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To adjust for potential overestimations in the nitrogen excretion by horses within Overseer®, a revised stock unit system has been proposed (equineRSU). These equineRSU were generated and validated using a medium-sized equine farm as a model farm. The aim of this study was to test the application of the equineRSU and seasonal stock number adjustment on a more complex farming model. Livestock numbers and management data were captured prospectively for the base property (128.8 ha) of a large multi-property commercial breeding stud (3 support properties, 556 ha total area) between June 2022 and May 2023. The monthly on-farm metabolisable energy (ME) requirement and pasture demand were deterministically modelled with both a customised feed budget using livestock class and weight or using the equineRSU and monthly adjusted stock numbers. There were multiple complex movements of horses on and off the property in the different stock classes across the year, with stock management reflecting seasonal periods of high stocking density. There was good agreement (6% variance) between actual ME demand (complex feed budget) and estimated feed demand (simplistic equineRSU model) of 4,387,187 MJ vs 4,102,770 MJ. This suggests that the equineRSU could be used on complex equine farm systems within Overseer®. [ABSTRACT FROM AUTHOR]

Summary Background Objectives Study design Methods Results Main limitations Conclusion Short incomplete parasagittal fractures of the proximal phalanx are common injuries described in racehorses and also horses not used for racing. Computed tomographic (CT) features have been described in horses not used for racing, but not in a racehorse population.To describe CT features of short incomplete parasagittal fractures of the proximal phalanx in a group of Thoroughbred racehorses.Retrospective observational study.CT images of 59 Thoroughbred racehorses diagnosed with 60 short incomplete parasagittal fractures of the proximal phalanx examined between January 2014 and February 2023 were reviewed retrospectively. Horse signalment and clinical features were retrieved from hospital records.50/60 fractures were dorsally biased unicortical fractures. Mean proximodistal fracture extension in forelimbs (13.6 mm ± 3.4) was less than in hindlimbs (17.4 mm ± 4.4) (p = 0.0019). There was no difference in fracture extension in the proximodistal direction according to age or gender. Fractures in 2‐year‐olds were shorter in dorsopalmar/−plantar direction (17.4 mm ± 6.3) than in 3‐year‐olds and older horses (21.7 mm ± 7.4) (p = 0.015). Periosteal new bone was present in 91.2% of fractures and endosteal new bone in 75%.Conclusions from this study can only confidently be applied to similar populations of racing Thoroughbred horses.Short incomplete parasagittal fractures of the proximal phalanx in Thoroughbred racehorses most commonly involve only the dorsal cortex and adjacent subchondral and cancellous bone. The distribution of fracture configurations differs from that described in horses not used for racing. [ABSTRACT FROM AUTHOR]

Summary Background Objectives Study design Methods Results Main limitations Conclusion A screening ultrasonographic examination of yearling Thoroughbred horses has been described which can be performed on farm, as an adjunct to pre‐sale yearling radiography.To compare ultrasonographic and radiographic findings in young Thoroughbred horses in the detection of osteochondrosis.Descriptive and comparative study using ultrasonography and radiography.Forty‐four horses with a mean age of 10 months underwent an ultrasonographic screening protocol of joint groups including the bilateral stifle, tarsal, carpal and metacarpophalangeal/metatarsophalangeal joints. Concurrent standardised radiographic projections of all the joints were also undertaken. A cohort of 26 of these horses had a second set of radiographs taken for yearling sales approximately 6 months later. Two reviewers reviewed all images for presence or absence of osteochondrosis lesions. Comparison of the ultrasonographic and radiographic findings was undertaken using Gwet's AC1 and the Landis and Kock scale.The principal observer identified 48 ultrasonographic lesions and 15 radiographic lesions on the initial examination. Overall, there was agreement in screening for osteochondrosis using ultrasonographic and radiographic lesions, however, with varying levels of agreement for different joint groups. Agreement for individual joint groups was almost perfect for the carpal (0.98) and metatarsophalangeal joints (0.81), substantial for the stifle joints (0.67), moderate for the metacarpophalangeal joint (0.59) with only fair agreement of the tarsal joints (0.30). Six osteochondral lesions were recorded on the second set of radiographs. There was overall substantial agreement between the ultrasonographic findings and the second set of radiographs. A second observer reviewed the ultrasonographic and radiographic images. There was moderate interobserver agreement comparing ultrasonographic images, and almost perfect interobserver agreement comparing radiographic images.Small number of horses who presented for yearling sale radiography for comparison. One ultrasonographer acquired all images, and two observers reviewed the images.Ultrasonographic screening of yearling horses with a relatively low number of lesions showed agreement with concurrent and yearling sale radiographs. [ABSTRACT FROM AUTHOR]

Copyright of Equine Veterinary Journal is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

BackgroundWarmblood Fragile Foal Syndrome Type 1 (WFFS) is an autosomal recessive disorder reported previously only in warmbloods and thought to be caused by a variant in the gene procollagen-lysine,2-oxoglutarate 5-dioxygenase 1 (PLOD1, c.2032G>A, p.Gly678Arg). Given the presentation of this Thoroughbred case, we hypothesised that a similar genetic mechanism caused this phenotype.ObjectivesTo describe the pathological and genetic findings on a foal presenting to a veterinary practice in the UK with skin lesions similar to other Ehlers-Danlos Syndromes, including those documented for warmbloods with WFFS.Study designA single case report describing a genetic investigation.MethodsA Thoroughbred foal presenting as dystocia was euthanised for multiple skin lesions and developmental abnormalities. DNA extracted from the foal was tested for the PLOD1 variant (c.2032G>A, p.Gly678Arg) using the commercially available assay. To confirm causality and further interrogate potential novel causes of Ehlers-Danlos Syndrome, 1799 functional candidate genes, including PLOD1, were analysed using whole genome sequencing data generated from DNA extracted from the foal's muscle. These data were compared to 34 control samples from at least 11 other breeds. Variants were prioritised for further evaluation based on predicted impact on protein function.ResultsPost-mortem evaluation concluded that this foal suffered from a condition of collagen dysplasia. The foal was homozygous for the c.2032G>A PLOD1 variant. Only two other missense variants identified from whole genome sequencing data were also computationally predicted to be deleterious to protein function, (NPHP3 c.1253T>C, p.Leu418Pro, EPDR1 c.154G>C, p.Glu52Gln). Neither of these genes have been linked to similar phenotypes, or Ehlers-Danlos Syndrome in humans or other species and thus further investigation of these variants as the cause of EDS was not warranted.Main limitationsThis study is a single case report in the Thoroughbred with no additional cases from this breed yet identified to replicate this finding.ConclusionsGiven the clinical presentation similar to WFFS, homozygosity for the PLOD1 variant, and absence of another more plausible causal variant from the WGS experiment, we conclude that PLOD1 c.2032G>A is the likely cause of this foal's condition. This is the first documented evidence of fragile foal syndrome caused by the PLOD1 variant in a breed outside of warmbloods, the Thoroughbred. We therefore recommend a change in the name of this disorder to fragile foal syndrome type 1 (FFS) and utilisation of genetic testing in Thoroughbreds to avoid producing affected foals.

Dental malocclusions are commonly encountered in horses. The objective of this study was to report the normal cephalometric values from skull computed tomography (CT) scans of adult Straight Egyptian Arabian (SEAR) and thoroughbred (TB) horses and to compare differences in the measurements between the two breeds. Standing skull CTs were performed on 29 clinically normal adult horses (15 SEAR; 14 TB) and cephalometric measurements were taken. All 9 cephalometric measurements, as well as the interincisal angle, were found to be significantly greater in TB than SEAR (P < 0.05). TB were found to have significantly greater facial line: mandibular length (FL/ML) ratios compared to SEAR (P = 0.002) whereas for the maxillary cheek teeth length: ethmoidal line ratio (Mxa/EtL), SEAR were found to have significantly greater values than TB (P = 0.0007). SEAR cephalometric measurements, as well as certain ratios, differ significantly from TB and could have an impact on the development of dental malocclusions in this breed. Further investigation is needed to ascertain whether these cephalometric differences between the two breeds predispose the SEAR to the development of dental malocclusions. [ABSTRACT FROM AUTHOR]

Copyright of Equine Veterinary Journal is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Simple Summary: The concept of altitude training became popular among human athletes following the 1968 Olympic Games, at which African runners were particularly successful. Culminating from these observations was the concept that during exercise training, local tissue hypoxia is an important adaptive stress for muscle that ultimately leads to superior physiological adaptations and enhanced endurance performance. The application of the concept of hypoxic training to the Thoroughbred horse is new, and now, with purpose-built hypoxic chambers, there has been a growing interest in its use in equine training programs. This paper provides a comprehensive discussion on the physiological impacts of hypoxic training, its benefits to endurance performance, and a rationale for utilizing it to improve performance in the equine athlete. All exercise-induced training adaptations are governed by genetics. Exercise prescriptions can be tailored to elicit the desired physiological adaptations. Although the application of hypoxic stimuli on its own is not ideal to promote favorable molecular responses, exercise training under hypoxic conditions provides an optimal environment for maximizing physiological adaptations to enhance endurance performance. The combination of exercise training and hypoxia increases the activity of the hypoxia-inducible factor (HIF) pathway compared to training under normoxic conditions. Hypoxia-inducible factor-1 alpha (HIF-1α) is known as a master regulator of the expression of genes since over 100 genes are responsive to HIF-1α. For instance, HIF-1-inducible genes include those critical to erythropoiesis, angiogenesis, glucose metabolism, mitochondrial biogenesis, and glucose transport, all of which are intergral in physiological adaptations for endurance performance. Further, hypoxic training could conceivably have a role in equine rehabilitation when high-impact training is contraindicated but a quality training stimulus is desired. This is achievable through purpose-built equine motorized treadmills inside commercial hypoxic chambers. [ABSTRACT FROM AUTHOR]

