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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.

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.)

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]

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: 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]

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: Racehorses may experience exercise-induced bronchodilation or bronchoconstriction, with potential differences between healthy and asthmatic individuals., Objectives: To identify exercise-related lung function variations by oscillometry in racehorses, compare lung function between healthy and mild equine asthma (MEA) horses, assess oscillometry's potential as a predictor of racing fitness., Study Design: Prospective case-control clinical study., Methods: Fourteen Thoroughbred racehorses (5 healthy, 9 MEA) underwent a protocol including respiratory oscillometry at rest, exercise with fitness monitoring, oscillometry at 15 and 45 min post-exercise, and bronchoalveolar lavage fluid (BALf) cytology. Oscillometry parameters (resistance [Rrs] and reactance [Xrs]) were compared within and between healthy and MEA groups at different timepoints. Associations between Rrs and Xrs at rest and 15 min post-exercise and BALf cytology and fitness indices were evaluated., Results: MEA horses showed higher Rrs at 15 min post-exercise (0.6 ± 0.2 cmH 2 O/L/s) than healthy horses (0.3 ± 0.1 cmH 2 O/L/s) (p < 0.01). In healthy horses, Rrs decreased at 15 min post-exercise compared with resting values (0.5 ± 0.1 cmH 2 O/L/s) (p = 0.04). In MEA horses, oscillometry parameters did not vary with time. Post-exercise Xrs inversely correlated with total haemosiderin score (p < 0.01, r 2  = 0.51). Resting Rrs inversely correlated with speed at 200 bpm (p = 0.03, r 2  = -0.61), and Xrs with maximum heart rate (HR) during exercise (p = 0.02, r 2  = -0.62). Post-exercise Rrs inversely correlated with mean (p = 0.04, r 2  = -0.60) and maximum speed (p = 0.04, r 2  = -0.60), and HR variability (p < 0.01, r 2  = -0.74)., Main Limitations: Small sample size, oscillometry repeatability not assessed, potential interference of upper airway obstructions, external variables influencing fitness indices., Conclusions: Oscillometry identified lung function differences between healthy and MEA horses at 15 min post-exercise. Only healthy horses exhibited exercise-induced bronchodilation. Oscillometry showed potential in predicting subclinical airway obstruction., (© 2024 EVJ Ltd.)

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]

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: 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]

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 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 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 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]

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]

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]

Reasons for performing the study Limited information exists regarding the prognosis for juvenile racehorses sustaining injury to the suspensory ligament branch insertion ( JISBI). Objectives To investigate the effect of JISBI on racing performance; and to assess whether the severity of JISBI is prognostically important. Study design Retrospective cohort study. Methods Records were reviewed for 896 juvenile Thoroughbreds in training, to identify horses with JISBI limited to one branch (cases). The ability of cases to start a race was compared to their cohorts. Race records of maternal siblings were compared to cases. Results The prevalence of JISBI for this population was 9.5%. Cohorts were 3.2 times more likely to start as a 2-year-old and 3.6 times more likely to start as a 3-year-old compared to horses with JISBI. Of 58 cases that were compared to maternal siblings, the total earnings per start ( EPS), 2- and 3-year-old EPS were all reduced (P<0.01). Cases raced a mean of 3.8 times compared to 7.4 races for controls over the study period and were 113.2 days older by the time of first start (P<0.01). 'Speed figures' and EPS were, however, similar between cases that had raced and controls. Cases with a moderate-severe lesion (≥ Grade 2) were at significantly greater risk of reinjury than mild cases (P<0.05). Conclusions JISBI causes decreased racing ability as a 2-year-old. Mild cases perform similarly to controls by their 3-year-old season, but more severe cases demonstrate reduced ability as a 3-year-old, with an increased likelihood of reinjury. Although the wastage was higher in case horses with JISBI, individual cases that make it to a race have similar earnings per start as their controls. [ABSTRACT FROM AUTHOR]

