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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.)

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.)

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]

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]

Summary: Background: Warmblood 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. Objectives: To 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 design: A single case report describing a genetic investigation. Methods: A 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. Results: Post‐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 limitations: This study is a single case report in the Thoroughbred with no additional cases from this breed yet identified to replicate this finding. Conclusions: Given 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. [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]

Background: Computed tomographic myelography can be a useful tool for evaluating vertebral canal stenosis. However, an index of spinal cord compression is yet to be established. Objectives: This observational descriptive study aimed to establish an index for spinal cord compression using computed tomography (CT). Methods: Twenty‐three Thoroughbred horses (age, 155–717 days; weight, 205–523 kg) with suspected cervical vertebral malformation were subjected to computed tomographic myelography in dorsal recumbency using large‐bore gantry CT to define the entire cervical vertebrae from C1 to C7. Subsequently, the height of the spinal cord was measured in the sagittal plane reformatted using curved multi‐planar reformation (MPR), thereby comparing it with stenotic ratio (i.e. dividing the area of spinal cord by that of the subarachnoid space) measured in the transverse plane. The measurement was performed at the level of each of six intervertebral spaces, for a total of 138 sites. Accordingly, the appropriate cut‐off value for spinal cord height was determined using the receiver‐operating characteristic curve, from which the area under the curve with 95% confidence interval was estimated. Results: The spinal cord compression cut‐off value was 7.06 mm, with an area under curve of 0.84. A weak relationship was observed between spinal cord height and stenotic ratio (R2 = 0.08, p < 0.05). Conclusions: Following curved MPR, a cut‐off value of 7.06 mm may serve as an index for spinal cord compression. [ABSTRACT FROM AUTHOR]

The number of horses leaving the Australian Thoroughbred (TB) racing industry each year is of concern to animal welfare advocates, public and regulators. A horse's previous athletic performance is a significant driver of retirement from racing. Racehorse performance can be measured in terms of the total number of starts, duration of racing and prize money earned. This study investigated Australian racing records for the 2005 and 2010 Victorian TB foal crops to identify factors associated with total number of starts, racing career duration, prize money earned and age of last race start‐up to the 10‐year‐old racing season. Racing Australia registered 4,577 TB horses born in Victoria in 2005 (n = 2,506) and 2010 (n = 2,071) that raced in Australia. Horses that started racing at 2‐years of age had fewer race starts in their first racing season but an increased total number of starts, prize money and duration of racing. The median age of last start (LS) was five (Q1 4; Q3 7) years. Horses that had won a race, had a maximum handicap rating of 61 or above and those racing over distances of more than 2,400 m had an increased racing career duration and an age of last race start greater than 6‐years of age. Horses participating in jumps races (n = 63) had the longest careers and older age of LS. These horses were more likely to have had a handicap rating over 80 and were just as likely to start their racing careers as 2‐years‐olds. [ABSTRACT FROM AUTHOR]

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]

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]

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]

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]

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]

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]

Background: Fragmentation of the dorsal aspect of the distal talus (FDDT), at the dorsolateral articular margin of the proximal intertarsal joint (PITJ) on pre‐sale radiographs of yearling Thoroughbreds has not been previously described and data to support decisions made by veterinarians to predict future racing potential of horses with these lesions are lacking. Methods: In this retrospective case–control study we aimed to determine the prevalence of FDDT in juvenile Thoroughbreds and to report their race records. From a database of survey and repository radiographic examinations of 5709 horses, 36 with FDDT were identified. Results: The prevalence of FDDT was 0.63% (36/5709; 95%CI 0.44, 0.87), compared with 5.01% (286/5709; 95%CI 4.46, 5.61) for osteochondrosis of the distal intermediate ridge of the tibia in the same population. In most cases, a single oval‐shaped fragment 1–12 mm in diameter was present. When comparing cases with matched controls, there were no significant differences in mean sale price, whether horses started in a trial or race and mean number of starts, wins, places and prize money when 2‐ and 3‐years old. Conclusion: FDDT did not appear to affect racing performance, although a larger‐scale study is warranted to confirm this finding. [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]

