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

Objective This study was intended to identify genes positively selected in Thoroughbred horses (THBs) that potentially contribute to their running performances. Methods The genomes of THB and Jeju horses (JH, Korean native horse) were compared to identify genes positively selected in THB. We performed cross-population extended haplotype homozygosity (XP-EHH) and cross-population composite likelihood ratio test (XP-CLR) statistical methods for our analysis using whole genome resequencing data of 14 THB and 6 JH. Results We identified 98 (XP-EHH) and 200 (XP-CLR) genes that are under positive selection in THB. Gene enrichment analysis identified 72 gene ontology biological process (GO BP) terms. The genes and GO BP terms explained some of THB’s characteristics such as immunity, energy metabolism and eye size and function related to running performances. GO BP terms that play key roles in several cell signaling mechanisms, which affected ocular size and visual functions were identified. GO BP term Eye photoreceptor cell differentiation is among the terms annotated presumed to affect eye size. Conclusion Our analysis revealed some positively selected candidate genes in THB related to their racing performances. The genes detected are related to the immunity, ocular size and function, and energy metabolism.

PICO question In young Thoroughbreds with osteochondral fragments of the proximo-plantar aspect of the proximal phalanx, does pre-emptive surgical removal of the fragments compared to conservative (non-surgical) management reduce the incidence of subsequent lameness? Clinical bottom line There is currently insufficient data to determine the impact, on subsequent lameness, of conservative versus surgical management of proximo-plantar osteochondral fragments in young Thoroughbreds. Indeed, only three relevant studies were found, which include one retrospective study and two smaller case series. Since there are no substantive studies that have specifically focused on the treatment of plantar osteochondral fragmentation in Thoroughbred racehorses, the strength of evidence currently available is low.

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

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

For the past few decades a concern with heritage in the countries of the Arab Gulf has led to the reclamation of the purebred Arabian horse as one of the iconic animals of the Bedouin identity and to developing a thriving horse breeding industry in the region. While stud farms and equestrian sport events are intended to reinforce the Arabian identity of the breed, a closer look at its history demonstrate in fact the complexity of its identity. The complexity of cultural transfers with respect to horse breeding between the East and the West from the Early Modern period on, highlights the connected history of both the Arabian horses and the Thoroughbreds, and the ongoing cultural re-appropriation of both breeds as 'native' to the Arabian Peninsula. [ABSTRACT FROM AUTHOR]

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

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

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

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

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

Horses are one of the early domesticated animals in the world that changed societies and civilizations on a continent-wide scale. Due to the rare information about the genetic characterization of different horse populations in Egypt, this study aimed to identify the genetic biodiversity and relationships between four horse populations reared in Egypt. Genomic DNA was extracted and mtDNA region was amplified using polymerase chain reaction (PCR). The alignment of 384-bp amplified fragments showed the presence of 41 polymorphic sites resulting in 29 haplotypes which their sequences were submitted to GenBank under the accession numbers: KX909898-KX909926. The phylogeny tree for tested horses declared the presence of mixing maternal lineages between the four tested populations but still there are some separated lineages especially for Arabian and Thoroughbred horses. The sequences of 72 tested sequences were aligned with 13 published sequences as references, 11 of them for different Equus caballus whereas the other two reference sequences for Equus burchellii and Equus asinus. The results showed that all tested horses from the four populations are grouped with reference sequences of Equus caballus and separated from the other two reference sequences of Equus burchellii and Equus asinus. It is concluded that sequence analysis of mtDNA control region is still the most informative tool for the identification of genetic biodiversity and phylogeny of different horse breeds and populations. The horse populations reared in Egypt possess low genetic diversity and all of them are belonged to Equus caballus breed.