Behavioural plasticity enables horses entering an exercise training programme to adapt with reduced stress. We characterised SNPs associated with behaviour in yearling Thoroughbred horses using genomics analyses for two phenotypes: (1) handler‐assessed coping with early training events [coping] (n = 96); and (2) variation in salivary cortisol concentration at the first backing event [cortisol] (n = 34). Using RNA‐seq derived gene expression data for amygdala and hippocampus tissues from n = 2 Thoroughbred stallions, we refined the SNPs to those with functional relevance to behaviour by cross‐referencing to the 500 most highly expressed genes in each tissue. The SNPs of high significance (q < 0.01) were in proximity to genes (coping – GABARAP, NDM, OAZ1, RPS15A, SPARCL1, VAMP2; cortisol – CEBPA, COA3, DUSP1, HNRNPH1, RACK1) with biological functions in social behaviour, autism spectrum disorder, suicide, stress‐induced anxiety and depression, Alzheimer's disease, neurodevelopmental disorders, neuroinflammatory disease, fear‐induced behaviours and alcohol and cocaine addiction. The strongest association (q = 0.0002) was with NDN, a gene previously associated with temperament in cattle. This approach highlights functionally relevant genes in the behavioural adaptation of Thoroughbred horses that will contribute to the development of genetic markers to improve racehorse welfare. [ABSTRACT FROM AUTHOR]

Introduction: The social licence of the Australian thoroughbred (TB) industry relies on the general public's perception of how they manage the animal in their care. Method: This study examines the horse, race and activity records for the 37,704 horses racing and training in Australia from 1 August 2017 to 31 July 2018. Three‐quarters (75%, n = 28,184) of TBs started in one of the 180, 933 race starts that occurred during the 2017–2018 Australian racing season. Results: Horses participating in the 2017–2018 Australian racing season had a median age of 4 years, with geldings more likely to be aged 5 years and older. The majority of the TB racehorse population were geldings (51%, n = 19,210), with 44% (n = 16,617) females and only 5% (n = 1877) entire males. Horses aged 2 years were three times more likely to not start in a race in that year compared with older horses. At the end of the 2017–2018 racing season, 34% of the population had an inactive status recorded. Horses aged 2 years (median two starts) and 3 years (median five starts) had fewer starts than older horses (median seven starts). Eighty‐eight percent (n = 158,339) of race starts were over distances of 1700 metres or less. Race starts by horses aged 2 years (46%, 3264 of 7100) were more likely to have occurred at a metropolitan meeting compared with starts by older horses. Conclusion: This study provides a national overview of the racing and training activities and TBs participating in the 2017–2018 Australian racing season. [ABSTRACT FROM AUTHOR]

Background: Equine familial isolated hypoparathyroidism (EFIH) and fragile foal syndrome (FFS) are both fatal recessive conditions reported in Thoroughbred foals. The causal variants for EFIH (RAPGEF5 c.2624C>A; EquCab3.0. chr4: g.54108297G>T) and FFS (PLOD1 c.2032G>A; EquCab3.0, chr2: g.39927817) were recently reported. Prevalence assessment for these variants in a large cohort of samples is needed to provide evidence‐based recommendations for genetic testing. Objectives: To estimate the frequency of the EFIH and FFS variant alleles in the United States Thoroughbred population between 1988 and 2019, and determine whether these are recent mutations or are increasing in frequency due to current breeding practices. Study design: Population allele frequency study. Methods: Genomic DNA from hair and serum samples were genotyped for the EFIH and FFS. Allele frequencies between cohorts, based on year of birth (1988–2000, n = 728) and (2001–2019, n = 1059), as well as across the seven geographical regions of the United States were compared by Fisher's Exact tests. Results: EFIH and FFS allele frequencies were not significantly different between the two time points studied (0.008 and 0.004, respectively, in the older cohorts and 0.008 and 0.009 in most recent years). No EFIH or FFS homozygotes were detected. A sample from 1992 was identified as a carrier for EFIH and one from 1993 a carrier for FFS. Non‐significant changes in geographical distribution of carriers for both traits were observed. Main limitations: The earliest samples available for study were from foals born in 1988. Conclusions: The EFIH and FFS variants are present at low frequency in the United States Thoroughbred population but are not recent mutations. There is no evidence to support changes in allele frequency over time. However, given the closed studbook and breeding practices, continued monitoring of breed allele frequencies and genetic testing is recommended to avoid the mating of carriers and production of affected foals. [ABSTRACT FROM AUTHOR]

In the genomes of diploid organisms, runs of homozygosity (ROH), consecutive segments of homozygosity, are extended. ROH can be applied to evaluate the inbreeding situation of individuals without pedigree data and to detect selective signatures via ROH islands. We sequenced and analyzed data derived from the whole-genome sequencing of 97 horses, investigated the distribution of genome-wide ROH patterns, and calculated ROH-based inbreeding coefficients for 16 representative horse varieties from around the world. Our findings indicated that both ancient and recent inbreeding occurrences had varying degrees of impact on various horse breeds. However, recent inbreeding events were uncommon, particularly among indigenous horse breeds. Consequently, the ROH-based genomic inbreeding coefficient could aid in monitoring the level of inbreeding. Using the Thoroughbred population as a case study, we discovered 24 ROH islands containing 72 candidate genes associated with artificial selection traits. We found that the candidate genes in Thoroughbreds were involved in neurotransmission (CHRNA6, PRKN, and GRM1), muscle development (ADAMTS15 and QKI), positive regulation of heart rate and heart contraction (HEY2 and TRDN), regulation of insulin secretion (CACNA1S, KCNMB2, and KCNMB3), and spermatogenesis (JAM3, PACRG, and SPATA6L). Our findings provide insight into horse breed characteristics and future breeding strategies. [ABSTRACT FROM AUTHOR]

Significant research has focused on North American dirt and synthetic Thoroughbred racing surfaces. Turfgrass racing surfaces have received less consideration. Basic information, including climate and turfgrass species, can be documented relatively easily. However, a key characteristic, the particle size distribution of the growing medium, is not readily available for turf tracks. Particle size distribution and the deviation from nominal values are important to infiltration rate, shear strength, and turf health, as well as being critical for the selection of top-dressing and divot repair sand. The primary difficulty with obtaining the particle size distribution is the relatively large quantity of material required for traditional sedimentation test methods. Sampling an active racing surface could present a risk to the horses and riders. Laser diffraction testing methods present an opportunity to use much smaller samples. The use of smaller samples introduces new questions about the ability of a small sample to represent a large area, such as a racetrack. Tests were carried out with high resolution sampling at one racetrack. By sampling a large number of locations, 96 locations on a single racetrack, the variability of the track could be evaluated, and an eight-sample protocol was developed. Using the eight-location protocol, 22 additional turf racetracks throughout North America were sampled. A total of 23 turf racetracks were tested, representing all three of the designs used for North American turf racetracks. By looking at the three different track designs: engineered profile, engineered profile with fiber, and native soil, appropriate testing parameters and measurements were identified. While the primary objective was to understand turf racetracks, this unique data set also provided a method to investigate the applicability of laser diffraction for the analysis of soil samples. Mineralogy and organic content had previously been identified as important in the measurement of particle size distribution using laser diffraction. Mineralogy and organic content were determined for samples from each surface using X-ray diffraction (XRD) and loss on ignition. The PSD of the three types of turfgrass horse racing surfaces showed significant differences between native soil (N), engineered surfaces without synthetic fibers (EWOF), and engineered surfaces with synthetic fibers (EWF). These basic design descriptions were also found to be sufficient for making reasonable estimates of the settings used in the machine configuration and sample preparation. A single refractive index was used for the entire range of samples in this group; however, the sample quantity tested was different for the three different types of track designs. [ABSTRACT FROM AUTHOR]