Summary: Background: There is a need for investigation of associations between intrasynovial medication and fracture risk in racehorses. Objectives: To document the proportion and type of fracture occurring following intrasynovial medication. Study design: Retrospective longitudinal study. Methods: Review of clinical records from all Thoroughbred flat racehorses receiving intrasynovial medication under the care of a first‐opinion veterinary practice between 2006 and 2011. Fractures pre‐ and post‐medication were categorised by location, type, and severity; analysis of fractures sustained within 56‐days of medication was undertaken. Survival analyses using Cox proportional hazards models were conducted for associations between medication used (corticosteroid vs. non‐corticosteroid), age at first medication, sex and total number of medications and fracture. Results: A total of 1488 horses received intrasynovial medication during the period of study; 8692 synovial spaces were medicated in 3925 sessions. There were 96 fractures that occurred within 56‐days of medication, of which 44 were classified as ‘serious’ (44/1488; 3.0% total population, 95% CI 2.1, 3.8%) and 11 (11/1488, 0.7%, 95% CI 0.3, 1.2%) were euthanased due to severity of injury. Fifty‐four of 96 cases (56.4%, 95% CI 46.3, 66.2%) returned to racing. Targeted imaging of the subsequent injury site was undertaken prior to injury in only 7 (7/96, 7.3%) horses that injured post‐medication. Horses that had received ≥3 previous intrasynovial medication sessions had an increased hazard of sustaining a fracture within 56 days (HR 2.31, 95% CI 1.51, 3.54, P<0.001) compared with those receiving ≤3 medication sessions, adjusted for each increasing year of age (HR 0.67, 95% CI 0.53, 0.86, P = 0.001). Main limitations: Absence of an unexposed cohort of nonmedicated racehorses. Conclusions: Serious musculoskeletal injury following intrasynovial medication occurred in 3% (44/1488) horses. Reduction in injury rates may be possible through greater use of premedication diagnostic imaging. [ABSTRACT FROM AUTHOR]

Summary: Background: Osteochondral fragmentation of the dorsoproximal margin of the proximal phalanx is commonly recognised in racing Thoroughbreds. Frequency distribution has been documented in racing Thoroughbreds and Quarter Horses in the USA and in European Warmbloods but no data have been published from the UK. Concurrent intra‐articular soft tissue lesions and radiographic accuracy of fragment distribution in racing Thoroughbreds have not previously been reported. Objectives: To document frequency distribution of dorsoproximal fragmentation of the proximal phalanx in a UK population of racing Thoroughbreds and to compare this with published data. To document concurrent intra‐articular lesions identified arthroscopically and radiographic accuracy of fragment distribution. Study design: A retrospective single centre‐based, observational study. Methods: Surgical reports and radiographs of all racing Thoroughbreds that underwent arthroscopic surgery for removal of fragmentation from the dorsoproximal margin of the proximal phalanx at Newmarket Equine Hospital between 2011 and 2015 were reviewed. Results: Two hundred and forty‐two (85.8%) horses were in or being prepared for flat racing. Osteochondral fragmentation of the dorsoproximal aspect of the proximal phalanx was present in 428 fetlock joints of 282 horses, consisting of 194 (45.3%) left and 188 (43.9%) right metacarpophalangeal joints, and 20 (4.7%) left and 26 (6.1%) right metatarsophalangeal joints. Fragmentation was located dorsomedially in 316 (73.8%), dorsolaterally in 32 (7.5%) and biaxially in 80 (18.7%) joints. Concurrent soft tissue lesions were identified in 168 (39.3%) joints. Radiographic evidence of fragmentation was visible in 320 joints (74.8%). Main limitations: Limited numbers preclude conclusions with respect to yearlings and horses in jump race training. Conclusion: Dorsoproximal fragmentation of the proximal phalanx occurred most frequently medially and in the forelimbs. Sidedness was not demonstrated. Although similar to previously reported data, variance in limb distribution is evident. Further research is required to determine whether concurrent intra‐articular soft tissue lesions are aetiopathogenic or an additional result of the pathological changes leading to fragmentation. Fragmentation site was not always accurately identified radiographically. The Summary is available in Spanish ‐ see Supporting information. [ABSTRACT FROM AUTHOR]

