Prevalence, heritability and significance of musculoskeletal conformational traits in Thoroughbred yearlings

Conformational Defects in the Limbs of Menorca Purebred Horses and Their Relationship to Functionality

Limb-conformation defects significantly influence equine performance and welfare, necessitating thorough investigation for effective management. This study examines the prevalence and genetic parameters of 14 limb-conformation defects in Menorca Purebred horses using data from 1120 records (509 animals with an average age of 101.87 ± 1.74 months) collected between 2015 and 2023. Defects were evaluated using a three-class scale by three appraisers, and a Bayesian approach via Gibbs sampling was employed to estimate genetic parameters including gender, birth period, stud selection criteria, evaluation age and appraiser as fixed effects. Splay-footed forelimb and closed hocks were the most prevalent defects (67.20% and 62.53%, respectively). Horses with any of the defects analyzed have been observed to obtain significantly lower scores for both walk and trot. Heritability estimates range from 0.12 (s.d.: 0.025) for closed hock to 0.30 (s.d.: 0.054) for base narrow, confirming the genetic influences on the expression of limb conformation defects. The divergent defect in hind limbs showed the highest genetic correlations with forelimb defects (camped under, -0.69; s.d: 0.32 and camped out, 0.70; s.d: 0.27). The significant genetic correlations between defects highlight the complexity of the relationships, which requires careful consideration.

Orthopedic Diseases in the Pura Raza Española Horse: The Prevalence and Genetic Parameters of Angular Hoof Deviations

Abnormalities in hoof shape are usually connected with limb conformation defects. The role of angular hoof deviations is important for longevity in sports competitions and is increasingly recognized as a factor associated with lameness in performance horses. In this paper, we measured the prevalence of four defects related to the angulation of the hoof in the Pura Raza Española horse (PRE): splay-footed forelimb (SFF), pigeon-toed forelimb (PTF), splay-footed rear limb (SFR), and pigeon-toed rear limb (PTR). A total of 51,134 animals were studied, of which only 15.75% did not have any of the four angular hoof defects investigated, while 26.61%, 23.76%, 79.53%, and 3.86% presented SFF, PTF, SFR, and PTR, respectively. Angular defects were evaluated using two different models; model A was a linear scale composed of three categories, where 0 corresponded to the absence of defects, 1 to a minor presence of the defect and 2 to the highest degree of the defect. Model B was composed of two categories, where 0 corresponded to the absence of defects and 1 to the presence of defects, joining classes 1 and 2. We measured the factors influencing the appearance of these defects: age, inbreeding coefficient, sex, and birth stud size. The heritability of each defect was also estimated using a multivariate animal model, using the Gibbsf90+ software from the BLUPF90 family, resulting in heritability estimates of 0.18 (s.d. = 0.009), 0.20 (s.d. = 0.010), 0.11 (s.d. = 0.009), and 0.31 (s.d. = 0.010) for SFF, PTF, SFR, and PTR defects, respectively, for model A, and 0.17 (s.d. = 0.008), 0.19 (s.d. = 0.009), 0.11 (s.d. = 0.009), and 0.29 (s.d. = 0.009) for SFF, PTF, SFR, and PTR defects, respectively, for model B. Finally, the genetic correlation between the diameter of the superficial digital flexor tendon (SDFT) and the proportionality index (PI) in relation to the higher or lower prevalence of the defects was analyzed. We concluded that diameter of SDFT development is strongly correlated with inward toe conditions (PTF, PTR; P≠0 ≥ 0.95), while PI is associated with outward toe defects (SFF, SFR; P≠0 ≥ 0.95).

The osseous fusion patterns in an equine limb: A theoretical deconstruction of the evolutionary mechanisms

Adaptations in equine limbs, including fusion of its bones, such as the metapodials II and IV (splint bones) with metapodial III (cannon bone), have been debated. It is argued that cursorial adaptations in equine limbs with a progressive reduction in the number of digits lighten up the limbs and facilitate fast running. Similar fusions in other bones, such as the radius and ulna, tend to exhibit similar traits. For example, the fusion often occurs in a disto-proximal direction while leaving sharp ridges. This article proposes a model to understand the biomechanical advantages that a fused symmetric system of cannon and splint bones offers and tries to investigate osseous fusion from an evolutionary perspective. It demonstrated the uniqueness of this system from the context of symmetry and the presence of an array of parallel axes of rotation in equine limbs that amplifies the kinetic energy by maximizing the moment of inertia. The model highlighted the robustness of such an evolutionary mechanism in place and elucidated why it is a preferable construct. Furthermore, the discourse proposes a zipping action to describe the osseous fusion before making predictions on where the equine limb adaptations are perhaps heading.

