Equine hospital data as a source for study of prevalence and heritability of osteochondrosis and palmar/plantar osseous fragments of Swedish Warmblood horses

SNP-Based Heritability of Osteochondrosis Dissecans in Hanoverian Warmblood Horses

Before the genomics era, heritability estimates were performed using pedigree data. Data collection for pedigree analysis is time consuming and holds the risk of incorrect or incomplete data. With the availability of SNP-based arrays, heritability can now be estimated based on genotyping data. We used SNP array and 1.6 million imputed genotype data with different minor allele frequency restrictions to estimate heritabilities for osteochondrosis dissecans in the fetlock, hock and stifle joints of 446 Hanoverian warmblood horses. SNP-based heritabilities were estimated using a genomic restricted maximum likelihood (GREML) method and accounting for patterns of regional linkage disequilibrium in the equine genome. In addition, we employed GREML for family data to account for different degrees of relatedness in the study population. Our results indicate that we were able to capture a larger proportion of additive genetic variance compared to pedigree-based estimates in the same population of Hanoverian horses. Heritability estimates on the linear scale for fetlock-, hock- and stifle-osteochondrosis dissecans were 0.41-0.43, 0.62-0.63, and 0.23-0.25, respectively, with standard errors of 0.11-0.14. Accounting for linkage disequilibrium patterns had an upward effect on the imputed data and a downward impact on the SNP array genotype data. GREML for family data resulted in higher heritability estimates for fetlock-osteochondrosis dissecans and slightly higher estimates for hock-osteochondrosis dissecans, but had no effect on stifle-osteochondrosis dissecans. The largest and most consistent heritability estimates were obtained when we employed GREML for family data with genomic relationship matrices weighted through patterns of regional linkage disequilibrium. Estimation of SNP-based heritability should be recommended for traits that can only be phenotyped in smaller samples or are cost-effective.

Plantar osteochondral fragments in young Standardbreds are associated with minimal joint inflammation at the time of surgical removal

BACKGROUND

Plantar osteochondral fragments (POF) are common but their effect on joint health of young Standardbreds in race training is largely unknown.

OBJECTIVES

Evaluate the inflammatory effects of POF in metatarsophalangeal joints of young Standardbreds as a step towards developing evidence-based recommendations for surgical removal.

STUDY DESIGN

Cohort study.

METHODS

Forty-nine Standardbred horses (age 11-33 months) presented for surgical removal of POF from 56 metatarsophalangeal joints. Synovial tissue collected at arthroscopy was subjected to histopathology. IL-1β, TNF-α, and PGE-2 were measured in synovial fluid using ELISA. Digital arthroscopy images were scored for inflammation. Racing performance data were retrieved from a public database.

RESULTS

Median time in race training prior to surgery was 8 weeks (IQR 4-12; range 0-40). There was minimal evidence of synovial inflammation as assessed by histopathology (median total score 2/20, IQR 0-2, range 0-5) or arthroscopy (median average total score 2.67/15, IQR 1.79-4, range 0-8.83). IL-1β was not detected in any sample. TNF-α (median 0 pg/mL, IQR 0-0) and PGE-2 (median 56.6 pg/mL, IRQ 40.5-99.8) were measured at low levels. Weeks in training prior to surgery was associated with the number of starts in the season after surgery (incidence rate ratio 1.02, 95% CI 1.00, 1.04, P = .03).

MAIN LIMITATIONS

Small sample size from a single breed with a relatively short training time prior to surgery.

CONCLUSIONS

There was minimal evidence of synovial inflammation in the metatarsophalangeal joints in this population of young Standardbred horses with POF. It is possible that POF may result in a different inflammatory response than other fragments because they are generally well-embedded in situ. These findings suggest that, in Standardbreds, race training can commence several weeks prior to surgical removal of POF with minimal detrimental effects on joint health, although further investigation of long-term effects of POF on joint health is warranted.

Influence of osteochondrosis on the longevity and racing performance of standardbred trotters and pacers

OBJECTIVE

To determine the influence of clinical osteochondrosis (OC) on the short-term (2, 3, and 4-year-old) and long-term racing performance and longevity of standardbred racehorses.

STUDY DESIGN

Retrospective case-control study.

