Thoroughbreds are a breed of horse known for their agility, speed, and spirit, often associated with horse racing and equestrian sports. Originating from crossbreeding native English mares with imported Arabian, Barb, and Turkoman stallions, Thoroughbreds have a well-documented pedigree that traces back to the late 17th and early 18th centuries. This breed is characterized by a refined head, deep chest, and long legs, contributing to their athletic capabilities. Thoroughbreds are primarily bred for their performance in racing but are also utilized in other equestrian disciplines. This page compiles peer-reviewed research studies and scholarly articles that explore the genetics, physiology, and performance characteristics of Thoroughbreds, as well as their management and welfare in various equine activities.
DITCHFIELD J, MACPHERSON LW.From outbreaks of upper respiratory infection of horses in the Toronto area between 1960 and 1963, several viruses have been isolated. The viruses, isolated in tissue cultures or eggs, include an equine strain of Myxovirus parainfluenzae 3; two strains of equine influenza virus, A/equi-1/Prague/56, and A/equi-2/Miami/63; equine rhinopneumonitis virus, and two newly recognized viruses of the horse, equine rhinoviruses. In addition serological evidence suggested a widespread infection with these viruses in the population under study. Because of the identical clinical picture seen and the complex...
Choi Y, Rosanowski SM, Parkin TD.To identify risk factors associated with complete humerus fractures in Thoroughbreds in South Korea. Unassigned: A retrospective case-control design with multivariable logistic regression was used. This study included 131 Thoroughbreds diagnosed with complete humerus fractures following racetrack activity between 2009 and 2022 (inclusive). Additionally, 660 healthy Thoroughbreds (699 observations) with at least 1 racetrack activity during the same period were included as controls. Unassigned: A total of 8 variables were associated with the risk of complete humerus fractures. Notably, horses wi...
Ursini TL, Clayton HM, Levine D, Richards J.To measure intersegmental movement in the sagittal, dorsal, and transverse planes of the cranial thoracic to caudal thoracic, caudal thoracic to lumbar, and lumbar to sacral segments using range of motion and angular velocity as measures of quality of movement. Unassigned: 6-degrees-of-freedom spinal motion was measured at the walk and trot in 3 sound Thoroughbred and Thoroughbred cross horses, and the data were pooled, giving a total of 54 gait cycles at walk and 33 at trot. These were compared against 8 cycles at walk and 13 at trot from 1 Thoroughbred horse that was confirmed as having mode...
Sullivan J, Blea J, McKemie DS, Kass PH, Knych HK.The pharmacokinetics and pharmacodynamics of betamethasone following intra-articular administration to horses have been described; however, studies characterizing intramuscular administration are lacking. Twenty-four horses received an intramuscular dose of 12 mg betamethasone sodium phosphate/betamethasone acetate. Blood and urine were collected at post administration for up to 408 h. Concentrations of betamethasone were determined using LC-MS/MS and pharmacokinetic parameters determined using a Population PK three-compartment model. The duration of pharmacodynamic effects was assessed by...
Bramall LM, Hinnigan GJ, Wattam AD, Owen KR.This case report describes the successful hemithyroidectomy of the largest equine solid follicular adenoma described in the veterinary literature to date. A 19-year-old thoroughbred mare was referred to Oakhill Veterinary Centre for the surgical removal of a large, left-sided thyroid gland measuring 26cm in diameter. Pre-operative considerations, the hemithyroidectomy surgical technique as well as the intra- and post-operative complications encountered, are discussed. Following surgery the horse had no long-term complications and continues to thrive four and a half years post-operatively.
Markowitz JS.Equibase (EQB) race charts provide the official record of North American Thoroughbred races and often document catastrophic injury, euthanasia, or equine-ambulance transport. Because chart documentation and regulatory classification differ, fatalities occurring > 72 hours after a race fall outside international regulatory definitions applied by the Equine Injury Database (EID) and may not appear in EID aggregates. EQB charts confirm horse identity, race participation, finishing status, and last recorded start. Horseracing Wrongs (HRW), an advocacy group, publishes horse-level fatality data tha...