Genetics of Thoroughbred Racehorse Performance

Thoroughbred horses have been selected for racing performance for more than 400 years. Despite continued selection, race times have not improved significantly during the past 60 years, raising the question of whether genetic variation for racing performance still exists. Studies using phenotypes such as race time, money earned, and handicapping, however, demonstrate that there is extensive variation within these traits and that they are heritable. Even so, these are poor measures of racing success since Thoroughbreds race at different ages and distances and on different types of tracks, and some may not race at all. With the advent of genomic tools, DNA variants are being identified that contribute to racing success. Aside from strong associations for myostatin variants with best racing distance, weak to modest associations with racing phenotypes are reported for other genomic regions. These data suggest that diverse genetic strategies have contributed to producing a successful racehorse, and genetic variation contributing to athleticism remains important. Expected final online publication date for the Annual Review of Animal Biosciences, Volume 10 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Comparison of distal forelimb conformations between Japanese Black and Holstein-Friesian newborn calves

Flexural and hyperextension deformities are congenital problems in calves. We, therefore, aimed to investigate the distal limb conformation in 1 day- and 28-day-old female Holstein-Friesian (HF) calves (n=21), male Japanese Black (JB) calves (n=15), and female JB calves (n=15). The claw angle of the forelimb dorsal claw wall in a standing position and recorded other parameters, including body weight, withers height, circumference of forelimbs, and flexor tendon thickness in the forelimbs, were measured and compared these between the three groups. At 1 day old, the mean claw angles were 51.1° in female HF calves, 47.0° in male JB calves, and 41.8° in female JB calves; the 95% confidence intervals (CIs) of the claw angles showed large distributions in all three groups. One female HF and one male JB calves showed mild flexural deformity, whereas four JB calves showed hyperextension deformity. At 28 days old, the mean claw angles were 51.7° in female HF calves, 51.2° in male JB calves, and 48.4° in female JB calves; the 95% CIs of the claw angles showed smaller distributions than those at 1 day old in all groups. For all groups, the limb deformities had improved without treatment at 28 days old. As a feature of the breed, female JB calves were apt to show hyperextended deformities inversely proportional to the body weight. These limb deformities healed spontaneously and were thought to be physiological.

Dynamic evaluation of toe-heel and medio-lateral load distribution and hoof landing patterns in sound, unshod Standardbred horses with toed-in, toed-out and normal hoof conformation

Dynamic load distribution and landing patterns play an important role in equine orthopaedics. The aim of this study was to analyse dynamic load distribution and hoof landing patterns of sound Standardbreds. Twenty-four sound, unshod Standardbreds were walked and trotted over a pressure plate to obtain the peak vertical force (PVF), vertical impulse (VI) and stance time (ST) of both forelimbs. Asymmetry indices between both forelimbs were calculated and the dynamic medio-lateral and toe-heel load distribution of the forelimbs were compared between normal, toed-in and toed-out horses. The hoof landing patterns were determined on the first loaded zone. Linear mixed models and Chi-square analysis were used for statistical analysis (α = 0.05). At walk and trot, there were no significant differences in asymmetry of PVF, VI and ST between normal (n = 9/24 horses), toed-in (n = 6/24 horses), and toed-out horses (n = 9/24 horses). In both forelimbs, a flat landing (39.6% and 70.8% at walk and trot, respectively) predominated over all hoof conformations. No significant association between hoof conformation and landing pattern was observed (P > 0.05). Toed-out horses had significantly higher loading of the medial zone at the end of the stance phase at walk than normal horses (P = 0.002). No other statistically significant differences in load distribution were observed (P > 0.05). In conclusion, flat landing was more common in Standardbred horses than previously described in Warmbloods, emphasising the need for breed-specific clinical reference data and biomechanical studies. Moreover, mild deviations in hoof conformation did not necessarily affect load distribution.