Summary: Background: Racing performance is often used as a measurable outcome variable in research studies investigating clinical diagnoses or interventions. However, the use of many different performance measures largely precludes conduct of meaningful comparative studies and, to date, those being used have not been collated. Objectives: To systematically review the veterinary scientific literature for the use of racing performance as a measurable outcome variable in clinical studies of racehorses, collate and identify those most popular, and identify their advantages and disadvantages. Study design: Systematic literature search. Methods: The search criteria “((racing AND performance) AND (horses OR equidae))” were adapted for both MEDLINE and CAB Abstracts databases. Data were collected in standardised recording forms for binary, categorical and quantitative measures, and the use of performance indices. Results: In total, 217 studies that described racing performance were identified, contributing 117 different performance measures. No one performance measure was used in all studies, despite 90.3% using more than one variable. Data regarding race starts and earnings were used most commonly, with 88.0% and 54.4% of studies including at least one measure of starts and earnings, respectively. Seventeen variables were used 10 times or more, with the top five comprising: ‘return to racing’, ‘number of starts’, ‘days to first start’, ‘earnings per period of time’ and ‘earnings per start’. Main limitations: The search strategies may not have identified all relevant papers, introducing bias to the review. Conclusions: Performance indices have been developed to improve assessment of interventions; however, they are not widely adopted in the scientific literature. Use of the two most commonly identified measures, whether the horse returned to racing and number of starts over a defined period of time, would best facilitate future systematic reviews and meta‐analyses in advance of the development of a gold‐standard measure of race performance outcome. [ABSTRACT FROM AUTHOR]

Background Incomplete ossification of the cuboidal bones of the carpus and tarsus in foals has the potential for significant consequences including chronic lameness and decreased athletic ability. Objectives To determine if the degree of ossification of the cuboidal bones is associated with gestational length and if the diagnosis of incomplete ossification is a predictor of performance in Thoroughbred racehorses. Study design Retrospective cohort study. Methods The medical records of Thoroughbred foals less than 90 days of age from 1994 to 2011 were examined and records containing tarsal radiographs identified. Radiographs of the tarsus were examined for signs of incomplete ossification and those that were incompletely ossified graded on a scale of 1-4 using a modification of a previously reported index, with Grade 1 being the least ossified and Grade 4 being the most. Gestational length was determined by examining breeding records and foaling dates reported to the Jockey Club. Race records for 2- and 3-year-old affected foals and their maternal siblings were obtained and compared. Results Foals with Grades 1 and 2 ossification were usually premature (gestation length <325 days), but Grades 3 and 4 were not. Foals with Grades 2 and 3 ossification were significantly less likely to race than their maternal siblings and Grades 1, 2, 3 and 4 foals earned less money. Main limitations A larger sample size of foals with Grade 1 ossification would increase the power of the study. Foals radiographed at an older age may have had lower ossification scores if radiographed earlier. Conclusions Incomplete ossification, especially Grades 1 and 2, is associated with a short gestation length. Foals with Grades 2 and 3 incomplete ossification were less likely to race and Grades 1, 2 and 3 earned around $30,000 less than their maternal siblings. [ABSTRACT FROM AUTHOR]

Background Few studies have described incidences of proximal limb and pelvic fracture ( PLPF) in Thoroughbred racehorses occurring on race day and during training. Information regarding clinical presentations and future racing careers in cases of PLPF is limited. Objectives To describe the incidence, clinical presentation and outcome of PLPF sustained by horses in racing and training at the Hong Kong Jockey Club ( HKJC) between 2003 and 2014. Study design Retrospective cohort study. Methods Horses with PLPF confirmed by nuclear scintigraphy, ultrasonography, radiography or post-mortem examination were identified using veterinary clinical records. Training and racing data for case horses were described. Incidences of fractures were estimated per 1000 horses in training and per 1000 race starts for fractures sustained during racing. Descriptive statistics were used to describe the study population. Results A total of 129 instances of PLPF were sustained by 108 racehorses. The most commonly fractured bone was the humerus (49.6%), followed by the tibia (29.4%). Nine horses sustained fatal fractures, eight of which occurred during racing. The incidence of fracture during racing was 0.30 per 1000 starts. Two-thirds of fractures occurred during training. The majority of horses presented with grade 3 lameness (n = 42 of 119 injury events, 35.3%). All horses presenting with grade 5 lameness sustained fatal injuries. Following noncatastrophic injury, all horses underwent box rest and 81 horses subsequently resumed racing; 45 of these won a race. Horses were retired at a median of 25 months (interquartile range: 15-36 months) after injury. Main limitations Protocols for resting non-training racehorses at the HKJC and for recording rehabilitation regimens post-injury prevented the calculation of horse days at risk. Conclusions The incidence of PLPF at the HKJC is low. Non-fatal PLPF is not necessarily a career-ending injury and many horses resume racing successfully following conservative treatment. [ABSTRACT FROM AUTHOR]