Objective Evaluation of exercise effects in racehorses is important in horseracing industry and animal health care. In this study, we compared metabolic patterns between before and after exercise to screen metabolic biomarkers for exercise effects in thoroughbreds. Methods The concentration of metabolites in muscle, plasma, and urine was measured by 1H nuclear magnetic resonance (NMR) spectroscopy analysis and the relative metabolite levels in the three samples were compared between before and after exercise. Subsequently, multivariate data analysis based on the metabolic profiles was performed using orthogonal partial least square discriminant analysis (OPLS-DA) and variable important plots and t-test was used for basic statistical analysis. Results From 1H NMR spectroscopy analysis, 35, 25, and 34 metabolites were detected in the muscle, plasma, and urine. Aspartate, betaine, choline, cysteine, ethanol, and threonine were increased over 2-fold in the muscle; propionate and trimethylamine were increased over 2-fold in the plasma; and alanine, glycerol, inosine, lactate, and pyruvate were increased over 2-fold whereas acetoacetate, arginine, citrulline, creatine, glutamine, glutarate, hippurate, lysine, methionine, phenylacetylglycine, taurine, trigonelline, trimethylamine, and trimethylamine N-oxide were decreased below 0.5-fold in the urine. The OPLS-DA showed clear separation of the metabolic patterns before and after exercise in the muscle, plasma, and urine. Statistical analysis showed that after exercise, acetoacetate, arginine, glutamine, hippurate, phenylacetylglycine trimethylamine, trimethylamine N-oxide, and trigonelline were significantly decreased and alanine, glycerol, inosine, lactate, and pyruvate were significantly increased in the urine (p

The reproductive parameters of 51 Thoroughbred mares were studied during the period 1997-2010. A total number of 270 oestrus and reproductive cycles were included in the analysis. Thoroughbred horses are only allowed to mate naturally by traditional hand method. As a source of information was used the zootechnical documentation of the national stud farm. It was established that the reproductive traits subject to the recent study varied in wide ranges - interval of foal heat (11.18±2.40-31.00±19.92 days) and foaling-to-conception (13.00±3.00-57.00±29.69 days), number of oestrus cycles (1.16±0.38-1.87±1.28), mating of mares (2.80±0.83-3.89±2.40) and total born foals (2-20) per year, duration of oestrus (21.00±2.51-26.00±7.07 days) and heat (3.00±2.22-5.09±1.95 days). The positive correlations were found between duration of oestrus cycle with number of matings per year and duration of heat, duration of heat and number of matings per year, foaling-to-conception interval with number of foals and foaling-to-conception interval and number of oestrus cycles per year. [ABSTRACT FROM AUTHOR]

Performance horses can require a tremendous amount of time, training, and finances to maintain optimal health and reach maximum fitness levels. Racehorses are one of the many performance horses that require such vigorous maintenance schedules to compete. Measuring heart rate variability (HRV) in these equine athletes can allow for post-training, postcompetition recovery and stress analysis. In this study, we measured HRV parameters in 13 Thoroughbred (TB) racehorses at Delta Downs Racetrack, located in Vinton, Louisiana. Data were recorded in short-term readings of 5 minutes at 0 to 1 hour post-race (depending on if they went to test-barn), 12 hours, and 24 hours post-race, in 7 TB racehorses. An additional 6 TB racehorses were recorded only at rest (no race or strenuous workouts for over a week). The R-R readings were less (P < 0.0001) at 0 to 1 hour post-race (753.6 ± 43.2) compared with 12 hours (1382.8 ± 44.5), 24 hours (1503.7 ±40.0) and rest (1370.9 ± 39.3). The heart rate (HR) was greater (P < 0.0001) at 0 to 1 hour post-race (82.8 ± 4.6) compared with 12 hours (43.9 ± 1.4), 24 hours (40.3 ± 1.4) and rest (44.0 ± 1.4). The RMSSD was less (P < 0.0001) at 0 to 1 hour post-race (16.9 ± 2.8) compared with 12 hours (31.6 ± 3.1), 24 hours (33.6 ± 1.6) and rest (33.6 ± 3.4). The SDNN was less (P < 0.0003) at 0 to 1 hours post-race (23.7 ± 2.9) compared with 12 hours (38.7 ± 2.9), 24 hours (36.8 ± 1.6) and rest (36.2 ± 2.7). The pNN50 was less (P < 0.0044) at 0 to 1 hour post-race (3.5 ± 3.2) compared with 12 hours (8.9 ± 1.8), 24 hours (11.8 ± 1.3) and rest (11.7 ± 2.9). None of the 12- and 24-hour readings were different from each other or at rest indicating these horses appeared to have recovered from their race within 12 hours. [ABSTRACT FROM AUTHOR]