Locomotion on the edge: Structural properties of the third metacarpal in Thoroughbred and Quarter Horse racehorses and feral Assateague Island ponies

The elongated, distally tapered limbs of horses are adapted for high-speed locomotion. Because these traits are artificially selected for in modern racehorses, they operate at a morphological extreme with a high risk of fracture. Racehorses are subject to different training and racing regimes depending on their breed and gait, and are therefore an interesting model to examine bone functional adaptation under variable biomechanically intense conditions. This study compares bone structural properties in the third metacarpal (MCIII) of Thoroughbred (n = 9) and Quarter Horse (n = 11) racehorses, using feral Assateague Island ponies (n = 6) as an untrained/unraced outgroup, to determine whether structural properties reflect variable racing and training regimes. Geometric section properties and bone mineral densities were determined using peripheral quantitative CT at two diaphyseal sites and through the distal epiphysis. Diaphyseal strength of the MCIII in all three breeds does not differ relative to body size, but in the mid-diaphyseal region Thoroughbreds have higher antero-posterior relative to medio-lateral bending strength than Quarter Horses, as well as higher bone mineral densities in left MCIII epiphyses (particularly in the lateral condyle). Interestingly, all breeds have lower bone mineral densities in the lateral versus medial condyle, an inherent structural feature that may influence predisposition to fracture when running around turns. Our results suggest that despite subtle differences in bone structure between different racehorse breeds, basic morphology of the third metacarpus is relatively similar among racing and non-racing horses, possibly reflecting intense selection (natural and artificial) across domestic equids for similar structural features within distal limb elements.

Genome-Wide Association Studies Based on Equine Joint Angle Measurements Reveal New QTL Affecting the Conformation of Horses

The evaluation of conformation traits is an important part of selection for breeding stallions and mares. Some of these judged conformation traits involve joint angles that are associated with performance, health, and longevity. To improve our understanding of the genetic background of joint angles in horses, we have objectively measured the angles of the poll, elbow, carpal, fetlock (front and hind), hip, stifle, and hock joints based on one photograph of each of the 300 Franches-Montagnes (FM) and 224 Lipizzan (LIP) horses. After quality control, genome-wide association studies (GWASs) for these traits were performed on 495 horses, using 374,070 genome-wide single nucleotide polymorphisms (SNPs) in a mixed-effect model. We identified two significant quantitative trait loci (QTL) for the poll angle on ECA28 (p = 1.36 × 10⁻⁷), 50 kb downstream of the ALX1 gene, involved in cranial morphology, and for the elbow joint on ECA29 (p = 1.69 × 10⁻⁷), 49 kb downstream of the RSU1 gene, and 75 kb upstream of the PTER gene. Both genes are associated with bone mineral density in humans. Furthermore, we identified other suggestive QTL associated with the stifle joint on ECA8 (p = 3.10 × 10⁻⁷); the poll on ECA1 (p = 6.83 × 10⁻⁷); the fetlock joint of the hind limb on ECA27 (p = 5.42 × 10⁻⁷); and the carpal joint angle on ECA3 (p = 6.24 × 10⁻⁷), ECA4 (p = 6.07 × 10⁻⁷), and ECA7 (p = 8.83 × 10⁻⁷). The application of angular measurements in genetic studies may increase our understanding of the underlying genetic effects of important traits in equine breeding.

Three-dimensional CT observation of position and movability of the scapula in the horse using carcasses of Falabella

The three-dimensionally real position and movement of the scapula in the lateral side of the ribcage could not be clarified in the horse, since the body size of the horse is too large to apply the CT scanning and image analysis methods. In this study, therefore, we examined the position and the movability of scapula using a carcass of the Falabella which is one of the smallest breeds of the horse. The whole skeletal system in thoracic part of the Falabella could be three-dimensionally observed by CT scanning method. The three-dimensional images show that the scapula cranially slides and the ventral part of the scapula dorso-cranially rotates, when the shoulder joint moves to the most cranial position as simulation. The three-dimensional rotation angle was approximately 10 degrees. As a result of comparative osteology of the scapula between Falabella and the large draft horse, the infraspinous fossa was caudally enlarged in the larger draft horse, whereas the Falabella had narrower infraspinous fossa. We suggest that it may be due to the adaptational morphological change in the scapula bearing various body weights among breeds. The three-dimensional CT image analysis and the simulation in carcass contribute to the analysis of the bone movements of the horse during walking and running locomotion as well as the motion analysis from external functional-morphological data.