Background Exercise-induced pulmonary haemorrhage ( EIPH) is commonly implicated as a cause of poor athletic performance but there is limited and conflicting evidence for this association. Objectives The aim of this study was to determine if EIPH, based on endoscopic examination after racing, is associated with a variety of novel and established performance parameters. Study design Prospective, observational cross-sectional study. Methods Thoroughbred racehorses competing between 2012 and 2015 were examined on-course no earlier than 30 min after racing. Examinations were recorded and graded blindly by experienced veterinarians using a 0-4 scale. Linear mixed effect models were used for analysis of continuous response variables with horse name incorporated as a random effect to account for repeated sampling and horse variability. Generalised estimating equations were used for analysis of binary responses. Performance variables were examined in 2 models, comparing EIPH grade 0 to grades 1-4, and EIPH grade ≤2 compared with EIPH grades ≥3, controlling race factors that could influence performance. Results There were 3794 observations collected from 1567 horses. EIPH was detected in 55.1% of observations. Horses with grade 4 EIPH were significantly more likely to have a lower finishing position and finish further behind the winner, less likely to place in the first 3 positions and collect race earnings, collected less earnings per race start and were slower over the last 600 m of the race than horses without EIPH (grade 0). Similar associations were seen in Model 2, with horses with EIPH grade ≥3 having inferior performance when compared to horses with EIPH ≤2. Main limitations Enrolment was voluntary. Conclusion Mild to moderate haemorrhage was not associated with inferior race day performance in this population of Thoroughbred racehorses. [ABSTRACT FROM AUTHOR]

Background Osteochondrosis is considered multifactorial in origin, with factors such as nutrition, conformation, body size, trauma and genetics thought to contribute to its pathogenesis. Few studies have investigated the effects of genetic variability of osteochondrosis in Thoroughbreds. Objectives To describe the prevalence and genetic variability of a subset of osteochondrosis lesions in a group of Thoroughbred yearlings. Study design Retrospective cohort study. Methods Radiographs of 1962 Thoroughbred yearlings were retrieved from clinical records obtained between 2005 and 2013. Pedigree information was obtained from the Australian Stud Book. Osteochondrosis lesions were documented in selected joints and estimates of heritability were obtained by fitting linear mixed models in ASREML software. Results The overall prevalence of osteochondrosis was 23%. Osteochondrosis was identified in 10% of stifle joints, 6% of hock joints and 8% of fetlock joints. The heritability estimates ranged from 0 to 0.21. The largest estimates were 0.10, 0.14, 0.16 and 0.21 for lesions of the distal intermediate ridge of the tibia, dorso-proximal proximal phalanx (P1), any stifle osteochondrosis, and lesions of the lateral trochlear ridge of the distal femur, respectively. Although calculated heritability estimates had high standard errors, meta-analyses combining the present results with published estimates were significant at 0.10, 0.17, 0.15 and 0.20 for stifle, tarsal, fetlock and these joints combined, respectively. In addition, there was a permanent environment attributable to the dam effect. Main limitations Inclusion criteria were based on radiographic findings in specific joints at a specific age range in Thoroughbreds. Conclusions The present results indicate that only a proportion of osteochondrosis in Thoroughbreds is heritable. The permanent environment effects of the dam were observed to have effects on some categories of osteochondrosis. [ABSTRACT FROM AUTHOR]