• Risk factors for limb deformities (LD)were evaluated in a Thoroughbred birth cohort. • Twenty-one percent of foals required veterinary intervention for LD in the first 6 months of life. • Early-life LD were not observed in foals with gestation lengths >360 days. • Risk of early-life LD reduced by 4% per day increase in gestation length (GL). • At GL of 320 to 360 days the final model predicted a LD prevalence of 40% to 10%. Flexural and angular limb deformities (LD) are an important cause of early-life morbidity and mortality/euthanasia in Thoroughbred foals. The majority are congenital in origin but, to date, their precise aetiology is poorly understood. We hypothesized that maternal- and pregnancy-level factors, particularly those with potential to influence in-utero growth and development, could play an important role. The aim of this study was therefore to investigate associations between such factors and early-life LD in Thoroughbred foals. A birth cohort was established on seven farms across the United Kingdom and Ireland and details of veterinary interventions for LD in foals in the first six months of life prospectively recorded. Details of dams' signalment, breeding history and reproductive and veterinary history in the breeding season(s) of interest were retrieved retrospectively from stud farm and veterinary records. Associations between mare- and pregnancy-level factors and LD in offspring were assessed using multivariable logistic regression. Records were available for 275 pregnancies in 235 mares, over two breeding seasons. Pregnancies resulted in the birth of 272 live foals, 21% of which (n = 57/272, 95% CI, 16–26) required veterinary intervention for LD in the first six months of life. Odds of LD decreased by 4% per day increase in gestation length between 314 and 381 days (OR 0.96, 95% CI, 0.93–0.99, P =.01). Longer gestation length appears to reduce the odds of early-life LD, including within the normal range of gestation length for Thoroughbred foals. Further work is required to elucidate biological mechanisms behind this association. [ABSTRACT FROM AUTHOR]

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

The Jeju horse is a native Korean species that has been breeding on Jeju Island since the 13th century. Their shape has a distinct appearance from the representative species, Thoroughbred. Here, we performed a comparison of the Jeju horse and Thoroughbred horse for the identification of genome-wide structure variation by using the next-generation sequencing (NGS) technique. We generated an average of 95.59 Gb of the DNA sequence, resulting in an average of 33.74 X sequence coverage from five Jeju horses. In addition, reads obtained from WGRS data almost covered the horse reference genome (mapped reads 98.4%). Based on our results, we identified 1,244,064 single nucleotide polymorphisms (SNPs), 113,498 genomic insertions, and 114,751 deletions through bioinformatics analysis. Interestingly, the results of the WGRS comparison indicated that the eqCD1a6 gene contains signatures of positive natural selection in Jeju horses. The eqCD1a6 gene is known to be involved in immunity. The eqCD1a6 gene of Jeju horses commonly contained 296 variants (275 SNPs and 21 INDELs) that were compared with its counterpart of two Thoroughbred horses. In addition, we used LOAA, digital PCR, to confirm the possibility of developing a molecular marker for species identification using variant sites. As a result, it was possible to confirm the result of the molecular marker with high accuracy. Nevertheless, eqCD1a6 was shown to be functionally intact. Taken together, we have found significant genomic variation in these two different horse species.

Clenbuterol, the β2-adrenoceptor agonist, is gaining growing popularity because of its effects on weight loss (i.e., chemical liposuction). It is also popular in bodybuilding and professional sports, due to its effects that are similar to anabolic steroids. However, it is prohibited by anti-doping control. On the other hand, it is suggested that clenbuterol can inhibit the inflammatory process. The cells from 14 untrained and 14 well-trained race horses were collected after acute exercise and cultured with clenbuterol. The expressions of CD4, CD8, FoxP3, CD14, MHCII, and CD5 in PBMC, and reactive oxygen species (ROS) production, as well as cell proliferation, were evaluated by flow cytometry. In addition, IL-1β, IL-4, IL-6, IL-10, IL-17, INF-γ and TNF-α concentrations were evaluated by ELISA. β2-adrenoceptor stimulation leads to enhanced anti-inflammatory properties in well-trained horses, as do low doses in untrained animals. In contrast, higher clenbuterol doses create a pro-inflammatory environment in inexperienced horses. In conclusion, β2-adrenoceptor stimulation leads to a biphasic response. In addition, the immune cells are more sensitive to drug abuse in inexperienced individuals under physical training.