Chan ZYS, Ho W, Slobodova A, Parkes RSV, Forbes B, Pfau T.To investigate associations between contralateral (left-right) hoof width asymmetry and vertical movement asymmetry in racing Thoroughbreds. We hypothesized that forehoof differences would be associated with poll and withers movement asymmetry and hind hoof differences with pelvis movement asymmetry. Unassigned: This observational cross-sectional study included 169 Thoroughbred racehorses recently retired from clockwise racing and assessed the day of scheduled farriery work. Contralateral hoof width differences were quantified and movement asymmetry during trot measured using inertial sensors ...
Imai S, Sato R, Fujiwara R, Terui S, Kimura A, Ichijo T, Kasashima Y, Miyazaki T.A 15-year-old Thoroughbred gelding was presented for examination due to chronic corneal opacity in the right eye, which had been noted for several years. An ophthalmic evaluation revealed dense, irregular corneal opacity; an absence of the direct pupillary light reflex; and a positive dazzle reflex. Fluorescein staining was negative and cytology of a corneal conjunctival swab identified nucleated squamous epithelial cells, but no inflammatory cells. Slit-lamp examination failed to visualize intraocular structure, and the lesion was deemed to be chronic and irreversible. An obstacle-avoidance t...
Massie S, Léguillette R, Jones JH, Guigand C, Sides RH, Jones KB, Warlick LM, Thueson EL, Troudt TA, Bayly WM.Maximal intensity exercise in equine athletes induces pulmonary capillary stress failure and exercise-induced pulmonary hemorrhage (EIPH) secondary to excessive transmural pressure (Ptm). Furosemide decreases EIPH severity and pulmonary arterial (PAP) and pulmonary wedge (PAW) pressures. Objective: Assess the effects of furosemide on Ptm and EIPH during supramaximal exercise. Methods: Six fit retired Thoroughbreds with consistent EIPH Grade ≥ 2. Methods: Horses performed a controlled crossover design protocol, completing standardized treadmill tests (120%V̇O2max) before and 4 h after int...
Hein M, Volkmann N, Probst J, Kemper N, Venner M.This retrospective report investigated whether starting racehorses' training and racing early is associated with a less successful and a shorter racing career. The data of 600 Thoroughbred racehorses from the German Racehorse Association's archiving programme were evaluated. The horses were classified into three groups regarding their different ages when starting training and racing: early training (16-24 months old)/early racing (two years old); early training/late racing (>two years old); and late training (25-30 months). Statistical models investigated effects on the horses' length of caree...
Avison A, Pyle WG, Sears W, Physick-Sheard PW.Sudden cardiac death is a leading cause of athletic death in both humans and horses, making racehorses a potentially valuable model for investigating sudden cardiac death. Cardiac restitution ratio (QT/TQ interval) is used to assess arrhythmia risk in humans, but investigations in athletes are scarce. The objective was to characterize QT interval and cardiac restitution ratio in Thoroughbred racehorses during maximal effort. Automated restitution analysis was performed using 2709 pairs of cardiac cycles from 30 Thoroughbred horses during races. Cardiac cycles were obtained during: pre-race; ac...
Minamijima Y, Kuroda T, Maeda Y, Narita S, Yamashita S, Yamada M.Medetomidine, an α₂-adrenergic agonist, is widely used as a sedative in horses. While its pharmacological effects are established, limited data exist on elimination of its metabolites, 3'-hydroxy medetomidine (HMD) and 3'-carboxy medetomidine (CMD), which are of regulatory interest. HMD is currently targeted in plasma and urine under International Screening Limits (ISLs) established by the International Federation of Horseracing Authorities (IFHA). In this study, seven Thoroughbreds received 6.3 μg/kg of medetomidine intravenously. Blood and urine were collected for 96 h and analyzed b...