Reasons for performing study Outcomes associated with arthrodesis of the proximal interphalangeal ( PIP) joint in Quarter Horses used for Western performance activities are well documented but little is known regarding outcomes for other types of horses. Objectives To identify factors associated with outcomes, including breed and activity, after arthrodesis of the PIP joint in Warmbloods, Thoroughbreds and Quarter Horses. Study design Retrospective case series. Methods Surgical case records of 82 Quarter Horses principally engaged in Western performance and Thoroughbred or Warmblood breeds principally engaged in showing, showjumping and dressage, with arthrodesis of the PIP joint were reviewed. Arthrodesis was performed with either 3 transarticular cortex bone screws placed in lag fashion, a dynamic compression plate ( DCP) with 2 transarticular cortex bone screws placed in lag fashion, or a locking compression plate ( LCP) with 2 transarticular cortex bone screws placed in lag fashion. Demographic data, clinical presentation, radiographic findings, surgical technique, post operative treatment and complications were recorded. Long-term follow-up was obtained for all 82 horses. Results Osteoarthritis of the PIP joint was the most common presenting condition requiring arthrodesis, which was performed with either the 3 screw technique (n = 41), DCP fixation (n = 22), or LCP fixation (n = 19). Post operatively, 23/31 (74%) Warmbloods/Thoroughbreds and 44/51 (87%) Quarter Horses achieved successful outcomes. Thirteen of 23 (57%) Warmbloods/Thoroughbreds and 24 of 38 (63%) Quarter Horses, used for athletic performance, returned to successful competition. Within this subgroup of horses engaged in high-level activity, regardless of breed type, horses undergoing hindlimb arthrodesis were significantly more likely to return to successful competition (73%; 33/45) than those with forelimb arthrodesis (25%; 4/16, P = 0.002). Conclusions Arthrodesis of the PIP joint in Warmbloods/Thoroughbreds and Quarter Horses results in a favourable outcome for return to their intended use and athletic competition. [ABSTRACT FROM AUTHOR]

Reasons for performing study Sesamoiditis is a common radiological finding in yearling Thoroughbreds. The condition is believed to be associated with suspensory ligament branch injury ( SLBI), which is known to affect racing performance. The presence of subclinical suspensory ligament branch change ( SSLBC) in untrained yearlings has not been investigated. Associations between sesamoiditis, SSLBC and subsequent SLBI would allow more accurate prognoses to be made regarding the development of SLBI. They could also provide opportunity for intervention and prevention of SLBI. Objectives To test our hypotheses that untrained yearling Thoroughbreds with sesamoiditis would be more likely to have ultrasonographic findings of SSLBC and those horses with concurrent sesamoiditis and SSLBC would be more likely to develop clinical suspensory ligament branch injury with training. Study design Prospective, cohort, observational study. Methods Yearling Thoroughbreds located at a single training centre were evaluated at the onset of their training careers and for the next 9 months. Radiographic and ultrasonographic examination of bilateral forelimb proximal sesamoid bones and suspensory ligament branches was performed. Results Fifty horses were eligible, resulting in 200 forelimb sesamoid/suspensory ligament branch pairs. A significant relationship existed between possibly significant ( PS) sesamoiditis and PS SSLBC (P<0.001). The odds ratio of sesamoids with PS sesamoiditis also demonstrating concurrent PS SSLBC was 5.1 (95% confidence interval 2.68-9.70, P<0.001). A significant relationship also existed between the concurrent presence of PS sesamoiditis and PS SSLBC and the subsequent development of clinical signs of SLBI (P<0.001, odds ratio 11.7, 95% confidence interval 4.1-33.4). Conclusions The associations identified in this study highlight the importance of ultrasonographic examination of suspensory ligament branches in horses with PS sesamoiditis. This information should allow more accurate prognostic advice regarding potential SLBI development and also provide opportunities for intervention and prevention of clinical SLBI. The Summary is available in Chinese - see Supporting information [ABSTRACT FROM AUTHOR]