Application of computed tomography and stereolithography to correct a complex angular and torsional limb deformity in a donkey

OBJECTIVE

To report the evaluation, surgical planning, and outcome for correction of a complex limb deformity in the tibia of a donkey using computed tomographic (CT) imaging and a 3D bone model.

STUDY DESIGN

Case report.

ANIMALS

A 1.5-year-old, 110 kg donkey colt with an angular and torsional deformity of the right pelvic limb.

METHODS

Findings on physical examimation included a severe, complex deformity of the right pelvic limb that substantially impeded ambulation. Both hind limbs were imaged via CT, and imaging software was used to characterize the bone deformity. A custom stereolithographic bone model was printed for preoperative planning and rehersal of the surgery. A closing wedge ostectomy with de-rotation of the tibia was stabilized with 2 precontoured 3.5-mm locking compression plates. Clinical follow-up was available for 3.5 years postoperatively.

RESULTS

CT allowed characterization of the angular and torsional bone deformity of the right tibia. A custom bone model facilitated surgical planning and rehearsal of the procedure. Tibial corrective ostectomy was performed without complication. Postoperative management included physical rehabilitation to help restore muscular function and pelvic limb mechanics. Short-term and long-term follow-up confirmed bone healing and excellent clinical function.

CONCLUSION

CT imaging and stereolithography facilitated the evaluation and surgical planning of a complex limb deformity. This combination of techniques may improve the accuracy of the surgeons' evaluation of complex bone deformities in large animals, shorten operating times, and improve outcomes.

Polymorphisms in ten candidate genes are associated with conformational and locomotive traits in Spanish Purebred horses

The Spanish Purebred horses, also known as Andalusian horses, compete to the highest standards in international dressage events. Gait and conformation could be used as early selection criteria to detect young horses with promising dressage ability. Although the genetic background of equine size variation has been recently uncovered, the genetic basis of horse conformational and locomotive traits is not known, hampered by the complex genetic architecture underlying quantitative traits and the lack of phenotypic data. The aim of this study was to validate the loci associated with size in 144 Spanish Purebred horses, and to seek novel associations between loci previously associated with the development of osteochondrosis (OC) lesions and 20 conformational and locomotive traits. Ten loci were associated with different conformational and locomotive traits (LCORL/NCAPG, HMGA2, USP31, MECR, COL24A1, MGP, FAM184B, PTH1R, KLF3 and SGK1), and the LCORL/NCAPG association with size in the Spanish Purebred horse was validated. Except for HMGA2, all polymorphisms seem to influence both the prevalence of OC lesions and morphological characters, supporting the link between conformation and OC. Also, the implication of most genes in either immune and inflammatory responses and cellular growth, or ossification processes, reinforces the role that these mechanisms have in the aetiology of OC, as well as their reflection on the general conformation of the individual. These polymorphisms could be used in marker-assisted selection (MAS) programmes to improve desirable conformational traits, but taking into account their possible detrimental effect on OC prevalence.

Sequence variants of BIEC2-808543 near LCORL are associated with body composition in Thoroughbreds under training

Ligand-dependent nuclear receptor compressor-like (LCORL) encodes a transcription factor, and its polymorphisms are associated with measures of skeletal frame size and adult height in several species. Recently, the single nucleotide polymorphism (SNP) BIEC2-808543 located upstream of LCORL was identified as a genetic diagnostic marker associated with withers height in Thoroughbreds. In this study, 322 Thoroughbreds-in-training were genotyped for BIEC2-808543 to evaluate the association between genotype and body composition traits, including body weight, withers height, the ratio of body weight to withers height, chest circumference, and cannon circumference. Of these, withers height and cannon circumference were significantly associated with LCORL genotypes throughout almost the entire training period in males and females. Animals with a C/T genotype had higher withers height (maximum differences of 1.8 cm and 2.1 cm in males and females, respectively) and cannon circumstance (maximum differences of 0.65 cm and 0.48 cm in males and females, respectively) compared with animals with a T/T genotype. These results suggested that the regulation of LCORL expression influences the skeletal frame size in Thoroughbreds and thus, indirectly affects the body weight. Although LCORL and BIEC2-808543 would be useful for selective breeding in Thoroughbreds, the production of genetically modified animals and gene doping based on genetic information should be prohibited in order to maintain racing integrity.