Alexeenko V, Tavanaeimanesh H, Stein F, Gold J, Hughes L, McCue M, Marr C, Durward-Akhurst S, Jeevaratnam K.Cardiac arrhythmias are common in healthy athletic horses and may lead to poor athletic performance or exercise-associated sudden death. Early detection of high-risk horses is an important goal of cardiovascular diagnostics. We hypothesised that non-linear analysis of electrocardiogram disorderliness can be used to identify horses exhibiting intermittent ectopic atrial and ventricular heart rhythm abnormalities at exercise using brief, artifact-free recordings of normal sinus rhythm electrocardiograms collected at submaximal heart rates. In a convenience prospective cross-sectional study, ambu...
Hernández-Avilés C, Ramírez-Agámez L, Varner DD, Raudsepp T, Love CC.Cases of stallion subfertility due to acrosome dysfunction have been recognized since the 1990s. While some of these were observed in stallions with reduced sperm motility and morphology, a more severe form has been reported in stallions with normal-to-excellent sperm quality parameters, which is also uniquely observed in individuals of the Thoroughbred registry. These stallions carry a susceptibility genotype (A/A-A A in the gene FKBP6, exon 5) for Impaired Acrosomal Exocytosis (IAE). Current clinical observations from our group have identified a few highly subfertile stallions from other bre...
Volding DM, Flores-Ahlschwede P, Cramer MJ, Landrock KK, Sayre KC, Welsh TH, Bordin AI, Piccione J, Cohen ND.To determine the effects of transfusion of Rhodococcus equi hyperimmune plasma (REHIP) on serum electrolyte and protein concentrations in neonatal foals. Unassigned: A prospective observational study of 355 privately owned Thoroughbred foals from 13 farms in New York and cross-sectional study of REHIP samples. Blood was collected immediately before and after transfusion of either 1 or 2 L of REHIP to foals, and serum samples were separated and frozen until tested for concentrations of sodium (Na), potassium (K), chloride (Cl), total protein (TP), albumin, and globulins. Samples (n = 90) of REH...
Ishimaru M, Kume K, Murase H, Sato F, Matsui A, Ohmura H, Taya K.Thoroughbreds born early in the year are believed to have an advantage in racing. However, the development of endocrine functions in early-born foals in the cold winter climate is unclear. The present study was conducted to elucidate the effect of birth month on the development of endocrine function in Thoroughbred foals born from February to May in Hokkaido by comparing hypothalamic-pituitary axis, adrenal and thyroid functions from birth to 24 weeks of age. Eighty-seven Thoroughbred foals were used to compare the changes in circulating luteinizing hormone (LH), follicle-stimulating hormone (...
Bannai H, Kambayashi Y, Kume K, Takebe N, Endo Y, Kawanishi N, Nemoto M, Tsujimura K.The endemic situation of respiratory disease caused by equine herpesvirus type-1 (EHV-1) and type-4 (EHV-4) was investigated in a training facility for Thoroughbred yearlings in Japan. Vaccination typically starts in mid-September or early October-only after all yearlings have arrived-leaving those introduced earlier unprotected. To bridge this immunity gap, a revised vaccination program that started earlier was implemented. In 2021-2022 and 2022-2023, yearlings were allocated to three groups according to their introduction dates. Each group received a live EHV-1 vaccine (Equi N Tect ERP, Niss...
Maeda Y, Kanno C, Sugiyama M, Yamamoto R, Sato S, Ando R, Noda R, Kawaguchi H, Takahashi F.A 17-year-old Thoroughbred stallion died suddenly after grazing. Necropsy revealed massive hemorrhage in the pericardial sac, suggesting cardiac tamponade. Aortic perforation was observed at the aortic origin, and hemorrhage was observed in and around the epicardium. Superficial observation of the aortic lumen revealed a transverse tear of the aortic wall at the bases of the right semilunar valve and septal semilunar valve. Fibro-osseous changes with calcification were histopathologically observed at the site of the rupture. A nodular goiter was observed in the left thyroid gland. The horse di...