Reasons for performing study Ambient temperature has been identified as a risk factor for exercise-induced pulmonary haemorrhage ( EIPH) in racing Thoroughbreds. This warranted a more expansive investigation of climatic conditions on the incidence and severity of EIPH. The impact of other variables such as the type of bit used, tongue ties and nonstandard shoes has not been reported and also warrant investigation. Objectives To examine the effect of various climatic variables as contributing risk factors for EIPH. Other previously uninvestigated variables as well as standard track and population factors will also be examined. Study design Cross-sectional study. Methods Thoroughbred racehorses competing at metropolitan racetracks in Perth, Western Australia were examined 30-200 min post race with tracheobronchoscopy. Examination took place at 48 race meetings over a 12 month period. Examinations were graded (0-4), independently by two experienced veterinarians. Univariable analyses were performed and variables with a P<0.25 were entered into a multivariable logistic regression analysis. The analysis was performed twice using the presence of blood ( EIPH grade 0 vs. grades ≥1) and EIPH grades ≤1 vs. EIPH grades ≥2 as dependent variables. Results Exercise-induced pulmonary haemorrhage was diagnosed in 56.6% of observations. Lower ambient temperature was significantly associated with EIPH grades ≥1 ( OR 0.95; 95% CI 0.93-0.98) and EIPH grades ≥2 ( OR 0.97; 95% CI 0.94-1.0). Bar shoes were significantly associated with EIPH grades ≥1 ( OR 6.35; 95% CI 2.17-18.54) and EIPH grades ≥2 ( OR 2.72; 95% CI 1.3-5.68). Increasing race distance was significantly associated with EIPH grade ≥1 and increasing lifetime starts was significantly associated with EIPH grade ≥2. Conclusions Ambient temperature is a risk factor for EIPH in Thoroughbred racehorses, with lower temperatures associated with increased risk. Bar shoes are a novel risk factor for EIPH in this population. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the prevalence of Malassezia species from the body skin and external ear canal of healthy horses. The samples were obtained by scraping the skin surface from the nose, groin and dorsum and swabbing from the external ear canal of 163 animals, and then incubated on sabouraud dextrose agar and modified Dixon agar. Malassezia species were isolated from 34.9% of horses. The percentages of Malassezia species were 64.3% for Arab, 35.7% for Persian, 35.4% for Thoroughbred and 27.1% for Turkmen breeds. The greatest abundance of Malassezia species was found in the external ear canal (47.7%, representing significant difference with other sites), followed by nose (26.3%), groin (15.8%) and dorsum (10.5%) ( P < 0.05). A total of 57 strains from six Malassezia species were detected with a frequency rate as follows: M. pachydermatis (33.3%), M. globosa (26.3%), M. sympodialis (14.1%), M. restricta (10.5%), M. obtusa (8.8%) and M. furfur (7%). The most common age-group affected was 1-3 years (59.4%). This study confirmed that cutaneous Malassezia microbiota in healthy horses varies by body site and age but not by breed and gender, representing M. pachydermatis as the most prevalent species on horse skin. [ABSTRACT FROM AUTHOR]

Abstract: The experiment was conducted to estimate dietary threonine (Thr) requirement using plasma amino acid concentrations as a criterion in mature thoroughbreds. Four adult thoroughbreds were used, and a 4 × 4 Latin square design was used for four dietary Thr levels. Plasma Thr concentration was constant until 0.41%, and then increased rapidly with increasing dietary Thr levels. The Thr requirement was estimated to be 67% of lysine with plasma Thr concentration at four Thr levels. [ABSTRACT FROM AUTHOR]

Background Decreased efficacy of antimicrobials and increased prevalence of multidrug resistance ( MDR) is of concern worldwide. Objectives To describe and analyze bacterial culture and antimicrobial susceptibilities from respiratory samples submitted from young horses (4 weeks to 3 years old). Animals Samples from 289 horses were submitted to a commercial laboratory. Methods A retrospective database search of submissions made to a New Zealand veterinary laboratory between April 2004 and July 2014. The results of in vitro susceptibility testing by Kirby-Bauer disc diffusion were described and tabulated for the major bacterial species isolated. Multiple correspondence analysis ( MCA) was used to describe the clustering of MDR isolates and selected demographic variables. Results Overall, 774 bacterial isolates were cultured from 237 horses, the majority of these isolates were gram-positive (67.6%; 95% CI 64.3-70.9%). Streptococcus spp. were the most common genus of bacteria isolated and were 40.1% (95% CI 36.6-43.5%) of the isolates cultured. Susceptibility of Streptococcus spp. to penicillin, gentamicin, and ceftiofur was >85%. Overall, gram-negative susceptibility to ceftiofur, tetracycline, and TMPS was <75%. MDR was defined as resistance to 3 or more antimicrobials, and was found in 39.2% of horses (93/237; 95% CI 33.0-45.5%). Conclusions and clinical importance Culture and susceptibility results have highlighted that MDR is an emerging problem for young horses in New Zealand (NZ), where a bacterial respiratory infection is suspected. This should be considered when prescribing antimicrobials, and emphasizes the need for submission of samples for culture and susceptibility. [ABSTRACT FROM AUTHOR]