Associations of health status and conformation with longevity and lifetime competition performance in young Swedish Warmblood riding horses: 8,238 cases (1983-2005)

OBJECTIVE

To determine associations of health status and conformation with competition longevity and lifetime performance in young Swedish Warmblood riding horses.

DESIGN

Cohort study and genetic analysis.

ANIMALS

8,238 horses.

PROCEDURES

Horses were examined for health, conformation, and performance from 1983 to 2005, when they were 4 to 5 years old, and competition results from 1983 to 2012 were evaluated. Associations between conformation, health, and talent scores of young horses and longevity (years in competition) and lifetime performance were analyzed. Odds ratios of competing later in life among horses with joint flexion test reactions were determined. Genetic correlations between young horse health, conformation, and talent scores and longevity and lifetime performance were determined.

RESULTS

Good overall 4- to 5-year-old health, conformation, and talent scores for performance were phenotypically and genetically associated with greater longevity and lifetime performance. Good health was genetically correlated (rg = 0.3) to longevity and lifetime performance. Among conformation traits, body type and movements in the trot were most strongly associated with future longevity; these were genetically correlated (rg = 0.2 to 0.3) to longevity and lifetime performance. Intermediate-sized horses were associated with highest longevity and lifetime performance. Positive flexion test results were associated with lower ORs (OR, 0.59 for moderate to severe and 0.76 for minor reactions) of competing later in life, compared with no reaction, and were associated with lower longevity (0.4 years).

CONCLUSIONS AND CLINICAL RELEVANCE

Horses with good health and conformation at a young age had better longevity in competitions than the mean. Positive correlations suggested that improvement of health and conformation of young horses will enhance their future athletic talent and performance.

Longitudinal development of equine forelimb conformation from birth to weaning in three different horse breeds

There is limited published data on conformational changes in the forelimbs of growing foals. This study was designed to describe the changes in conformation of the carpus and distal forelimb from birth to weaning in foals of three different breeds. Evaluation of the conformation of the carpus, fetlock, pastern and foot was carried out in 134 Thoroughbreds, 162 French Trotters and 98 Selle Français (French Warmblood) within 1 month of age and then at approximately 2 month intervals until weaning at approximately 6 months of age. The prevalence of limb deviations decreased from birth to weaning. Angular limb deformities were the predominant conditions in the first month (63.6% of all observed limb deviations) and flexural limb deformities were the most common abnormalities at weaning. The most frequent congenital abnormalities were carpal valgus (42.1% of the foals), fetlock valgus (31.2%), over-at-the-knee (30.8%) and dropped fetlocks (13.0%), with French Trotters and Thoroughbred foals being more affected than Selle Français foals. During the study period, the carpal and fetlock conformation became less valgus. The predominant abnormalities at weaning were fetlock valgus (19.1%), club feet (13.0%) and fetlock varus (11.2%). These observations show that carpal, fetlock and foot conformations changed substantially from birth and weaning. There were significant conformational differences between the three breeds, especially in the first months of life. An understanding of the peculiarities of specific breeds may be useful for the evaluation of individual foal conformation.

Investigation into the morphology of the third metacarpal bone in the horse

AIMS

To describe key morphological attributes of the third metacarpal bone (Mc3) of horses and to determine whether or not the symmetry of the Mc3 varied significantly between limbs of the same horse.