Myers TJ, Sampson SN, Glass KP, Russell LA.Central tarsal bone (CTB) fractures are challenging to diagnose, and cross-sectional imaging is required for definitive characterization and surgical planning. This retrospective case series aims to provide the first description of high-field (3-T) MRI characteristics of CTB fractures, concurrent pathology, and clinical presentation in 8 performance horses. Unassigned: 8 horses (9 limbs) diagnosed with a CTB fracture on high-field MRI at one tertiary referral hospital between 2013 and 2023 were identified via electronic medical records search. Unassigned: Quarter Horses (6 of 8) used for Weste...
Ceriotti S, Clark-Price S, Cole R, Kramer A, Sandey M, Mora M.This case describes a 15-year-old Thoroughbred mare with fistulous withers that progressed to vertebral osteomyelitis and spinal epidural abscess (SEA), a severe complication that has yet to be reported. Initially treated with antibiotics and anti-inflammatory medication, the mare developed acute hindlimb ataxia and spastic paresis, suggesting spinal cord compression at T3-L3. Diagnostic imaging revealed vertebral fractures and abscessation, but vertebral canal involvement could not be confirmed. Despite aggressive medical therapy, including antimicrobials, corticosteroids, and neuroprotective...
Bacon EK, Parnell D, Muscatello G, McElroy J, Velie BD.The ongoing discussion surrounding the well-being of retired racehorses underscores the importance of implementing effective rehoming strategies that prioritise animal welfare. A significant knowledge gap persists regarding whether a horse's success in racing can be used to reliably predict its performance in different equestrian sports upon retirement from racing. Objective: To examine the association between racehorse performance metrics and eventing metrics in off-the-track Thoroughbreds that compete in eventing within Australia. Methods: Racing metrics and eventing metrics for a sample of ...
Furukawa R, Tozaki T, Mizukami K, Iwasaki Y, Kawate K, Kikuchi M, Ishige T, Momozawa Y, Fukui E, Kakoi H.Thoroughbreds have been maintained as a closed breed for over 300 years since the crossbreeding between Arabian stallions and English mares. Despite interest in germline de novo mutations across species, their frequency in horses, particularly in Thoroughbreds, remains largely unexplored. Objective: This study aimed to identify de novo mutations in Thoroughbreds and estimate their frequency within a genetically closed population. Methods: We performed deep whole-genome sequencing (≥230× depth, 150 bp paired-end reads) and Sanger validation in a Thoroughbred trio (sire, dam, and foal). Reads...
Mc Sweeney D, Wang Y, Palmer SE, Holmströem M, Donohue KD, Farnsworth KD, Sanz MG, Lambert DH, Bayly WM.To determine whether screening of racing Thoroughbreds with accelerometer-based inertial measurement unit sensors and a specifically trained algorithm identified horses most at risk for fatal musculoskeletal injury (FMI) and whether age, gender, race distance, and track surface were associated with increased risk. Unassigned: Stride data from 28,481 races by 11,834 Thoroughbreds from July 25, 2021, until May 4, 2024, were assigned an algorithm-based risk score from 1 to 6 (6 = greatest risk). Logistic regression models examined the association between incidence of fatal injuries and risk score...
Mouncey R, de Mestre AM, Verheyen KL.Analyses of industry-level data suggest that around one-third of the UK and Ireland Thoroughbred foal crop fail to enter training. Prospective follow-up of individual horses could provide additional insight, particularly around individuals not attaining specific career milestones. Methods: A Thoroughbred birth cohort was established on stud farms across the UK and Ireland. Training, race performance, sales, export data, destinations and reasons for individuals failing to meet career milestones were collected from stud records, follow-up with owners, stud book and racing authorities' databases,...
Kim D, Lee S, Oyungerel B, Cho G.This study aimed to generate information for parentage testing in horse breeds using microsatellites (STRs) and single-nucleotide polymorphisms (SNPs). Genotype data were obtained from 189 horse hair root samples, including 38 Thoroughbreds (TBs), 17 Jeju horses (JHs), 20 Quarter horses (QHs), 21 American Miniatures (AMs), and 93 Mongolian horses (MHs), using 15 STR markers and 71 SNP markers. Comparative analysis revealed that the mean expected heterozygosity ranged from 0.468 (AM) to 0.491 (JH) for SNPs and from 0.695 (TB) to 0.791 (MH) for STRs. The mean observed heterozygosity ranged from ...