SAMPLE POPULATION

Standardbred racehorses from a single breeding farm born between 2009 and 2017 that survived to racing age (n = 2711). Three hundred eighty-two (14%) horses were OC-affected (829 lesions confirmed arthroscopically during surgical treatment), and 2329 (86%) horses were nonaffected.

METHODS

Racing performance data were obtained from an online database and evaluated with multiple linear regression models.

RESULTS

Trotters were more likely than pacers to be affected by OC (odds ratio [OR] = 1.4, 95% CI = 1.1-1.9, P = .006). Compared with nonaffected horses, long-term OC-affected horses had 8.8 fewer starts (95% CI = -14.4 to -3.2, P = .002), 1.0 fewer wins (95% CI = -1.9 to -0.1, P = .030), and 3.8 fewer total number of first through third place finishes (95% CI = -6.2 to -1.4, P < .0001). Nonaffected horses had longer careers compared with OC-affected horses, racing 0.32 years longer (95% CI = -0.52 to -0.12, P = .002). Osteochondrosis had no impact on short-term racing performance. Horses with lesions at the distal intermediate ridge of the tibia or lateral trochlear ridge of the talus had decreased performance compared with horses without these lesions.

CONCLUSION

Pacers were less likely than trotters to be affected by OC. Affected horses had fewer starts and shorter careers, despite early surgical intervention.

CLINICAL SIGNIFICANCE

Osteochondrosis decreases long-term racing performance in racing standardbreds.

Genetics of Equine Orthopedic Disease

Orthopedic diseases are a common cause for limited exercise capacity in the horse. They often underlie genetic risk factors, which can affect bone, articular cartilage, tendons, ligaments, and adnexal structures among others. The genetic effects can directly interfere with tissue development and skeletal growth or can trigger degenerative or inflammatory processes. Many of these diseases of the locomotor system like osteochondrosis are complex and can be affected by multifactorial influences. For this reason, it is important for those performing diagnostic procedures to have a comprehensive knowledge of orthopedic diseases, their prevalence within breeds, and genetic background.

The development of locomotor kinetics in the foal and the effect of osteochondrosis

Reason for performing study

Foals stand and walk immediately after birth, but insight into the subsequent longitudinal development of their gait kinetics in the early juvenile phase and the possible influence of osteochondrosis thereon is lacking.

Objectives

To quantify gait kinetics in foals during the first half year of life, taking into account their osteochondrosis status.

Study design

Prospective, cohort study performed at a single stud farm.

Methods

Pressure plate measurements at walk and trot from 11 Dutch Warmblood foals during the first 24 weeks of life were used to determine body mass normalised peak vertical force, normalised vertical impulse and stance duration. Coefficients of variation of peak vertical force and stance duration were used as measures for gait maturity. Radiographs of tarsocrural and femoropatellar joints were taken at age 4–6 weeks and after 6 months to check for osteochondrosis. A linear mixed model was used to determine the effects of age, limb, presence of osteochondrosis and speed on gait parameters.

Results

Mean walking and trotting velocity increased over time as did stance duration and normalised vertical impulse, normalised peak vertical force values however remained relatively constant. During the first weeks of their life only the coefficient of variation of stance duration decreased significantly, while the coefficient of variation of peak vertical force did not. None of the foals was visibly lame, but the presence of osteochondrosis resulted in a temporarily but significantly reduced normalised peak vertical force.

Main limitations

This study is a relatively small sample size of one breed from a single stud farm. A stand‐alone pressure plate was used and body mass was estimated rather than measured.

Conclusions

Despite being precocious, foals need time to mature their gait. During growth, velocity at walk and trot increases, but normalised peak vertical force remains relatively constant. Although not visibly lame, a temporary reduction in normalised peak vertical force was detected in osteochondrosis positive foals using a pressure plate.

Heritability and prevalence of selected osteochondrosis lesions in yearling Thoroughbred horses

BACKGROUND

Osteochondrosis is considered multifactorial in origin, with factors such as nutrition, conformation, body size, trauma and genetics thought to contribute to its pathogenesis. Few studies have investigated the effects of genetic variability of osteochondrosis in Thoroughbreds.

OBJECTIVES

To describe the prevalence and genetic variability of a subset of osteochondrosis lesions in a group of Thoroughbred yearlings.

STUDY DESIGN

Retrospective cohort study.