Simple Summary: By using the Thoroughbred genome variant database to identify orthologues to personality-related human genes, we identified 18 potential personality-related genes in horses. These candidate genes have a total of 55 variants that cause amino acid substitutions when compared to the EquCab3.0 reference genome that may impact the function of the proteins encoded by these genes. Moreover, 15 of the 18 genes have not previously been linked to personality in horses, suggesting that this exploratory approach of related genes using human evidence can be useful for equine behavioral genetics. Although using this bioinformatics approach is less useful for investigating genes affecting personality in horses than it is in humans due to a lack of supporting personality research, this study highlights the potential for the identification of candidate genes. If future studies with equine behavioral datasets validate these potential personality–gene associations, this bioinformatics strategy may become important in the field of equine genetics. Considering the personality traits of racehorses (e.g., flightiness, anxiety, and affability) is considered essential to improve training efficiency and decrease accident frequency, especially when retraining for a second career that may involve contact with inexperienced personnel after retiring from racing. Studies on human personality-related genes are frequently conducted; however, such studies are rare in horses because a consistent methodology for personality evaluation is lacking. Using the recently published whole genome variant database of 101 Thoroughbred horses, we compared horse genes orthologous to human genes related to the Big Five personality traits, and identified 18 personality-related candidate genes in horses. These genes include 55 variants that involve non-synonymous substitutions that highly impact the encoded protein. Moreover, we evaluated the allele frequencies and functional impact on the proteins in terms of the difference in molecular weights and hydrophobicity levels between reference and altered amino acids. We identified 15 newly discovered genes that may affect equine personality, but their associations with personality are still unclear. Although more studies are required to compare genetic and behavioral information to validate this approach, it may be useful under limited conditions for personality evaluation. [ABSTRACT FROM AUTHOR]

Introduction: In recent years there has been public speculation about the breed, destination and number of horses being sold by public auction at livestock saleyards in Australia. Currently, there is little objective information available about the breed and condition of horses sold through this medium. With little publicly available objective data on these horses, the horse industry has been left vulnerable to misinformation. Accurate information regarding the composition and condition of horses attending saleyards is important to identify and address any welfare issues and to inform public debate. Method: Data were collected on 312 horses and ponies presented for sale through the Pakenham Horse Sales between July 2019 and March 2020. All horses and ponies were inspected at the saleyards and information on breed, age, body condition score (BCS), purchaser and sale price were recorded as the animals were auctioned. Results: Crossbred horses and ponies were the largest groups presented for sale. Ponies were more likely to be sold to private buyers. Quarter horses and riding ponies were as likely to be sent to slaughter as thoroughbreds and standardbreds. Entire males and females sold for lower prices than geldings. Most horses and ponies (64%) were sold to private buyers. More than three‐quarters (77%) of horses and ponies presented for sale had a BCS greater than or equal to three out of five. Conclusion: This pilot study challenges perceptions that thoroughbreds are the primary breed to attend public sales or that animals attending the sales are in poor condition. [ABSTRACT FROM AUTHOR]

This study is a part of an ample research concerning the genetic analysis (history) of Thoroughbred horses from Cislău studfarm. The genetic analysis studies are a part of Animal Genetic Resources Management because just start of them we elaborate the strategies for inbreeding management. This study has as purpose to present two important aspects of genetic analysis: reproductive isolation level and age structure.This parameters has a capital importance in animal breeding because there has a directly influence in animal population evolution. The reproductive isolation situation was quantified using the relation elaborated by S. Wright in 1921. The age structure situation is based on the age distribution histogram. The analysis showed that the Nonius horse from Izvin stud is a reproductively isolated population and have its own evolutionary path. Age structure is not balanced with negative repercurssions on generation interval.

The creation of genetically modified horses is prohibited in horse racing as it falls under the banner of gene doping. In this study, we developed a test to detect gene editing based on amplicon sequencing using next-generation sequencing (NGS). We designed 1012 amplicons to target 52 genes (481 exons) and 147 single-nucleotide variants (SNVs). NGS analyses showed that 97.7% of the targeted exons were sequenced to sufficient coverage (depth > 50) for calling variants. The targets of artificial editing were defined as homozygous alternative (HomoALT) and compound heterozygous alternative (ALT1/ALT2) insertion/deletion (INDEL) mutations in this study. Four models of gene editing (three homoALT with 1-bp insertions, one REF/ALT with 77-bp deletion) were constructed by editing the myostatin gene in horse fibroblasts using CRISPR/Cas9. The edited cells and 101 samples from thoroughbred horses were screened using the developed test, which was capable of identifying the three homoALT cells containing 1-bp insertions. Furthermore, 147 SNVs were investigated for their utility in confirming biological parentage. Of these, 120 SNVs were amenable to consistent and accurate genotyping. Surrogate (nonbiological) dams were excluded by 9.8 SNVs on average, indicating that the 120 SNV could be used to detect foals that have been produced by somatic cloning or embryo transfer, two practices that are prohibited in thoroughbred racing and breeding. These results indicate that gene-editing tests that include variant calling and SNV genotyping are useful to identify genetically modified racehorses. [ABSTRACT FROM AUTHOR]

Background: There is persistent concern among some trainers, owners and veterinarians regarding the effect of preoperative laryngeal function grade on the outcome of laryngoplasty and ventriculocordectomy (LPVC). Objectives: To determine the effect of laryngeal function grade prior to LPVC on postoperative performance. Study design: Retrospective case‐series. Methods: Medical and race records of Thoroughbred racehorses diagnosed with recurrent laryngeal neuropathy (RLN) and treated with LPVC between 1998 and 2013 were reviewed. Horses were placed into three groups based on preoperative laryngeal function grade (grade III.1, grades III.2/III.3, and grade IV). The effect of preoperative laryngeal function grade on postoperative performance was determined by multivariable logistic regression, Cox proportional hazard model and multivariable linear regression analysis. Results: In a multivariable logistic regression, grade III.2/III.3 horses had 1.88 times higher odds (95% CI = 1.03‐3.43) of racing after LPVC than grade IV (P =.04). A multivariable Cox's proportional hazard analysis controlling for race prior to surgery (P <.01) showed that likelihood of racing postoperatively was not different between grade III.1 and grade IV (P =.6), and although not statistically significant, there was a tendency for grades III.2/III.3 to be more likely to race postoperatively than horses with grade IV (P =.07). Kaplan–Meier survival analysis showed that grade IV horses took a longer time to race compared with grade III.1 and grade III.2/III.3. Laryngeal function grade did not influence the mean earnings per start. Main limitations: The small number of horses in the grade III.1 group compared with the III.2/III.3 and IV groups influenced the effect of grade III.1 on outcome. Conclusions: Laryngeal function grade may affect likelihood of racing after LPVC, but not earnings per start. Grade III. 2/III.3 horses were more likely to race postoperatively than grade IV horses, and grade IV horses took a longer time to first race after LPVC. [ABSTRACT FROM AUTHOR]

Population demographics and reproductive performance of Thoroughbred populations have been described, but the most recent assessment of the South African Thoroughbred population was reported two decades ago. Objectives of this study were to report demographic data for selected Thoroughbred breeding populations and to analyse selected mare-level variables in association with foaling outcomes, as predictors of reproductive performance. The National Horseracing Authority of Southern Africa’s stud health scheme requires annual screening of Thoroughbred stallions, maiden and barren mares for venereal pathogens prior to breeding. In 2018 and 2019, 1 065 and 1 207 horses were sampled, respectively. Demographic data were sourced from laboratory sample submission forms that accompanied samples and supplemented by data gathered from the annual Thoroughbred foal identification programme. Univariate analysis of candidate predictors of successful foaling outcomes was performed followed by assessment in a multivariable model. Median ages of mares and stallions tested in 2018 and 2019 were nine and 11 years, respectively. Nearly twice the number of barren compared to maiden mares were tested in each year, and failure to conceive was the most common reported reason for classification as barren. Of mares tested in 2018 and 2019, 68.1% (95% CI 65.1–70.9) and 63.3% (95% CI 60.4–66.1), respectively, subsequently produced foals that were presented for identification. Mare age, rather than reproductive status, was a significant predictor of having a foal presented for identification. In conclusion, novel demographic data were described for South African Thoroughbred populations. Seasonal foaling rate as the selected measure of reproductive performance for sampled mares ranged from 63.3% to 68.1% and declined with increasing mare age. [ABSTRACT FROM AUTHOR]

In the genomes of diploid organisms, runs of homozygosity (ROH), consecutive segments of homozygosity, are extended. ROH can be applied to evaluate the inbreeding situation of individuals without pedigree data and to detect selective signatures via ROH islands. We sequenced and analyzed data derived from the whole-genome sequencing of 97 horses, investigated the distribution of genome-wide ROH patterns, and calculated ROH-based inbreeding coefficients for 16 representative horse varieties from around the world. Our findings indicated that both ancient and recent inbreeding occurrences had varying degrees of impact on various horse breeds. However, recent inbreeding events were uncommon, particularly among indigenous horse breeds. Consequently, the ROH-based genomic inbreeding coefficient could aid in monitoring the level of inbreeding. Using the Thoroughbred population as a case study, we discovered 24 ROH islands containing 72 candidate genes associated with artificial selection traits. We found that the candidate genes in Thoroughbreds were involved in neurotransmission (CHRNA6, PRKN, and GRM1), muscle development (ADAMTS15 and QKI), positive regulation of heart rate and heart contraction (HEY2 and TRDN), regulation of insulin secretion (CACNA1S, KCNMB2, and KCNMB3), and spermatogenesis (JAM3, PACRG, and SPATA6L). Our findings provide insight into horse breed characteristics and future breeding strategies.