Pan M, Malekipour F, Pivonka P, Morrice-West AV, Flegg JA, Whitton RC, Hitchens PL.Fractures of the distal limb in Thoroughbred racehorses primarily occur because of accumulation of bone microdamage from high-intensity training. Mathematical models of subchondral bone adaptation of the third metacarpal lateral condyles are capable of approximating existing data for Thoroughbred racehorses in training or at rest. To improve upon previous models, we added a dynamic resorption rate and microdamage accumulation and repair processes. Our ordinary differential equation model simulates the coupled processes of bone adaptation and microdamage accumulation, and is calibrated to data ...
Minamijima Y, Kuroda T, Okano A, Wakuno A, Yuasa R, Ishikawa Y, Nomura M, Kinoshita K, Yamada M.We examined the pharmacokinetics of intravenous pridinol in six thoroughbred horses. Each horse received a single 20 mg dose of pridinol mesylate via the jugular vein, and plasma and urine samples were collected over 72 h. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to quantify pridinol concentrations in plasma and urine, allowing for the calculation of pharmacokinetic parameters. A three-compartment model best fit the plasma elimination data. Using the Toutain model, irrelevant plasma and urine concentrations were estimated to be 0.00284 and 0.000612 ng/mL, respec...
Maniego J, Swinburne J, Hincks P, Habershon-Butcher J, Given J, Ryder E.Gene editing and genome manipulation offer great promise for treating diseases in both humans and animals. There is a danger, however, that this technology could be used for other purposes such as performance enhancement. To detect such 'gene doping' events, we evaluated a targeted enrichment panel and next-generation sequencing to assess its reproducibility, sensitivity, and capability of variant detection on a wide variety of samples and biological matrices. The panel was verified against existing data for the myostatin gene, a PCR-based SNP panel, and whole genome sequencing in a subset of ...
Beck C, Hitchens PL, Muir P, Whitton RC.Computed tomography (CT) is increasingly used for metacarpo/tarsophalangeal or fetlock joint (MC/TPJ) evaluation in Thoroughbred racehorses. CT features and lesion prevalence in competing Thoroughbreds are unknown. Objective: To identify standing CT features within the MC/TPJ of elite Thoroughbred staying racehorses. Methods: Retrospective cohort study. Methods: Computed tomography scans of the MC/TPJ were performed as part of pre-race screening for fracture risk and graded for CT features. Descriptive statistics and univariable logistic regression models were generated to investigate associat...
Kuroda T, Knych HK, Noble GK, Minamijima Y, Leung GN, Nomura M, Mizobe F, Ishikawa Y, Kusano K, Toutain PL.Flunixin meglumine is widely used to manage pain and inflammation in horses, and its regulation requires robust pharmacokinetic analysis for harmonization. In this study, we conducted a meta-analysis of flunixin disposition using plasma and urine concentration data from 65 horses across four countries to robustly estimate pharmacokinetic parameters in setting screening limits (SLs) for controlling medications in horses. A population (POP) model was developed using nonlinear mixed-effects model analysis. The irrelevant plasma concentration (IPC) and irrelevant urine concentration (IUC) were det...
Hanousek K, O'Hara V, Riddell DO, Piercy RJ.In Thoroughbred horses, a highly prevalent short interspersed nuclear element (SINE) mutation in the myostatin gene (MSTN) promoter influences circulating myostatin concentration and is associated with muscle morphology, fracture risk and optimal race distance. Our prior data reveal that within horses there is substantial variation in serum myostatin concentration, particularly in MSTN heterozygotes and wild type horses but it was unclear whether such variation relates to within-horse differences or to environmental or temporal effects. Here we report the intra-horse consistency of circulating...