This study investigated the effects of six weeks of normobaric hypoxic training on transcriptional expression of the genes associated with mitochondrial and glycolytic activities in Thoroughbred horses. Eight horses were divided into two groups of four. They completed an identical incremental, moderate intensity training program, except that one group trained in a hypoxic chamber with 15% oxygen for 30 min on alternate days except Sundays (HT), while the other group trained in normal air (NC). Prior to and post training, heart rate and blood lactate were measured during an incremental treadmill test. Muscle biopsy samples were taken prior to and 24 h post the training period for qPCR analysis of mRNA changes in VEGF, PPARγ, HIF-1α, PGC-1α, COX4, AK3, LDH, PFK, PKm and SOD-2. No significant differences between the HT and NC were detected by independent-samples t-test with Bonferroni correction for multiple comparisons (P>0.05) in relative changes of mRNA abundance. There were no significant differences between groups for heart rate and blood lactate during the treadmill test. The outcomes indicated that this hypoxia training program did not cause a significant variation in basal level expression of the selected mRNAs in Thoroughbreds as compared with normoxic training.

This study aimed to assess Australian veterinarians' knowledge, perceptions and treatment strategies for worm control in horses with an online questionnaire. The questionnaire comprised 64 questions covering various aspects of: (i) veterinary practice; (ii) the veterinarian's knowledge of gastrointestinal nematodes (GINs) and the importance of parasites in different age groups of horses; (iii) the diagnosis and control of worms; (iv) anthelmintics and anthelmintic resistance (AR); (v) grazing management; and (vi) the means of communication and the discussion between veterinarians and their clients regarding worm control. Following a pilot survey, a link for the questionnaire survey was sent to all ( n = 1,148) registered members of Equine Veterinarians Australia in April 2020. The response rate for the questionnaire was 10% (118 of 1,148). The findings of this study illustrate veterinarians' good understanding of aspects of equine parasites, including control. However, respondents mainly recommended frequent, interval-based prophylactic deworming in young horses, and only 40% (96 of 239) diagnosed GIN infections based on faecal egg count (FEC) results in all age groups of horses. Furthermore, only 27% (88 of 330) of the respondents made deworming decisions based on FECs. Most of the respondents recommended macrocyclic lactones (MLs) for all age groups of horses (71%, 481 of 677), and the most frequently used method to calculate the dose of anthelmintics was by estimating the weight of animals visually (53%, 63 of 118). Although the majority of respondents (97%, 115 of 118) perceived AR to be a critical issue in managing worms in horses, 58% (67 of 118) of them were unaware of the status of AR on their clients' properties. Forty-two percent (50 of 118) of the respondents perceived the presence of AR in worms, including pinworms (16%), strongylins (15%), species of Draschia and Habronema (6%), Strongyloides westeri (2%) and tapeworms (1%). Twenty-seven percent (32 of 118) of the respondents rarely discussed equine worm control practices with their clients. This study provides insights into the perception and worm control practices recommended by Australian veterinarians to manage equine parasites. The findings highlight the importance of continued education and awareness of AR, and the use of non-chemical methods as well as consideration of the legislation of prescription-only use of anthelmintics based on FECs to achieve sustainable control of GINs in Australian horses., Competing Interests: The authors of this manuscript are members of the Australian Equine Parasitology Advisory Panel (AEPAP), including Abdul Jabbar, Ghazanfar Abbas, Jenni Bauquier, Charles El-Hage, Abdul Ghafar and Ian Beveridge (The University of Melbourne), Anne Beasley (University of Queensland), Kristopher Hughes (Charles Sturt University), Caroline Jacobson and Emma McConnell (Murdoch University), Edwina Wilkes (Racing Victoria), Peter Carrigan and Lucy Cudmore (Scone Equine Hospital) and John Hurley (Swettenham Stud). Boehringer Ingelheim supported the panel. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision., (Copyright © 2023 Abbas, Stevenson, Bauquier, Beasley, Jacobson, El-Hage, Wilkes, Carrigan, Cudmore, Hurley, Beveridge, Nielsen, Hughes and Jabbar.)