Considering the personality traits of racehorses (e.g., flightiness, anxiety, and affability) is considered essential to improve training efficiency and decrease accident frequency, especially when retraining for a second career that may involve contact with inexperienced personnel after retiring from racing. Studies on human personality-related genes are frequently conducted; however, such studies are rare in horses because a consistent methodology for personality evaluation is lacking. Using the recently published whole genome variant database of 101 Thoroughbred horses, we compared horse genes orthologous to human genes related to the Big Five personality traits, and identified 18 personality-related candidate genes in horses. These genes include 55 variants that involve non-synonymous substitutions that highly impact the encoded protein. Moreover, we evaluated the allele frequencies and functional impact on the proteins in terms of the difference in molecular weights and hydrophobicity levels between reference and altered amino acids. We identified 15 newly discovered genes that may affect equine personality, but their associations with personality are still unclear. Although more studies are required to compare genetic and behavioral information to validate this approach, it may be useful under limited conditions for personality evaluation.

The proportion of Thoroughbred (TB) horses that commence training and eventually race, is an important industry‐level indicator of how successful it is at producing horses suitable for racing. It is also of interest to the wider community and is central to the issue of whether there is overbreeding in the Australian TB industry. This study investigated the training and racing records for the 2005 and 2010 Victorian TB foal crops to determine the proportion of TBs that train and race, and the age of entering training and first race start. Subsets of the foal crop were also examined to determine if premier yearling sale cohorts would produce selection bias. The Australian Stud Book (ASB) registered 7662 TB horses born in Victoria in 2005 (n = 4116) and 2010 (n = 3546). Of these, 5614 (73%) entered training and 4868 (64%) started in at least one race. Fourteen percent (n = 1045) of the study cohort had their first race start as 2‐year‐olds and 35% (n = 2644) had their first start as 3‐year‐olds. A higher proportion of TB horses that attended premier yearling sales entered training (93%) and raced (84%). This study established a baseline for training and racing milestones, such as the proportion and age that horses commenced training, and age of first start using population‐level data. It also established that the use of subsets of the population can introduce selection bias. [ABSTRACT FROM AUTHOR]

The aim of the research was to monitor current trends in international show jumping and assess how the proportion of Thoroughbred blood in the pedigree of horses, age, breed, sex and sport season influenced the competition results of show-jumping horses at the world level. The research was based on the databases of jumping rankings for the years 2010, 2014 and 2018 published by the International Federation for Equestrian Sports (FEI). All horses from the FEI rankings were included in the database with the exception of ponies and also horses lacking basic data. This yielded a total of 14,980 horses. The rankings of horses were calculated according to FEI methodology on the basis of the best 30 results every year in international show-jumping competitions with a minimum fence height of 1.45 m. The most represented breed was the Dutch Warmblood (19.26%) and the most common sex was gelding (43.98%). Since 2010 the standard proportion of Thoroughbred blood in the pedigrees of show-jumping horses has decreased and in 2018 the average proportion of Thoroughbred in the pedigree was 41.61%. The analysis of the statistics in the whole database established a significant (P ˂ 0.01) influence of all observed factors. The horses achieved a statistically higher ranking in 2018 (117.57) than in 2010 (98.33) and 2014 (105.93). The groups with a proportion of Thoroughbred between 30.10 and 70.00% achieved a significantly higher ranking than horses with a zero proportion of Thoroughbred in the pedigree. Stallions achieved a significantly higher ranking (117.84 points) compared to geldings (105.76 points) and mares (104.66 points). The horses aged 10–13 years old achieved better results (124.71 points) than the younger group of horses (76.66 points) and older group of horses (109.29 points, P = 0.0033). Statistically conclusive differences were found between AES horses (162.81 points) and the group of non-sport horse breeds (68.26 points) and also between AES horses and horses of unknown pedigree (38.61 points). There were no significant differences between the principal warmblood sport breeds produced in Europe. [ABSTRACT FROM AUTHOR]

Background: High‐serum γ‐Glutamyl Transferase (GGT) activity has been associated with and thought to be a marker of maladaptation to training and possibly poor performance in racehorses, but the cause is unknown. Objectives: To investigate possible metabolic and infectious causes for the high GGT syndrome. Study design: Pilot case‐control study and nested case‐control study. Methods: The case‐control study in 2017 included 16 horses (8 cases and 8 controls with median [range] serum GGT 82 [74‐148] and 22 [19‐28] IU/L, respectively) from the same stable. In 2018, similar testing was performed in a nested case‐control study that identified 27 case (serum GGT 50 ≥ IU/L)‐control pairs from three stables for further testing. Serum liver chemistries, selenium measurements, viral PCR and metabolomics were performed. Results: No differences were found in frequency of detection of viral RNA/DNA or copy numbers for equine hepacivirus (EqHV) and parvovirus‐hepatitis (EqPV‐H) between cases and controls. Mild increases in hepatocellular injury and cholestatic markers in case vs control horses suggested a degree of liver disease in a subset of cases. Metabolomic and individual bile acid testing showed differences in cases compared with controls, including increased abundance of pyroglutamic acid and taurine‐conjugated bile acids, and reduced abundance of Vitamin B6. Selenium concentrations, although within or above the reference intervals, were also lower in case horses in both studies. Main limitations: Observational study design did not allow us to make causal inferences. Conclusions: We conclude that high GGT syndrome is likely a complex metabolic disorder and that viral hepatitis was not identified as a cause for this syndrome in this cohort of racehorses. Our results support a contribution of oxidative stress and cholestasis in its pathophysiology. [ABSTRACT FROM AUTHOR]

Background: Proximal sesamoid bone fractures are common catastrophic injuries in racehorses. Understanding the response of proximal sesamoid bones to race training can inform fracture prevention strategies. Objectives: To describe proximal sesamoid bone microstructure of racehorses and to investigate the associations between microstructure and racing histories. Study design: Cross‐sectional. Methods: Proximal sesamoid bones from 63 Thoroughbred racehorses were imaged using micro‐computed tomography. Bone volume fraction (BVTV) and bone material density (BMD) of the whole bone and four regions (apical, midbody dorsal, midbody palmar and basilar) were determined. Generalised linear regression models were used to identify the associations between bone parameters and race histories of the horses. Results: The mean sesamoid BVTV was 0.79 ± 0.08 and BMD was 806.02 ± 24.66 mg HA/ccm. BVTV was greater in medial sesamoids compared with lateral sesamoids (0.80 ± 0.07 vs 0.79 ± 0.08; P <.001) predominantly due to differences in the apical region (medial—0.76 ± 0.08 vs lateral—0.72 ± 0.07; P <.001). BVTV in the midbody dorsal region (0.86 ± 0.06) was greater than other regions (midbody palmar—0.79 ± 0.07, basilar—0.78 ± 0.06 and apical—0.74 ± 0.08; P <.001). BVTV was greater in sesamoids with more microcracks on their articular surface (Coef. 0.005; 95% CI 0.001, 0.009; P =.01), greater extent of bone resorption on their abaxial surface (Grade 2—0.82 ± 0.05 vs Grade 1—0.80 ± 0.05 or Grade 0—0.79 ± 0.06; P =.006), in horses with a low (0.82 ± 0.07) or mid handicap rating (0.78 ± 0.08) compared with high rating (0.76 ± 0.07; P <.001), in 2‐ to 5‐year‐old horses (0.81 ± 0.07) compared with younger (0.68 ± 0.08) or older horses (0.77 ± 0.08; P <.001) and in horses that commenced their racing career at less than 4 years of age (0.79 ± 0.08 vs 0.77 ± 0.77; P <.001). BMD was greater in the midbody dorsal (828.6 ± 19.6 mg HA/ccm) compared with other regions (apical—805.8 ± 21.8, midbody palmar—804.7 ± 18.4 and basilar—785.0 ± 17.1; P <.001), in horses with a handicap rating (low—812.1 ± 20.0, mid—821.8 ± 21.3 and high—814.6 ± 19.4) compared with those with no rating (791.08 ± 24.4, P <.001), in females (806.7 ± 22.0) and geldings (812.2 ± 22.4) compared with entires (792.7 ± 26.2; P =.02) and in older horses (<2‐year‐old—763.7 ± 24.8 vs 2‐ to 5‐year‐old—802.7 ± 23.4, and 6‐ to 12‐year‐old—817.8 ± 20.0; P =.002). Main limitations: Data were cross‐sectional. Conclusions: Densification of the proximal sesamoid bones is associated with the commencement of racing in younger horses and the presence of bone fatigue‐related pathology. Lower sesamoid BVTV was associated with longevity and better performance. [ABSTRACT FROM AUTHOR]