Reasons for performing study Although fractures of the proximal phalanx are one of the most common long bone fractures of Thoroughbred horses in training, limited details on variations in morphology and radiological progression have been published. Objectives To describe in detail the configuration of parasagittal fractures of the proximal phalanx in a group of Thoroughbred racehorses, to report fracture distribution within this group of horses and to document radiological progression of fracture healing in cases treated by internal fixation. Study design Restrospective case series. Methods Case records and radiographs of Thoroughbred racehorses with parasagittal fractures of the proximal phalanx admitted to Newmarket Equine Hospital between 2007 and 2011 were analysed. Results One hundred and twenty-one fractures were identified in 120 Thoroughbred racehorses. Fractures were frequently more complex than was appreciated immediately following injury; a feature that has not been reported previously. There was seasonality of fractures in 2- and 3-year-old horses, but not in older horses. Conclusions and potential relevance Fractures of the proximal phalanx may be more complex than recognised previously, although often their complexity cannot be identified radiographically immediately following injury. The seasonality observed in 2- and 3-year-old horses is most likely to be a consequence of the timing of the turf-racing season in the UK. The Summary is available in Chinese - see Supporting information. [ABSTRACT FROM AUTHOR]

Reasons for performing study Fractures of the proximal phalanx are generally considered to result from monotonic supraphysiological loads, but radiological observations from clinical cases suggest there may be a stress-related aetiology. Objectives To determine whether there are radiologically identifiable prodromal changes in Thoroughbred racehorses with confirmed parasagittal fractures of the proximal phalanx. Study design Retrospective cross-sectional study. Methods Case records and radiographs of Thoroughbred racehorses with parasagittal fractures of the proximal phalanx were analysed. Thickness of the subchondral bone plate was measured in fractured and contralateral limbs, and additional radiological features consistent with prodromal fracture pathology documented. Results The subchondral bone plate was significantly thicker in affected than in contralateral limbs. Evidence of additional prodromal fracture pathology was observed in 15/110 (14%) limbs with parasagittal fractures, and in 4% of contralateral limbs. Conclusions The results of this study are not consistent with monotonic loading as a cause of fracture in at least a proportion of cases, but suggest a stress-related aetiology. Increased thickness of the subchondral bone plate may reflect (failed) adaptive changes that precede fracture. Potential relevance Better understanding of the aetiology of fractures of the proximal phalanx may help develop strategies to reduce the risk of fracture. The Summary is available in Chinese - see Supporting information. [ABSTRACT FROM AUTHOR]

Reason for performing study The use of triamcinolone acetonide ( TA) in performance horses necessitates establishing appropriate withdrawal times prior to performance. Objectives To describe the plasma pharmacokinetics of TA and time-related urine and synovial fluid concentrations following i.m. and intra-articular administration to exercised Thoroughbred horses. Study design Block design. Methods Twelve racing fit adult Thoroughbred horses received a single i.m. administration of TA (0.1 mg/kg bwt). After an appropriate washout period, the same horses then received a single intra-articular TA administration (9 mg) into the right antebrachiocarpal joint. Blood, urine and synovial fluid samples were collected prior to, and at various times, up to 60 days post drug administration and analysed using liquid chromatography-mass spectrometry. Plasma data were analysed using noncompartmental analysis. Results Maximum measured plasma TA concentrations were 0.996 ± 0.391 at 13.2 h and 1.27 ± 0.278 ng/ml at 6.5 h for i.m. and intra-articular administration, respectively. The plasma terminal elimination half-life was 11.4 ± 6.53 and 0.78 ± 1.00 days for i.m. and intra-articular administration, respectively. Following i.m. administration, TA was below the limit of detection ( LOD) by Days 52 and 60 in plasma and urine, respectively. Following intra-articular administration TA was undetectable by Day 7 in plasma and Day 8 in urine. Triamcinolone acetonide was also undetectable in any of the joints sampled following i.m. administration and remained above the limit of quantitation ( LOQ) for 21 days following intra-articular administration. Conclusions and potential relevance This study extends previous studies describing the pharmacokinetics of TA following i.m. and intra-articular administration to the horse and suggests that plasma and urine concentrations are not a good indicator of synovial fluid concentrations. Furthermore, results of this study supports an extended withdrawal time for TA given i.m. The Summary is available in Chinese - see Supporting information. [ABSTRACT FROM AUTHOR]