METHODS

Ten pairs of metacarpi were collected from slaughter facilities. The age and breed of the horses were recorded. Fixed points and axes that could be easily reproduced between bones were identified on high-quality photographic images of each bone. Using image analysis, three angles were measured. Angle gamma measured the rotation around the long axis of the diaphysis of Mc3, angle delta the angle between the dorsal long axis of the cannon bone and the surface of the condyle of Mc3, and angle theta the angle between the surface of the condyle and the long axis of the sagittal ridge of the condyle of Mc3. These angles represent some of the characteristic morphologic relationships within the equine Mc3.

RESULTS

The coefficient of variation for angles gamma, delta and theta and were 1.2%, 0.2% and 0.5%, respectively. Angle gamma was larger in the left compared with the right limb (p=0.041). Angles delta and theta were larger in the right compared with the left limb (p=0.001 and p=0.003, respectively). There was a single outlier in a left limb for angle gamma. When this was excluded from the analysis, angle gamma in the left limb was still larger than in the right limb. Angle delta was consistently greater than 90° in 19/20 metacarpi.

CONCLUSIONS

There were significant morphological differences in the Mc3 between the left and right limbs of the 10 horses examined. These findings provide some reliable reference data for future investigation. Further work is required to document these differences in a larger population of horses and to determine whether the morphology of the Mc3 is influenced by age or other factors such as use of the animal.

Variation in frontal plane joint angles in horses

REASONS FOR PERFORMING STUDY

Conformation in horses is often considered an indicator of athletic ability, performance and resistance to orthopaedic disease. Evaluation is performed in the standing horse and repeatability influenced by stance. Ground reaction forces increase in the moving horse as speed increases.

OBJECTIVES

To determine the effect of locomotion on equine carpus, tarsus, metacarpophalangeal (MCP) and metatarsophalangeal (MTP) joints in the frontal plane.

HYPOTHESIS

Valgus/varus angulation will change when moving.

MATERIALS AND METHODS

Kinematic data were collected standing, walking and trotting for 2 groups of horses. The change in angle for carpus, tarsus, MCP and MTP joints was calculated standing and midstance for each stride. Comparison of joint angles between left and right limbs, standing, walking and trotting were made. Inter- and intrahorse variations were investigated.

RESULTS

Significant differences were observed between groups of horses and left and right forelimbs. Between walk and trot, the MCP joint changed from valgus to varus, and the tarsus and MTP joints increased in valgus deformity. Between standing and walk the carpus increased in valgus deformity. Interhorse variation was significantly different, intrahorse variation was not. Variation in measurements between gaits was minimal.

CONCLUSIONS

This study validates the measurement of joint angles from the front in the walking and trotting horse using kinematic data, interhorse variation in joint angle measurements exceeding intrahorse variation. The increases in joint angles between standing and walking, and walking and trotting warrant further investigation.

Influence of foot conformation on duration of competitive life in a Dutch Warmblood horse population

REASONS FOR PERFORMING STUDY

Warmblood horse studbooks aim to breed horses with a conformation that will enable elite future sports performance, but reduce the risk of early retirement due to lameness. Negative conformational traits, such as asymmetrical or 'uneven' forefeet may possibly shorten the career of sporthorses.

OBJECTIVES

To investigate the significance of foot conformation at young age to duration of the career of sporthorses.

METHODS

Databases of the Royal Dutch Warmblood Studbook (KWPN) and of the Royal Dutch Equestrian Sports Federation (KNHS) were matched and resulted in a dataset comprising 23,116 records of horses for which their conformation scores and duration of their sports career were available. Survival analysis was used to determine which of the conformation traits had a significant effect on duration of sports career in dressage and jumping at basic and elite level.

RESULTS

Duration of competitive life was shorter for jumping than for dressage. A different set of risk factors was found for each level and discipline. The trait 'uneven feet' tended to shorten the competitive life in dressage, but was a significant risk factor at the elite level of jumping.

CONCLUSIONS

Limb conformation and, in particular, the conformation of the distal limb, are important for duration of competitive life. From the prevalence of uneven feet in sports disciplines, it may be concluded that this is an undesirable trait, particularly at the elite level of jumping, since uneven feet have a detrimental effect on the duration of competitive life in a sporthorse population.

POTENTIAL RELEVANCE

This study provided evidence that the conformation trait uneven feet has a negative effect on Warmblood jumping performance and, therefore, breeders should be encouraged to avoid this phenomenon at foal age.