 months. The heritabilities linearly estimated and transformed onto the liability scale were for OC in fetlock joints 0.16 and for OC in hock joints 0.04. Considering fetlock and hock OC together, results in a heritability of 0.17. Palmar/plantar osseus fragments of the fetlock joints showed a heritability of 0.48. We concluded that there is most likely a genetic component in the variation of the development of osteochondrosis in fetlock and hock joints as well as for palmar/plantar osseus fragments of fetlock joints of the investigated population of SGC horses.     

Evaluation of cervical radiographs in Dutch Warmblood horses,using a novel radiographic grading system for the cervical articular process joints

Clinical and radiographic examination of the cervical spine has been of increasing interest in the prepurchase examination and clinical work-up conducted for horses. The objective of this study was to describe a grading system useful for evaluating all the cervical articular process joints (cAPJs). Additionally, the findings of the cervical radiographs (occiput, cAPJ and intercentral joint space grading, intra- and intervertebral sagittal ratios, and intervertebral disc width measurements) were reported, and their association with clinical complaints in a large group of Dutch Warmblood horses (n = 598) were investigated. Significant associations were found between cAPJ radiographic grades and clinical complaints using the chi-squared test (C2-3 [P = 0.01], C5-6 [P = 0.006], C6-7 [P < 0.001], and C7-T1 [P = 0.02]). Higher occiput grades were significantly associated with clinical complaints (chi-squared test, P = 0.005). A large variability was found for intra- and intervertebral ratios and minimum intercentral joint space in the control group, but no significant association between intercentral joint space and clinical complaints was observed using the Kruskal–Wallis test followed by post hoc testing with the Wilcoxon rank sum test with a Bonferroni correction. The main limitations of this study were that only information regarding localisation was used for the statistical analyses, without any other details of the clinical complaints. Furthermore, clinical records were retrospectively reviewed, and a bias towards cervical findings in the clinical data recordings should be considered. It was concluded that knowledge of the distribution of the radiographic findings evaluated in this study and their associated clinical relevance can be useful in reaching a science-based diagnosis in daily practice.