Tongue‐ties (TTs) are used to aid control and aim to conservatively treat upper airway disorders in racehorses. However, welfare concerns have led to their use being banned in other equestrian disciplines. In the United Kingdom, TTs have been reported to be used in approximately 5% of starts. The frequency of their use elsewhere is unknown. The objectives of this retrospective single cohort study were to estimate the frequency of TT use within the Australian Thoroughbred (TB) racing industry, and to describe usage patterns. Data of all Australian TB horse races from 2010 to 2013 calendar years were collected by accessing the Racing Information Services Australia database. Frequency of TT use was calculated, and usage patterns were explored at the start, horse and trainer levels. Between 2010 and 2013, there were a total of 728,678 starts from 62,377 horses prepared by 4927 trainers and that raced on 1453 race dates across 402 venues. Tongue‐ties were used in 21.4% of starts; however, frequency varied according to location, race, trainer and horse. At the horse level, 32.2% wore a TT at least once and 7.6% wore it at every race on record. At the trainer level, 71.3% used TTs in at least one of their horses but only 1.4% used them systematically. The present study concludes that TT use in Australian TB racehorses, during the period 2010–2013, was common and considerably higher than previously reported in the United Kingdom. Most Australian trainers use the device and appear to adapt its usage according to individual horse and race factors. [ABSTRACT FROM AUTHOR]

The creation of genetically modified horses is prohibited in horse racing as it falls under the banner of gene doping. In this study, we developed a test to detect gene editing based on amplicon sequencing using next-generation sequencing (NGS). We designed 1012 amplicons to target 52 genes (481 exons) and 147 single-nucleotide variants (SNVs). NGS analyses showed that 97.7% of the targeted exons were sequenced to sufficient coverage (depth > 50) for calling variants. The targets of artificial editing were defined as homozygous alternative (HomoALT) and compound heterozygous alternative (ALT1/ALT2) insertion/deletion (INDEL) mutations in this study. Four models of gene editing (three homoALT with 1-bp insertions, one REF/ALT with 77-bp deletion) were constructed by editing the myostatin gene in horse fibroblasts using CRISPR/Cas9. The edited cells and 101 samples from thoroughbred horses were screened using the developed test, which was capable of identifying the three homoALT cells containing 1-bp insertions. Furthermore, 147 SNVs were investigated for their utility in confirming biological parentage. Of these, 120 SNVs were amenable to consistent and accurate genotyping. Surrogate (nonbiological) dams were excluded by 9.8 SNVs on average, indicating that the 120 SNV could be used to detect foals that have been produced by somatic cloning or embryo transfer, two practices that are prohibited in thoroughbred racing and breeding. These results indicate that gene-editing tests that include variant calling and SNV genotyping are useful to identify genetically modified racehorses.

Background: Racehorses are at an increased risk of stress fracture within the first 12 months of racing and when resuming training after a break. Research in these high‐risk periods and on the effect of performance post‐recovery is limited. Objectives: To describe the occurrence of stress fractures, diagnosed by nuclear scintigraphy (NS), in racehorses' first 12 months training in Hong Kong, and their impact on racing performance and career length. Study design: Retrospective 1:2 matched case‐control study. Methods: Clinical records of horses with NS‐diagnosed stress fractures within 365 days of import between 2006 and 2018 were collated. Cases and controls were matched on import date. Univariable conditional logistic regression compared signallment, pre‐fracture training and post‐recovery racing performance between cases and matched controls. Shared Frailty Cox regression analysed time from import to fracture and total career length. Results: Eighty‐seven horses sustained a NS‐diagnosed fracture within their first year in Hong Kong (incidence risk 1.7% [95% confidence interval (CI) 1.4%‐2.1%; N = 5180]). The humerus (42.0%; 95% CI 31.8%‐52.6%; n = 39) and tibia (28.0%; 95% CI 19.1%‐38.2%; n = 26) were the most common stress fracture sites. Cases missed a median of 63 days (Interquartile range (IQR) 49‐82) of training because of fracture. Within the 12 months following diagnosis, case horses had a median of four (IQR 2‐4, P <.0001) fewer race starts and were down HK$ 206 188 (IQR HK$ 0‐436 800, P =.007) in race earnings compared to controls. Career length did not significantly differ between cases and controls (median 2 years and 3 months; IQR 15.3‐39.1 months; P =.2). Main limitations: Only stress fractures diagnosed by NS were included, hence, the study is not representative of all stress fractures occurring in racehorses in Hong Kong. Conclusions: Racehorses sustaining a stress fracture within 1 year of entering Hong Kong lost significant time in training, earnings and race starts. However, overall career length was unaffected. [ABSTRACT FROM AUTHOR]

The Thoroughbred (TB) horse is the best racehorse breed used in the racing industry. This breed has had a closed studbook for about 300 years. In Russia TB horses have been bred since the second half of the XVIII century. The modern Russian Stud Book register of TB horses is partially presented by stallions and broodmares imported from different countries. The genealogical structure of the breed is represented by 17 lines, among which the Northern Dancer line dominates (30.9 %). The study of features of different lines of TB was carried out on 17 loci of DNA microsatellites (VHL20, HTG4, AHT4, HMS7, HTG6, AHT5, HMS6, ASB23, ASB2, HTG10, HTG7, HMS3, HMS2, ASB17, LEX3, HMS1 and CA425) to assess genetic differentiation of the genealogical structure. The results of the DNA typing of 8091 Thoroughbred horses across microsatellite loci show that the gene pool of the domestic population is represented by 100 alleles typical of the breed. A comparative analysis of the genotypes of horses representing different lines indicates that they differ in the number of alleles (85–99), allele frequencies, the level of polymorphism Ae (2.93–3.48) and the degree of the observed heterozygosity Ho (0.653–0.739). The genetic distances between the lines varied in a wide range from 0.014 (Nasrullah – Northern Dancer) to 0.125 (Massine – Teddy). The correspondence to HWE was maintained in most lines, which is confirmed by the negative values of Fis. Cluster analysis demonstrated the correspondence of the obtained dendrogram of Nei’s genetic distances to its genealogical scheme of lines. Genetic differentiation of lines by index Fst varied in a range 0.005–0.073 at the mean value Fst = 0.024. The data indicate genetic differentiation of lines of TB at the STR markers and confirm the effectiveness of the system of linear breeding for the maintenance of interbreed biodiversity.

Abstract Objective According to oral traditions of horse caretakers and trainers, the differences in the position and number of facial hair whorls may be associated with temperamental traits. Elucidating genetic background of facial hair whorls and its relationship to temperamental traits may promote more efficient breeding and maintenance of racehorses. In this study, we estimated heritabilities of the position and number of facial hair whorls in Japanese Thoroughbred horses. Results The number of facial hair whorls varied from one to four and heritability estimate in 4024 Thoroughbred horses was low (h 2= 0.160). The positions of facial hair whorls were categorized into high, medium, and low, based on their locations. This trait was estimated to have high heritability (h 2= 0.643) in 3782 Thoroughbred horses. These results indicated that a larger proportion of the variation in the studied population was due to genetic factors for facial hair whorls position. Because a similar result was also observed in another horse breed, Polish Konik horses, high heritability of facial hair whorl position may be characteristic of multiple horse breeds. We expect that these results will stimulate future studies to elucidate the relationship among temperamental traits and facial hair whorls in all horse breeds.

During the past 20 years, there has been a contraction in the New Zealand Thoroughbred industry and, to a lesser extent, within the Standardbred industry. These changes have seen an increasing proportion of the market being associated with fewer larger commercial farms. Many of these farms manage their own mares, and the mares and foals of several clients. This, in turn, has increased the similarity of the management of breeding and young stock within New Zealand. The temperate climate allows the majority of the management of breeding and young stock to be pasture based. The predominant pasture is ryegrass-clover mix that has been demonstrated to provide adequate nutrition for growth and development. The temperate climate also permits management of horses at pasture year round, which is proposed to stimulate development of the musculoskeletal system. Apart from a brief period during weaning, most young stock remain at pasture from birth until the start of yearling preparation. Free access to pasture exercise provides the opportunity to stimulate the musculoskeletal system for the future challenges as a racehorse. The export focus of many of the equine industries heavily influences the management decisions. Despite the availability of good-quality pasture post-weaning, many foals receive up to 50% of the daily dietary energy requirement as concentrates, possibly reflecting the emphasis on early sales as yearlings and the drive to optimise growth. The observations of drench resistance of common internal parasites presents an emerging problem for pasture-based production systems. Alarge proportion of the Thoroughbred foal crop is exported as yearlings or ready to run 2-year-olds. There is an increasing trend for Standardbreds to be sold as yearlings and this has resulted in changes in the management of Standardbred young stock. [ABSTRACT FROM AUTHOR]

The Thoroughbred and Standardbred studbooks are the largest in New Zealand, where the production of horses is pasture based. Each racing studbook is closed, and both have well structured systems in place for recording breeding data. There are significant pressures on the Thoroughbred and Standardbred breeding industries with declining broodmare numbers, and increasingly large book sizes for popular stallions. The breeding season for Thoroughbreds is very short, with disparity between the official breeding season and the physiologic breeding season for mares. These issues are confounded by variable gestation lengths of mares, making it difficult for mares to maintain yearly foaling patterns. However, the reproductive efficiency of Thoroughbred mares is improving, mainly due to veterinary and stud management practices such as those to ensure that dry mares are cycling at the start of the breeding season, foaling mares are bred on foal heat, and that mares are kept in good body condition at breeding. There is also a bias towards breeding younger mares with high fertility in preference to older mares, unless they have desired genetics or successful offspring. Careful management of popular Thoroughbred stallions ensures that large books of mares can be covered by natural service. In contrast, Standardbred stallions are collected every-other-day using an artificial vagina, allowing the breeding of mares at distant locations by artificial insemination, using chilled or frozen semen. Breeding horses kept at pasture under New Zealand conditions requires excellent stud management and veterinary management to achieve good outcomes. [ABSTRACT FROM AUTHOR]