Reasons for performing study: Ultrasonographic (US) abnormalities of the suspensory ligament branch (SLB) have been poorly investigated but can have considerable impact on market value and career path when encountered in athletic horses. There is a need for determination of the prevalence and relationship to clinical injury of these US abnormalities in the Thoroughbred (TB) racehorse. Objectives: To establish the prevalence of, and the repeatability of an US grading system for, subclinical US abnormalities of the forelimb SLB in a population of UK TB flat racehorses. Methods: Ultrasonographic assessment of the forelimb SLBs of 60 TB racehorses free from history and clinical indication of SLB desmopathy in a single UK training yard was performed. Images were viewed independently by 2 blinded observers and graded for US abnormality. Interobserver agreement was assessed using Cohen's kappa statistic with 95% confidence intervals (95% CI). Results: Prevalence of horses with subclinical US abnormality of the forelimb SLB of moderate severity was 6.7%. Medial branches were overrepresented. Inter observer agreement was substantial for US grade (kappa = 0.743; 95% CI 0.652-0.834) and almost perfect for appearance of sesamoid bone at ligament insertion (kappa = 0.817; 95% CI 0.66-0.98). Conclusions: The study reveals that a proportion of TB racehorses in flat training free from history or clinical signs of SLB injury have US abnormalities that could negatively impact on market value and career path. Potential relevance: Clinicians should be aware that US abnormalities of the SLB may not always be related to clinical desmopathy. Further longitudinal studies are required to determine whether such findings are predictive for future injury. [ABSTRACT FROM AUTHOR]

Reasons for performing study: There is increasing evidence that exercise early in life has a positive effect on musculoskeletal health. At present, there is little whole population research investigating the effect of racing as 2-year-olds on future racing career. Objectives: To investigate the association between attaining training milestones as 2-year-olds with length of career and racing success in Thoroughbred horses in New Zealand. Methods: Retrospective data were obtained of the 2001/02-born Thoroughbred foal crop. The 3 training milestones were: registered with a trainer, trialled and raced. The association of the training milestones with career length was measured using the outcomes: number of race starts and number of years raced, in a Cox regression model. Logistic regression models analysed the association of the training milestones with the outcomes: won or placed in a race. Linear regression was performed to assess the association of training milestones with total career earnings. Results: Of 4683 horses in the population; 3152 horses were registered with a trainer, 2661 horses trialled and 2109 horses raced. Horses that raced as 2-year-olds had significantly (P<0.001) more race starts than those first raced as 3-year-olds or older, this was also true when the 2-year-old year data were omitted. Horses that raced as 2-year-olds had significantly (P<0.001) more years racing. Horses registered with a trainer, trialled or raced as 2-year-olds were more likely to have won or been placed in a race than those that achieved the milestones as 3-year-olds or older. Horses that first trialled and raced as 2-year-olds had greater total earnings than those that first trialled or raced at a later age. Conclusions and potential relevance: Two-year-old training milestones had a strong association with positive racing career outcomes. Horses in training or racing as 2-year-olds may have better musculoskeletal health throughout life than horses that are first in training or racing at a later age. [ABSTRACT FROM AUTHOR]

Reasons for performing study: Although fractures of the metacarpal and metatarsal condyles are the most common long-bone fractures of Thoroughbred horses in training, limited data on variations in morphology and incidence have been published. Additionally, grouped analyses of previous studies from the UK and USA would permit comparison between study groups and the creation of a substantial pool of international data. Methods: Retrospective analysis of case records of horses with fractures of the distal condyles of third metacarpal/metatarsal bones seen over the last 10 years at Newmarket Equine Hospital. The current series was compared with a prior series from the UK; pooled analyses of these, and series from the USA were also compared. Results: One hundred and seventy-four fractures were identified in 167 racehorses. The current series contained a significantly lower proportion of medial condylar fractures than in a similar population 17 years earlier. Fractures that originated more abaxially tended to be shorter, and a significant proportion of lateral condylar fractures arose outside of the condylar groove. There was also some apparent seasonality of fractures of the lateral condyles in 2-year-old horses, but not so in older horses or those with medial condylar fractures. Conclusions and potential relevance: A substantial portion (approximately 50%) of fractures in the present series cannot be explained by unifying theories of aetiopathogenesis, which suggest that fractures usually arise within the condylar groove, as a focus of cumulative fatigue and failure of adaptation of bone. A separate aetiopathogenesis may be responsible for a proportion of condylar fractures encountered in racehorses, and further work is required to elucidate this. Changes in the number of medial condylar fractures encountered may reflect the introduction of artificial racing and training surfaces, and also may reflect changes in the age demographic of horses racing in the UK since the introduction of year-round 'all-weather' racing. [ABSTRACT FROM AUTHOR]