Reasons for performing study Fracture of the metacarpal/tarsal condyle is usually preceded by prodromal pathology. Early recognition of injury is desirable to minimise the risk of serious breakdown; however, the clinical and diagnostic characteristics of unicortical condylar fractures have been poorly documented to date. Objectives To describe the clinical, imaging and outcome features of racehorses in first opinion practice diagnosed with short unicortical fracture of the metacarpal/tarsal condyle. Study design Retrospective case series. Methods All flat racehorses sustaining a unicortical condylar fracture while under the primary care of a single first opinion UK veterinary practice (2006-2013) were identified from imaging records and histories analysed for clinical presentation, lesion location, treatment, rehabilitation guidance and outcome. Results Forty-five cases were identified during the period of study. Forelimb injuries predominated (35/45, 77.8%). Mean age of cases was 3.4 ± 1.3 years. Palpable clinical abnormality referable to the fetlock region was not a feature. The majority (35/45, 77.8%) of injuries were diagnosed with radiography (flexed dorsopalmar/plantar projection), with the remainder requiring magnetic resonance imaging ( MRI) for diagnosis. Seven horses underwent surgery either at the time of original diagnosis or following reinjury. Twenty-eight of 30 horses (93.3%), not retired for unrelated reasons, returned to racing, with 5 (16.7%) conservatively managed horses sustaining reinjury at a median of 305 days. Misdiagnosis resulted in progression to catastrophic fracture in 2 cases. Conclusions Clinical findings associated with unicortical condylar fractures can be mild and appropriate diagnostic imaging is necessary for injury detection. Failure to detect injury can lead to catastrophic fracture. Most cases respond to conservative management and return to racing, but risk of reinjury merits consideration of surgery in selected cases. Veterinary vigilance and timely intervention has the potential to considerably reduce the incidence of complete condylar fracture of the fetlock in the racehorse. The Summary is available in Chinese - see Supporting information. [ABSTRACT FROM AUTHOR]

Reasons for performing study Peri-anaesthetic complications are relatively common in equine patients and further investigations are warranted to identify manageable risk factors. Objectives To report morbidity and mortality rates and identify associated risk factors for horses undergoing general anaesthesia, within a predominantly racing Thoroughbred ( TB) population. Study design Single centre retrospective observational study. Methods Anaesthetic and case records of all horses ≥12 months old undergoing general anaesthesia at Newmarket Equine Hospital between August 2010 and April 2012 were analysed, excluding emergency abdominal/dystocia procedures or traumatology cases with cardiovascular compromise. Mortality and morbidity rates were calculated and described. Uni- and multivariable analyses were used to investigate the relationship between the principal complication, post anaesthetic colic (PAC) and risk factors. Results A total of 1067 anaesthetic records of 1021 horses were included in the study; of these, 702 horses (65.8%) were TB, 169 (15.8%) developed a complication within 7 days of general anaesthesia and 10 (0.94%) died as a result. The most prevalent morbidity was PAC, 111 horses (10.5%) developed colic within 7 days of general anaesthesia. Thoroughbred horses (odds ratio [ OR] 2.93, 95% confidence interval [ CI] 1.73-4.96) and horses receiving sodium benzylpenicillin (Na BP) ( OR 2.77, 95% CI 1.69-4.50) were at increased risk of PAC. Conclusions Thoroughbred racehorses were identified as at increased risk of PAC in this study and might benefit from more critical evaluation of post anaesthetic gastrointestinal function. An alternative to the administration of Na BP for prophylactic antimicrobial therapy needs to be further investigated if its role in PAC is confirmed by other studies. [ABSTRACT FROM AUTHOR]