METHODS

Radiographs of 1962 Thoroughbred yearlings were retrieved from clinical records obtained between 2005 and 2013. Pedigree information was obtained from the Australian Stud Book. Osteochondrosis lesions were documented in selected joints and estimates of heritability were obtained by fitting linear mixed models in ASREML software.

RESULTS

The overall prevalence of osteochondrosis was 23%. Osteochondrosis was identified in 10% of stifle joints, 6% of hock joints and 8% of fetlock joints. The heritability estimates ranged from 0 to 0.21. The largest estimates were 0.10, 0.14, 0.16 and 0.21 for lesions of the distal intermediate ridge of the tibia, dorso-proximal proximal phalanx (P1), any stifle osteochondrosis, and lesions of the lateral trochlear ridge of the distal femur, respectively. Although calculated heritability estimates had high standard errors, meta-analyses combining the present results with published estimates were significant at 0.10, 0.17, 0.15 and 0.20 for stifle, tarsal, fetlock and these joints combined, respectively. In addition, there was a permanent environment attributable to the dam effect.

MAIN LIMITATIONS

Inclusion criteria were based on radiographic findings in specific joints at a specific age range in Thoroughbreds.

CONCLUSIONS

The present results indicate that only a proportion of osteochondrosis in Thoroughbreds is heritable. The permanent environment effects of the dam were observed to have effects on some categories of osteochondrosis.

The genetics of equine osteochondrosis

Osteochondrosis (OC) develops in growing horses due to disturbed differentiation and maturation of cartilage, particularly at the predilection sites of the fetlock, hock and stifle joints. Horses with osteochondrotic lesions are at a high risk of developing orthopaedic problems later in life. This article briefly reviews the published heritability estimates for OC and offers perspectives for selection in the horse industry. Heritabilities for OC in Warmblood and Standardbred horses have been estimated at 0.1-0.4 in animal threshold models. Whole genome scans using microsatellites have identified 14 quantitative trait loci (QTL) and the eight most important QTL have been refined using dense marker maps. Genome-wide association studies with single nucleotide polymorphisms revealed further QTL in Thoroughbred, Standardbred and Hanoverian horses. Only a few QTL have corresponding locations among the different breeds. Comparative genomics using positional candidate genes and next-generation-sequencing may lead to new insights into the genetic determination of equine OC and might help in understanding the molecular mechanisms of its pathogenesis. Implementation of selection schemes based on breeding values, or even genomic selection against OC, should be considered as an option for improving equine musculoskeletal health.

Equine developmental orthopaedic diseases--a genome-wide association study of first phalanx plantar osteochondral fragments in Standardbred trotters

Palmar/plantar osteochondral fragments (POF) in fetlock joints commonly affect and influence the athletic performance of horses. In this study, we used the Equine SNP50 BeadChip® to perform a genome-wide association study of metatarsophalangeal POF in 176 Norwegian Standardbred trotter yearlings. Putative quantitative trait loci (QTL) for medial and/or lateral POF, and medial POF only were identified on ECA1, 2, 7, 9 and 31, whereas for lateral POF, only on ECA7, 11, 27 and X. The moderate number of QTL evidences a complex inheritance and suggests various genes controlling POF development in medial and lateral locations.

Preliminary genetic analyses of important musculoskeletal conditions of Thoroughbred racehorses in Hong Kong

A retrospective cohort study of important musculoskeletal conditions of Thoroughbred racehorses was conducted using health records generated over a 15 year period (n=5062, 1296 sires). The prevalence of each condition in the study population was: fracture, 13%; osteoarthritis, 10%; suspensory ligament injury, 10%; and tendon injury, 19%. Linear and logistic sire and animal regression models were built to describe the binary occurrence of these musculoskeletal conditions, and to evaluate the significance of possible environmental risk factors. The heritability of each condition was estimated using residual maximum likelihood (REML). Bivariate mixed models were used to generate estimates of genetic correlations between each pair of conditions. Heritability estimates of fracture, osteoarthritis, suspensory ligament and tendon injury were small to moderate (range: 0.01-0.20). Fracture was found to be positively genetically correlated with both osteoarthritis and suspensory ligament injury. These results suggest that there is a significant genetic component involved in the risk of the studied conditions. Due to positive genetic correlations, a reduction in prevalence of one of the correlated conditions may effect a reduction in risk of the other condition.