Reasons for performing study: Improved education of veterinarians and equine owners/managers is essential in implementing parasite control strategies that are less reliant on chemicals. Methods: This questionnaire study, conducted on 61 UK Thoroughbred (TB) establishments during 2009 and 2010, was designed to obtain an understanding of current helminth control practices on studs. To our knowledge, this is the first occasion that statements obtained from TB studs via questionnaire have been supported by statistical analysis. Results: Despite many respondents indicating high levels of concern regarding anthelmintic resistance, 56% of these establishments that received visiting equines co-grazed these animals with permanent stock and <74% administered anthelmintics prior to integration. In the 12 months preceding the study, most respondents administered frequent macrocyclic lactone (ML) treatments, with none appearing to leave any animals in groups untreated at each administration. Indiscriminate whole group treatments with MLs and movement of animals to 'clean grazing' post treatment (reported by >25% of respondents), indicates that many stud owners/managers are not aware of the strong risk factors for the development of anthelmintic resistance. Few studs had conducted faecal egg count (FEC) analysis in the past and only 22% indicated that they considered this form of analysis beneficial in determining anthelmintic choice. Conclusions and potential relevance: The challenge now is to convince stud owners/managers to deviate from their current practices to control strategies that are more likely to preserve anthelmintic efficacy. Veterinarians need to get more involved in implementing these control strategies, with better emphasis placed on the role of diagnostic tests in facilitating targeted treatments and in investigating anthelmintic sensitivity in the associated nematode populations. [ABSTRACT FROM AUTHOR]

Reasons for performing study: Sudden death adversely affects racehorse welfare, jockey safety and the public perception of horseracing. Objective: To describe the risk of racing-associated sudden death in Thoroughbred racehorses in the UK from 2000 to 2007, to identify whether there were risk factors uniquely associated with sudden death and to improve the understanding of the pathogenesis of racing-associated sudden death by identification of risk factors for such cases. Methods: A sudden death was defined as an acute collapse and death, in an apparently healthy Thoroughbred racehorse, during or immediately after racing, in the absence of clinical data indicative of a catastrophic orthopaedic injury. The retrospective study included 201 case race starts and 705,712 control race starts. Univariable and multivariable logistic regression were used to identify risk factors for sudden death at any one start. Results: In the multivariable model, age, distance, race type, season and number of starts in the 60 days prior to the race were associated with sudden death. Conclusions: The risk factors identified in this study are not uniquely associated with sudden death and have been also been identified in studies using all causes of fatality as the outcome. These data suggest that a generic approach to reduce fatal musculoskeletal injury and sudden death may be possible. Potential relevance: The identification of risk factors allows speculation on the underlying mechanisms of sudden death in racing. This may stimulate hypothesis-led investigations into the pathogenesis of exercise-related arrhythmias, exercise-induced pulmonary haemorrhage and blood vessel rupture. [ABSTRACT FROM AUTHOR]

Sagittal fracture of the proximal phalanx (P1) is an important musculoskeletal injury of the performance horse. Although widely considered to be monotonic in nature, there is emerging evidence that some P1 fractures may have stress-injury aetiology. Three cases are described in which imaging features found were suggestive of prodromal bone injury. All cases returned to full performance use after a period of rest. The authors conclude that it is possible that some P1 fractures in the Thoroughbred racehorse may develop through stress/fatigue injury pathways. It is proposed that intervention prior to overt fracture may be possible in some cases. [ABSTRACT FROM AUTHOR]