The present review examines the commercial production of racing and sport horses inNewZealand, describing the size and scope of the industries, the management and feeding, and the training and wastage of race (Thoroughbred and Standardbred) and sport horses. The number of horses per head of population in New Zealand (30/1000 people) is high by international standards and the main equine industries generate~2%of national gross domestic product. InNewZealand the Thoroughbred breeding and racing industry dominates organised equestrian activity (economically and numerically). Furthermore, this Thoroughbred bias has an influence on equestrian culture and may explain, in part, the high proportion of Thoroughbred sport horses registered for eventing in New Zealand, which is in contrast to other international sport-horse populations. An understanding of the production, management and structure of the racing and sport industries in NewZealand is paramount to ensure the health and welfare of the equine athlete and the continuing success of the industries. [ABSTRACT FROM AUTHOR]

The aim of this study was to test the hypothesis that Thoroughbred (TB) ancestors blood percentage in a pedigree is a potential factor differentiating the level of fearfulness (based on behavior and heart rate (HR)) and performance scores in warmblood stallions. A total of 267 three-year-old warmblood stallions were subjected to the novel-object based test during their participation in the performance tests’ program. The effect of ancestors percentage contribution in the pedigree was analyzed by taking into account horses of four TB (75.00%) ancestor groups. It was found that the stallions with a higher proportion (>75.00%) of TB blood revealed higher values of HR measured at the riding hall just before the start of the fearfulness test. The results showed that the higher proportions of TB ancestors blood in the stallions’ pedigree were correlated with the higher values for total time to pass novel objects when led by a handler during the fearfulness test. Negative correlations were found between the TB percentage and the scores for character and trot evaluated by the trainer as well as rideability evaluated by the test rider. The fi ndings imply that a high proportion of Thoroughbreds in the pedigree may negatively infl uence some performance traits and increase fear reactivity in warmblood stallions.

Background: Many racing jurisdictions monitor race‐day musculoskeletal injury (MSI) but fail to evaluate injuries occurring during training. Additionally, previous risk factor analyses have failed to explore temporal trends in injury occurrence. Objectives: To use time‐series analysis techniques to identify trends, cyclicity and peaks in MSI incidence, in racehorses training and racing at the Hong Kong Jockey Club (HKJC) from July 2010 to June 2018. Study design: Retrospective longitudinal study. Methods: The monthly incidence of all MSI, superficial digital flexor tendon (SDFT) injury, suspensory ligament injury and appendicular skeletal fracture occurring in training and racing were collected from veterinary records. The number of horses in training was collated monthly from trainer records. Time‐series analysis techniques were used to describe trends and cyclical patterns for injury types. For each injury, incidence risks above the 90th percentile were identified as peaks in incidence. Results: A total of 1471 injuries were recorded over eight racing seasons; 605 fractures (41.1%), 550 SDFT injuries (37.4%), and 316 suspensory ligament injuries (21.5%). Evidence of seasonality was detected in fracture incidence risk; increasing from October (median 0.25 per 1000 horses) until May (median 0.71 per 1000 horses), coinciding with the racing season (ending mid‐July). Elevated incidence of MSI occurred throughout 2012; however, the greatest incidence risks of SDFT (14.8 per 1000 horses) and fracture (1.3 per 1000 horses) occurred since 2017. Main limitations: Monthly (opposed to daily) incidence risk of injury reduced the resolution of the data. Additionally, fracture was not described according to bone or fracture type, which may have confounded overall trends. Conclusions: Evidence for seasonal variation in the incidence of fracture occurrence has been demonstrated. Based on using time‐series techniques, further epidemiological studies, retrospectively targeting periods of high peaks in injury incidence risk could be used to aid identification of risk factors for injury. [ABSTRACT FROM AUTHOR]

Summary: Thousands of Thoroughbred horses retire from racing each year and go on to second careers unrelated to racing. Although there are many publications regarding health concerns for Thoroughbreds while racing, evidence‐based information regarding what happens after retirement from racing is scarce. Veterinarians are relegated to use anecdotal information to guide owners and potential owners. The study objective was to collect and evaluate extensive information regarding the use and perceived health of Thoroughbreds retired from racing, as well as owner satisfaction. A 31‐question survey on use, health and behaviour was made available to owners of Thoroughbred horses who had retired from racing. A similar survey was available to owners of non‐Thoroughbred horses for a control population. Racing data were obtained from a publicly available database for Thoroughbreds. Statistical analysis was performed to compare incidence of health and behaviour issues between Thoroughbreds and controls and between different racing experiences for Thoroughbreds. Thoroughbreds retired from racing were more likely to suffer from musculoskeletal injuries, gastrointestinal, behavioural and foot/hoof issues than controls. Age at first start, age at last start, number of starts and breaks of 6 months or more during racing career did not affect incidence of musculoskeletal disease, behavioural issues, hoof/foot issues, respiratory disease and neurologic disease. Horses with >51 lifetime starts were more likely to experience gastrointestinal disease in the first year after retirement from racing. Thoroughbreds were as likely as controls to have eventual resolution of issues present at acquisition. Veterinarians can use this information to guide pre‐purchase evaluations, provide ongoing care and counsel owners/prospective owners on the possible needs of Thoroughbred horses retired from racing. Knowing the common issues faced by the population will increase the success of transition from racing by creating informed veterinarians and owner expectations. [ABSTRACT FROM AUTHOR]

Background: Equine influenza (EI) outbreaks occurred among horses on four racing yards (two National Hunt, one Flat, one mixed National Hunt racing/breeding yard) in Ireland within a 4‐week period. Objectives: To carry out a detailed analysis of racing yards affected in order to identify the source of infection and monitor virus spread among a vaccinated population. Study design: Observational field study. Methods: Epidemiological and vaccination data along with repeat clinical samples were collected from 118 horses on four premises. Results: Failure to implement appropriate biosecurity measures following the introduction of new arrivals and the return of horses from equestrian events contributed to disease spread as did the movement of horses within premises. Mixing of racing and non‐racing populations with inadequate vaccination histories also facilitated virus transmission. The index case(s) on all premises was vaccinated in accordance with the Turf Club rules. Vaccine breakdown was observed across all products in 27/80 horses (33.8%) with an up‐to‐date vaccination record. Eighteen of the 27 (66.7%) horses had not received a booster vaccination within the previous 6 months and 10 (37%) horses were due annual booster vaccination at the time of developing clinical signs. Main limitations: The interpretation of laboratory results followed a delay in veterinary intervention. Conclusions: Annual booster vaccination should not be relied on as the sole preventative measure against EI. The findings of this study suggest that increasing the frequency of booster vaccinations may be beneficial particularly in young horses and that synchronised scheduling of vaccination regimes across racing yards may contribute to high‐risk periods for EI virus (EIV) transmission. [ABSTRACT FROM AUTHOR]

Summary: The radiographic appearance of the stifle of young horse changes during the first 18 months of life but is not well described in Thoroughbreds. Our objective was to describe the radiographic appearance of the Thoroughbred stifle from 5 to 18 months of age and determine whether limiting exercise impacts the prevalence of radiographic abnormalities (RA). Bilateral stifle radiographs were obtained at a mean of 161 days of age in 141 subjects (set 1) and 347 days (set 2), and in 114 available subjects at 534 days (set 3), and graded for RA of the trochlear ridges (TR) and medial femoral condyle (MFC). The impact of exercise limits on RA was determined from a subgroup of subjects with set 1 RA that had 30–90 days limited exercise. Stifle RA were present in 50 subjects (35%) at set 1: 39 TR and 11 MFC. At set 2, 24 subjects (15.6%) had RA: 13 TR and 11 MFC. Set 1 RA had resolved in 36 (72%) subjects, persisted in 11 (22%) and changed location in 3. Ten of 91 (11%) subjects developed new RA at set 2. Twenty‐seven subjects were unavailable for set 3 imaging, 6 with LTR RA at set 2. At set 3, 12/114 (11%) subjects had RA: 5 TR and 7 MFC. Set 2 RA resolved in 9 (50%) subjects, persisted in 8 (44%), and changed location in one. Three of 96 subjects developed new RA at set 3. Radiographic abnormality prevalence at set 3 was not different after limiting exercise. It was concluded that RA in the TR and MFC are common in 6‐month‐old Thoroughbreds and often resolve by 18 months. Radiographic abnormalities that develop later (~12 months of age) are less likely to resolve. [ABSTRACT FROM AUTHOR]