Prevalence of clinical findings at examinations of young Swedish warmblood riding horses

BACKGROUND

Soundness of an individual horse is important for animal welfare and owner economy. However, knowledge of health status in normal horse populations is limited due to lack of systematic health recordings. The aim of the investigation was to study the prevalence of veterinary clinical findings in 4-5-year-old Swedish warmblood riding horses, and their influence on overall health scores, where associations to future longevity has been indicated.

RESULTS

The prevalence of clinical findings in 8,281 horses examined during 1983-2005 was studied according to a standardised protocol and related to overall health scores in linear statistical models. Effects of sex, age, examination event and changes over time were included. In total, 49% of the horses had clinical findings of medical health (MED), 42% in hooves (HOOF) and 74% of palpatory orthopaedic health (PALP). However, only 6%, 3% and 24% had moderate or severe findings, of MED, HOOF and PALP, respectively. Flexion test reactions were reported in 21% of the horses (5% moderate/severe), heavily influencing the overall score (H2). One fifth of these horses also had findings of unprovoked lameness while 83% had PALP findings (44% with moderate/severe findings). Acute clinical signs, i.e. heat or soreness, had a large influence on the H2 score but were rare, whereas more common clinical findings had smaller effects on overall health. Large variations in recorded health results were observed among events. A decrease in findings has occurred since 1983, in particular for PALP findings.

CONCLUSIONS

Results of occurrence and relevance of evaluated clinical findings could be used for advice on preventive actions to keep horses sound, and possibly for benchmarking, and genetic evaluation of health traits. The distinct effect of event on recorded clinical findings emphasises that further harmonisation of veterinary examinations are desirable.

Genetic analysis of clinical findings at health examinations of young Swedish warmblood riding horses

Background

Soundness is important for welfare and utility of the riding horse. Musculoskeletal disorders are the most common causes of interruption in training and of culling. Despite great importance, heritability of a majority of health traits in horses has previously not been estimated. The objective was to perform genetic analyses of medical and orthopaedic health traits in young riding horses, including estimates of heritability and genetic correlations between health traits, and to reveal possibilities for genetic evaluation of stallions for progeny health.

Results

The heritability of health traits was estimated using records from 8,238 Swedish warmblood riding horses examined as 4–5 year olds at the Riding Horse Quality Test in 1983–2005. The analyses were performed using multi-trait linear mixed animal models. The heritabilities of palpatory orthopaedic health (PALP), including effusion, swelling, heat, soreness and stiffness/atrophy, and hoof examination results (HOOF), of hoof shape and hoof wall quality, were 0.12 and 0.10, respectively. The genetic variation in these traits resulted in distinct health differences between progeny groups of stallions. The highest heritability among clinical signs of PALP was found for synovial effusions at 0.14. For systemic locations, joint related findings had the highest heritability; 0.13. The heritabilities of medical health and locomotion examination results were low, 0.02 and 0.04, respectively. A genetic improvement of health status has occurred over time but accounts only partly for the decrease in clinical findings of health during the studied period.

Conclusions

The genetic variation found in PALP and HOOF implies distinct differences between progeny groups. Thus, there are possibilities for improvement of these traits in the population through selection. The weak and non-significant correlation between PALP and HOOF suggests that both traits need to be selected for in practical breeding to improve both traits. Some genetic improvements over time have already been achieved, possibly due to regular stallion health inspections and an indirect selection for lifetime performance. For further improvements stallion breeding values for health may be introduced, based on RHQT examinations, complementary to present breeding values for performance.

Heritability estimates of tarsocrural osteochondrosis and palmar/plantar first phalanx osteochondral fragments in Standardbred trotters

REASONS FOR PERFORMING STUDY

The pathogenesis of osteochondrosis (OC) and palmar/plantar first phalanx osteochondral fragments (POFs) is multifactorial, but specific knowledge of heritability is limited.

OBJECTIVES

To improve the precision of heritability estimates and to estimate the genetic correlation between tarsocrural OC and POFs in Standardbred trotters. Further aims were to examine whether the prevalence of OC/POFs was different in the American and French lineages that have contributed to the Norwegian population, and if the prevalence was affected by heterozygosity.

STUDY DESIGN

Retrospective cohort study.