The objective of this study was to assess differences in serum protein expression profiles of Przewalski's ( Mongolian wild horse) and thoroughbred horses using proteome analysis. The serum proteins were separated by two-dimensional electrophoresis (2- DE) and five different gene products were identified. Proteins represented by the five spots were identified by matrix-assisted laser desorption ionization-time-of-flight ( MALDI- TOF) mass spectrometry ( MS)/ MS technology. The identities of all proteins were deduced based on their similarity to proteins in the human plasma protein database. Three proteins (a haptoglobin-2 alpha glycoprotein and two haptoglobin-2beta glycoproteins with different accession numbers) were downregulated in Przewalski's horse sera compared to thoroughbred horse sera. Moreover, two proteins (tetraspanin-18 and pM5) were upregulated in Przewalski's horses compared to thoroughbred horses. Haptoglobin-2 alpha and haptoglobin-2beta may serve as candidate molecules in future studies of inflammation, coagulation, immune modulation and pro-oxidant and antioxidant activity with consequential effects on the entire metabolism of the horse. [ABSTRACT FROM AUTHOR]

Reasons for performing study Recurrent laryngeal neuropathy ( RLN) causes airway obstruction and adversely affects racing performance in Thoroughbred racehorses. Prosthetic laryngoplasty ( PL) is the preferred treatment of RLN as it returns variables of airway mechanics to baseline. A number of materials have been evaluated as prostheses; however, the application of Lycra has not been rigorously investigated. Objective To evaluate the efficacy of PL using a Lycra prosthesis, in combination with transendoscopic, laser-assisted ventriculocordectomy, to restore racing performance in Thoroughbred racehorses with RLN. Study design Retrospective case series. Methods Medical records, preoperative and post operative racing performance indices from 78 Thoroughbred racehorses that underwent surgical treatment for RLN were evaluated. Medical records, preoperative and post operative racing performance indices were evaluated. Case history, post operative complications and PL failure were recorded. Racing performance was analysed using Beyer Speed Figures ( BSF), earnings and a performance index ( PI), with comparisons made between the 3 races before and after surgery. Factors associated with return to racing and racing performance were analysed. Results Eighty-two per cent (46/56) of horses that raced prior to surgery and 75% (15/20) of horses that had not raced prior to surgery competed in at least one race post operatively. Horses had a lower BSF and PI in the final race before surgery. Following surgery, PI and BSF values were restored to preoperative values in 73% and 78% of horses respectively. Surgical failure rate and immediate post operative complication rate were lower than, or comparable with, other reported prosthesis materials. Conclusions Thoroughbred racehorses with RLN have a good prognosis for racing successfully after PL using a Lycra prosthesis. The described surgical technique is associated with a low post operative complication rate and an increase in indicators of racing performance ( PI and BSF) post operatively. Lycra offers an attractive option for application as a prosthetic for PL with a low complication rate and similar efficacy to reported rigid prostheses. [ABSTRACT FROM AUTHOR]

Two variants in the equine myostatin gene ( MSTN), including a T/C SNP in the first intron and a 227-bp SINE insertion in the promoter, are associated with muscle fiber type proportions in the Quarter Horse ( QH) and with the prediction of race distance propensity in the Thoroughbred ( TB). Genotypes from these loci, along with 18 additional variants surrounding MSTN, were examined in 301 horses of 14 breeds to evaluate haplotype relationships and diversity. The C allele of intron 1 was found in 12 of 14 breeds at a frequency of 0.27; the SINE was observed in five breeds, but common in only the TB and QH (0.73 and 0.48 respectively). Haplotype data suggest the SINE insertion is contemporary to and arose upon a haplotype containing the intron 1 C allele. Gluteal muscle biopsies of TBs showed a significant association of the intron 1 C allele and SINE with a higher proportion of Type 2B and lower proportion of Type 1 fibers. However, in the Belgian horse, in which the SINE is not present, the intron 1 SNP was not associated with fiber type proportions, and evaluation of fiber type proportions across the Belgian, TB and QH breeds shows the significant effect of breed on fiber type proportions is negated when evaluating horses without the SINE variant. These data suggest the SINE, rather than the intron 1 SNP, is driving the observed muscle fiber type characteristics and is the variant targeted by selection for short-distance racing. [ABSTRACT FROM AUTHOR]