Summary: A quarter crack is a defect of the hoof wall that is caused by a combination of factors that affect the quality of the hoof horn. To date, no peer‐reviewed studies have described the incidence of quarter cracks in Thoroughbred racehorses during training. Further, there is limited information regarding the clinical presentation and racing performance following a quarter crack. Therefore, the objectives of the current study were to describe the incidence, clinical presentation and outcome of quarter cracks sustained by horses in racing and training at the Hong Kong Jockey Club. Horses with quarter cracks that required attention from a farrier and/or veterinarian were identified using farrier and veterinary clinical records. Data were described, including the affected foot, presence of lameness, treatment, reoccurrence and racing data for case and control horses. There was no significant difference between case and control horses for total career length, and the total number of starts, wins and places. Seventy‐four horses experienced at least one quarter crack during the study period, for a total of 114 quarter cracks. Half of the horses experiencing a quarter crack were not lame on presentation. Most quarter cracks occurred in the right fore (n = 56/102; 54.9%) and in a medial position (n = 90/102; 88.2%). Horses returned to racing a median of 50 days after the first treatment, for a median of 18 starts. Six horses retired due to the occurrence of a quarter crack. Although the incidence of quarter cracks in racehorses is low and the majority of horses returned to a racing career comparable to unaffected horses, the reoccurrence rate is high, putting an emphasis on ongoing hoof management and farrier care to help prevent the reoccurrence. [ABSTRACT FROM AUTHOR]

Summary: Regular monitoring of movement asymmetry with inertial measurement units (IMUs) to aid in the diagnosis of the underlying cause of a lameness is feasible. Normal ranges for specific groups of horses may be required, with consideration of expert veterinary opinions for both asymmetry screening and lameness assessment. The aim of this study was to determine movement asymmetry values compared with expert lameness scores to enable screening for lameness in Thoroughbreds in race training. IMU gait assessment during in‐hand trot‐up was performed in 25 racehorses undergoing routine gait analysis or lameness examination at the Singapore Turf Club. Video recordings were graded numerically (0–5) for lameness by six experienced racehorse veterinarians. Inter‐observer agreement and consistency were determined. Median lameness scores were used to calculate sensitivity and specificity for head, withers and pelvic movement asymmetry. Guideline values for aligning movement asymmetry values with expert opinions about forelimb and hindlimb lameness were determined from receiver operating characteristics (ROC). Inter‐observer agreement was poor to fair, inter‐observer consistency was good (intraclass correlation coefficient: 0.667 for forelimbs and 0.617 for hindlimbs). ROCs indicated higher discriminative power for hindlimb lameness using pelvic asymmetry (90% sensitivity, 93% specificity) compared with forelimb lameness using head asymmetry (69% sensitivity, 89% specificity) or withers asymmetry (44% sensitivity, 89% specificity). When compared to expert lameness scores from videos of a limited number of Thoroughbred racehorses, preliminary guideline values for movement asymmetry screening for forelimb lameness (>|14.5 mm|) and hindlimb lameness (>|7.5 mm|) are higher than previously reported clinical thresholds of >|7 mm| for head movement and >|4 mm| for pelvic movement asymmetry. [ABSTRACT FROM AUTHOR]

Summary: Background: Slab fractures of the third carpal bone (C3) are a common injury of Thoroughbred racehorses. Results of arthroscopically guided repair have not been reported since the initial description of the technique in 1986. Additionally, fracture details and racing outcomes in a population of Thoroughbreds racing under UK jurisdiction have not previously been described. Objectives: To report the frequency distribution of C3 slab fractures and to determine the impact on racing performance following arthroscopically guided repair in a population of Thoroughbred racehorses. Study design: Retrospective case series. Methods: Case records of Thoroughbred racehorses undergoing arthroscopically guided repair of C3 slab fractures at Newmarket Equine Hospital between 2006 and 2015 were retrieved. Radiographs and arthroscopic studies were reviewed. The effect of demography and fracture morphology on racing outcome was evaluated. Results: C3 slab fractures occurred most commonly through the radial facet in a frontal plane (45/71 63.4%). Comminution was identified during arthroscopy in 42/71 (59.2%) fractures and occurred most frequently at the palmar margin of the fracture. Forty‐one out of 65 horses (63.1%) raced at least once post‐operatively. Females were less likely to return to racing compared to males (P<0.001). Horses that had raced before injury were more likely (OR 4.4, 95% CI 1.4–13.5, P = 0.01) to race after injury compared to horses that were unraced at the time of injury. After injury horses had a small but significant reduction in racing performance. Main limitations: The series is a preselected population of Thoroughbred racehorses which referring veterinary surgeons considered potential candidates for surgical repair. Conclusion: Fracture configurations can be identified radiographically but is not a reliable predictor of comminution or other intra‐articular lesions. Arthroscopy not only directs repair but also identifies and facilitates management of concurrent lesions. The results reported should assist in formulating appropriate prognoses for Thoroughbred horses racing in the UK. [ABSTRACT FROM AUTHOR]

This study aimed to examine thirteen seasons of flat racing starts (n = 388,964) in the context of an ecological system and identify metrics that describe the inherent characteristics and constraints of the New Zealand Thoroughbred racing industry. During the thirteen years examined, there was a 2–3% per year reduction in the number of races, starts and number of horses. There was a significant shift in the racing population with a greater number of fillies (aged 2–4 years) having a race start, and subsequent longer racing careers due to the inclusion of one more racing preparation post 2008 (p < 0.05). Additionally, there was an increasingly ageing population of racehorses. These changes resulted in more race starts in a career, but possibly because of biological constraints, there was no change in the number of race starts per season, starts per preparation, or days spelling between preparations (p < 0.05). There was no change in the proportion of horses having just one race start (14% of new entrants), indicating that the screening for suitability for a racing career remained consistent. These data identify key industry parameters which provide a basis for future modelling of intervention strategies to improve economic performance and reduce horse injury. Consideration of the racing industry as a bio-economic or ecological model provides framework to test how the industry may respond to intervention strategies and signal where changes in system dynamics may alter existing risk factors for injury.

Summary: Background: A comprehensive study of the effect of supramaximal exercise in lipid homeostasis of Thoroughbreds provides the basis for future research on the role of lipids on energy metabolism in racehorses. Objective: To compare the plasma lipidome of Thoroughbreds before and after supramaximal exercise using an untargeted lipidomics approach. Study design: Pilot experimental study. Methods: Four Thoroughbred horses were used. The maximal oxygen consumption (VO2max) was calculated for each horse. Horses then underwent treadmill exercise at the speed for which the oxygen requirements had been calculated to be 115% VO2max. Plasma samples were obtained before (T0) and immediately (T1), 15 (T2) and 30 (T3) minutes post‐exercise, and evaluated using liquid chromatography/mass spectrometry. Data analysis consisted of principal component analysis and one‐way repeated measures analysis of variance. Results: A total of 933 plasma lipids were detected. Supramaximal exercise‐induced significant changes in the signal intensity of 13 lipids; all ubiquitous in the organism as major components of biological membranes or energy substrates. Main limitations: A treadmill was used to replicate track conditions. Also, sample size involved only four horses and the statistical analyses failed to achieve the desired power of 80%. Conclusions: The findings in this pilot study suggest that supramaximal exercise induces changes in specific plasma lipids in Thoroughbred racehorses. While the biological significance of these findings remains to be determined, these results provide baseline information for future studies in lipidomics applied to equine exercise physiology. Further research is warranted to better understand the role of lipids on energy metabolism in Thoroughbred racehorses. [ABSTRACT FROM AUTHOR]

Summary: Background: Race distance aptitude in Thoroughbred horses is highly heritable and is influenced largely by variation at the myostatin gene (MSTN). Objectives: In addition to MSTN, we hypothesised that other modifying loci contribute to best race distance. Study design: Using 3006 Thoroughbreds, including 835 'elite' horses, which were >3 years old, had race records and were sampled from Europe/Middle‐East, Australia/New Zealand, North America and South Africa, we performed genome‐wide association (GWA) tests and separately developed a genomic prediction algorithm to comprehensively catalogue additive genetic variation contributing to best race distance. Methods: 48,896 single‐nucleotide polymorphism (SNP) genotypes were generated from high‐density SNP genotyping arrays. Heritability estimates, tests of GWA and genomic prediction models were derived for the phenotypes: average race distance, best race distance for elite, nonelite and all winning horses. Results: Heritability estimates were high (hm2 = 0.51, best race distance – elite; hm2 = 0.42, best race distance – nonelite; hm2 = 0.40, best race distance – all) and most of the variation was attributed to the MSTN gene. MSTN locus SNPs were the most strongly associated with the trait and included BIEC2‐438999 (ECA18:66913090; P = 4.51 × 10−110, average race distance; P = 2.33 × 10−42, best race distance – elite). The genomic prediction algorithm enabled the inclusion of variation from all SNPs in a model that partitioned horses into short and long cohorts following assignment of MSTN genotype. Additional genes with minor contributions to best race distance were identified. Main limitations: The nongenetic influence of owner/trainer decisions on placement of horses in suitable races could not be controlled. Conclusions: MSTN is the single most important genetic contributor to best race distance in the Thoroughbred. Employment of genetic prediction models will lead to more accurate placing of horses in races that are best suited to their inherited genetic potential for distance aptitude. [ABSTRACT FROM AUTHOR]