METHODS

Categorical data on tarsocrural OC and POFs from 2 radiographic studies performed in 1989 and 2007/2008 (n = 1217) were analysed with sire threshold models that included 230 sires.

RESULTS

Heritability of OC at the distal intermediate ridge of the tibia and/or the lateral trochlear ridge of the talus was estimated at 0.29 ± 0.15. For OC at the distal intermediate ridge of the tibia only, the estimate was 0.40 ± 0.17. Heritability of POFs in all 4 limbs was estimated at 0.23 ± 0.13; for metatarsophalangeal POFs this was 0.26 ± 0.13 and for medial metatarsophalangeal POFs 0.32 ± 0.14. Estimates of genetic correlation between OC and POFs ranged from 0.68 ± 0.27 to 0.73 ± 0.28 but were not significantly different from a zero-genetic correlation. Effects of lineages or heterozygosity were not observed.

CONCLUSIONS AND POTENTIAL RELEVANCE

This study confirmed a moderate to high heritability of tarsocrural OC and POF, providing further evidence of the heritable nature of these diseases. Examination of specific lesions yielded the highest heritability; therefore, breeding programmes and future genome-analysis studies should focus on predilection sites rather than the entire disease complex.

Horse-, training- and race-level risk factors for palmar/plantar osteochondral disease in the racing Thoroughbred

Reasons for performing study Palmar/plantar osteochondral disease (POD) is a common, debilitating condition in Thoroughbred racehorses; however, training- and racing-related factors associated with this disease are unknown.

Objectives To determine horse-, racing- and training-related risk factors for POD. The general hypotheses were that early training and racing, and increased intensity of racing and training, lead to increased severity of POD.

Methods The metacarpo/metatarsophalangeal joints of 164 Thoroughbred racehorses were examined at post mortem and graded for third metacarpal and metatarsal POD. The relationships between training- and racing-related factors and grade of POD in each condyle were determined using multilevel, multivariable, ordinal logistic regression models.

Results A total of 1288 condyles were graded. Factors associated with higher grades of POD were the total lifetime number of races, an increase in gallop sessions in the previous season, racing before import to Hong Kong and an increase in the number of short (8–16 weeks) between-race intervals per season. Horses in their first racing season were more likely to have lower POD grades, while horses that had a long between-race interval (greater than 16 weeks) in the season prior to euthanasia were also more likely to have lower POD grades. Lower POD grades were significantly more likely as days since last race increased up to 400 days. Age at first race was not significantly associated with grade of POD.

Conclusions and potential relevance Cumulative racing exposure and training intensity in the previous season were associated with higher grades of POD, supporting the hypothesis that the disease is due to repetitive loading. Longer between-race intervals and increased time since racing were associated with lower POD grades, which may indicate that lesions heal. Further work is required to enable optimisation of racing and training programmes to reduce the frequency and severity of this disease.

Integrating databases for research on health and performance in small animals and horses in the Nordic countries

In a world of limited resources, using existing databases in research is a potentially cost-effective way to increase knowledge, given that correct and meaningful results are gained.Nordic examples of the use of secondary small animal and equine databases include studies based on data from tumour registries, breeding registries, young horse quality contest results, competition data, insurance databases, clinic data, prescription data and hunting ability tests. In spite of this extensive use of secondary databases, integration between databases is less common. The aim of this presentation is to briefly review key papers that exemplify different ways of utilizing data from multiple sources, to highlight the benefits and limitations of the approaches, to discuss key issues/challenges that must be addressed when integrating data and to suggest future directions. Data from pedigree databases have been individually merged with competition data and young horse quality contest data, and true integration has also been done with canine insurance data and with equine clinical data. Data have also been merged on postal code level; i.e. insurance data were merged to a digitized map of Sweden and additional meteorological information added. In addition to all the data quality and validity issues inherent in the use of a single database, additional obstacles arise when combining information from several databases. Loss of individuals due to incorrect or mismatched identifying information can be considerable. If there are any possible biases affecting whether or not individuals can be properly linked, misinformation may result in a further reduction in power. Issues of confidentiality may be more difficult to address across multiple databases. For example, human identity information must be protected, but may be required to ensure valid merging of data. There is a great potential to better address complex issues of health and disease in companion animals and horses by integrating information across existing databases. The challenges outlined in this article should not preclude the ongoing pursuit of this approach.