Responses of equine skeletal muscle characteristics to growth and training have been shown to differ between breeds. These differential responses may arise in part because muscle fiber type and mitochondrial density differ between breeds, even in untrained racing-bred horses. However, it is not known when these breed-specific differences manifest. To test the hypothesis that weanling Standardbreds (SB) and Thoroughbreds (TB) would have higher mitochondrial measures than Quarter Horses (QH), gluteus medius samples were collected from SB (mean ± SD; 6.2 ± 1.0 mo; n = 10), TB (6.1 ± 0.5 mo; n = 12), and QH (7.4 ± 0.6 mo; n = 10). Citrate synthase (CS) and cytochrome c oxidase (CCO) activities were assessed as markers of mitochondrial density and function, respectively. Mitochondrial oxidative (P) and electron transport system (E) capacities were assessed by high-resolution respirometry (HRR). Data for CCO and HRR are expressed as integrated (per mg protein and per mg tissue wet weight, respectively) and intrinsic (per unit CS). Data were analyzed using PROC MIXED in SAS v 9.4 with breed as a fixed effect. Mitochondrial density (CS) was higher for SB and TB than QH (P ≤ 0.0007). Mitochondrial function (integrated and intrinsic CCO) was higher in TB and QH than SB (P ≤ 0.01). Integrated CCO was also higher in TB than QH (P < 0.0001). However, SB had higher integrated maximum P (PCI+II) and E (ECI+II) than QH (P ≤ 0.02) and greater integrated and intrinsic complex II-supported E (ECII) than both QH and TB (P ≤ 0.02), whereas TB exhibited higher integrated P with complex I substrates (PCI) than SB and QH (P ≤ 0.003) and higher integrated PCI+II and ECI+II than QH (P ≤ 0.02). In agreement, TB and QH had higher contribution of complex I (CI) to max E than SB (P ≤ 0.001), whereas SB had higher contribution of CII than QH and TB (P ≤ 0.002). Despite having higher mitochondrial density than QH and TB, SB showed lower CCO activity and differences in contribution of complexes to oxidative and electron transport system capacities. Breed differences in mitochondrial parameters are present early in life and should be considered when developing feeding, training, medication, and management practices. [ABSTRACT FROM AUTHOR]

Summary: Background: Upper respiratory tract (URT) endoscopic examination is a routine part of prepurchase examinations. Discrepancies have been documented in the assessment of arytenoid function grades (AFG) between veterinarians. Objectives: To document intra‐ and interobserver agreement for a population of multi‐experience level veterinarians for assessment of AFG of 2‐year‐old Thoroughbreds. Study design: Observational cohort study. Methods: One‐hundred and fourteen URT videoendoscopic examinations were evaluated by 10 veterinarians. Veterinarians were categorised based on experience, into five groups, each group with two veterinarians. Arytenoid function was graded using the Havemeyer ordinal scale and then reclassified by the authors dichotomously into 'meets conditions of sale' (MCS) or 'does not meet conditions of sale'(DNMCS). Interobserver agreement of arytenoid function was assessed across all 10 veterinarians using Fleiss' kappa and between veterinarians of similar experience levels in the five subgroups using Cohen's unweighted (k) and Cohen's linear weighted kappa (Ck). Intraobserver agreement was similarly calculated for each reviewer using 22 repeated video clips. Results: Overall interobserver agreement using ordinal scales was fair (k = 0.27, 95% CI 0.22–0.31) to moderate (mean weighted Ck = 0.57, 95% CI 0.46–0.69) depending on statistical methodology used. Using the dichotomous classification, interobserver agreement was good (k = 0.7, 95% CI 0.63–0.77). Overall intraobserver agreement using ordinal scales was fair (mean k = 0.26, 95% CI 0.14–0.38) to good (mean Ck = 0.61, 95% CI 0.50–0.71); and for the dichotomous reclassification it was good (k = 0.73, 95% CI 0.59–0.87). Experience level differences were identified. Main limitations: The low number of veterinarians in each experience subgroup. Conclusions: Subjectivity exists in arytenoid function grading, despite the existence of a well‐defined scale. Agreement variation exists depending on the grading scales and statistical methods used for analysis. Future studies pre‐ and post veterinarian training are indicated to determine if agreement can be improved. [ABSTRACT FROM AUTHOR]

The integrity of thoroughbreds is maintained under strict regulation involving DNA parentage testing, which is robust in a population with high genetic variability. The genetic variability of the thoroughbred population is possibly fluctuating because of selective breeding that has focused on adaptations for racing performance. To monitor genetic variability within the population and the effectiveness of short tandem repeat (STR) parentage testing, we investigated allele frequencies and the exclusion probability (PE) of 16–17 loci of a parentage panel in the Japanese thoroughbred population over 15 years. Expected heterozygosities (He) of 14 loci indicated a decreasing trend, and the average He of the population decreased significantly. Low genetic variability was possibly induced by a decrease in population size and a selective breeding bias. Four loci showed both a significant increase in allele frequency and a significant decrease in He; it is assumed that those loci were affected by positive selection for racing performance. There was a significant decrease in the PE because of the changes in genetic variability; however, it has remained over 0.99995. The current STR panel is still effective for parentage control, but it will be necessary to continuously monitor genetic variability, which has decreased over 15 years. [ABSTRACT FROM AUTHOR]

Summary: Background: Exercise‐induced pulmonary haemorrhage (EIPH) is considered a progressive disease based on histopathology, but it is unknown if tracheobronchoscopic EIPH severity worsens over time. Objectives: The aim of this study was to examine tracheobronchoscopic EIPH changes over time in a population of Thoroughbred racehorses. A secondary aim was to identify factors that affect changes in tracheobronchoscopic EIPH severity between observations. Study design: Prospective, longitudinal, observational cross‐sectional study. Methods: Thoroughbred racehorses were examined with tracheobronchoscopy no earlier than 30 min after racing. Examinations were recorded and graded blindly by experienced veterinarians using a 0–4 scale. Horses with 2 or more observations were included in the analysis. The association between the previous and current EIPH score was investigated using a linear mixed effect model. Factors associated with transitioning from a lower to a high EIPH grade and vice versa were examined using multiple ordinal regression. A semi‐parametric regression model was used to examine progression using the number of career starts as a marker for time. Models were adjusted for potential confounding variables. Results: There were 2974 tracheobronchoscopic examinations performed on 747 horses. Blood was detected in over half of all examinations (55.6%). The population prevalence of EIPH increased as the number of examinations for each horse increased. The preceding EIPH score was significantly associated with the current EIPH score. Significant variables associated with moving between EIPH grades were the number of days since last racing, ambient temperature and weight carried. Tracheobronchoscopic EIPH is mildly progressive over the first thirty career starts. Main limitations: Enrolment was voluntary. Horses were not followed for their entire career. Conclusion: Limiting the number of days in the current racing preparation and spacing races for horses with moderate to severe EIPH may be beneficial for reducing tracheobronchoscopic EIPH severity. The association between ambient temperature and EIPH warrants further investigation. [ABSTRACT FROM AUTHOR]

Summary: Background: The Province of Ontario maintains a registry of racehorse deaths occurring within 60 days of a race or trial entry that provides insight into mortality rates and costs of competition. Objectives: To characterise and quantify mortality and identify breed differences. Study design: Retrospective annualised cohort study. Methods: The Ontario Death Registry for 2003–2015, containing 1713 cases, was audited and information on the relationship between death and official work added. Race and trial data from industry performance databases were used to determine mortality rates according to breed, year, age, sex and circumstances of death. Results: Breed differences in mortality rate and individual risk were found. Thoroughbreds (Tb) had the greatest exercise‐associated mortality (EAM) rate and risk by all measures (2.27 deaths/1000 race starts, 0.95–1.0% annual individual risk), followed by Quarter horses (Qh, 1.49, 0.60–0.69%). Rate and risk were lowest for Standardbreds (Sb, 0.28, 0.23–0.24%). Nonexercise annual individual risk was highest for the Sb (0.45%, vs. Tb 0.33%, and Qh 0.32%). Pattern and type of EAM mirrored the characteristics of competitive activity in each industry, with high Tb and Qh mortality being associated with exercise and involving musculoskeletal injuries, dying suddenly and accidents. Low Sb EAM reflected the more extensive nature of training preparation and racing for this breed. Main limitations: Available data provided no information on morbidity, mortality beyond the 60‐day horizon or for horses not racing. Numbers for the Qh were low. Conclusions: Race‐intensity exercise is clearly hazardous for horses, with hazards varying widely between breeds and showing parallels with industry cultural and management norms. Breed differences provide insights concerning strategies that could reduce mortality, while improving welfare and reducing costs of participation. For all breeds, musculoskeletal injury was the major contributing cause of mortality. [ABSTRACT FROM AUTHOR]