Catastrophic musculoskeletal injuries (CMI) in horses are associated with both too little and too much high-speed exercise. In order to advise trainers on training and management strategies that minimize the risk of musculoskeletal injury (MSI), a better understanding of how training practices affect MSI in racehorses is needed. Data from prospective studies relating training data and MSI are complicated by the gradual development of pathology and the effect of this on the ability of horses to train consistently prior to the identification of an injury. To circumvent this, 66 Australian Thoroughbred trainers were surveyed on their intended training practices, including rest, pre-training, and race-fit practices. Associations between intended training practices and catastrophic and non-catastrophic race day MSI outcomes in two-year-old and mature (≥three-year-old) horses were assessed using multivariable negative binomial regression models. The incidence of two-year-old race day MSI was lower for trainers who preferred shorter times (weeks) to trial, less time in fast work pre-trial ( p  = 0.003), shorter, more frequent rest periods ( p  < 0.01) and higher amounts of fast work at 15.5-16.7 m/s once race-fit ( p  = 0.001). The incidence of mature horse race day MSI was lower for trainers who preferred longer rest periods ( p  = 0.026) and a high-volume pre-trial training strategy comprising a high volume of slower speed gallop training and longer times to trial compared to fast and light training programs ( p  = 0.004) for their mature horses, in addition to higher amounts of fast work at 15.5-16.7 m/s for their race-fit two-year-olds ( p  = 0.012). Race day CMI incidence was lower for trainers who preferred lower volumes of fast gallop work for their race-fit mature horses ( p  < 0.05). These results suggest that two-year-old training practices could affect MSI risk later in a horse's career, and that age and stage in training (pre-trial, race-fit) are important considerations when developing training practices to minimize the risk of MSI., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Wong, Morrice-West, Hitchens and Whitton.)

Worldwide, musculoskeletal injuries remain a major problem for the Thoroughbred racing industry. There is a strong interest in developing training and management strategies to reduce the impact of musculoskeletal injuries, however, progress has been limited by studies reporting conflicting findings, and a limited understanding of the role of different training methods in preventing injury. There is little data on patterns of rest periods and exercise data and how these vary between trainers. This prospective study of two-year-old racehorses was conducted in Queensland, Australia and involved weekly personal structured interviews with 26 trainers over 56 weeks. Detailed daily exercise data for 535 horses providing 1258 training preparations and 7512 weeks at risk were collected. Trainers were categorised into three groups by the mean number of two-year-old horses that they had in work each week over the study duration: (1) Small stables with five or less, (2) Medium stables with 6 to 15 and (3) Large stables with greater than 15 horses in training. Differences between trainers with small, medium and large stable sizes were evaluated using linear regression, Kruskal–Wallis equality-of-populations rank test if linear models were mis-specified or Chi-squared tests for categorical variables. Significant differences were observed between trainers, with horses from larger stables accumulating a greater high-speed exercise volume (p < 0.001), attaining training milestones more frequently (p = 0.01) and taking less time to reach their training milestones (p = 0.001). This study provides detailed data to which training practices from other locations can be compared. Presenting actual training data rather than trainers’ estimation of a typical program provides a more accurate assessment of training practices. Understanding how training practices vary between regions improves comparability of studies investigating risk factors and is an important step towards reducing the impact of musculoskeletal injuries.

There is international public concern regarding retirement of racehorses, including the reason for retirement and the outcome for horses after racing. However, there are currently no prospective studies investigating these factors. A recent independent inquiry in Queensland, Australia, highlighted that the true outcomes for horses after retirement from racing are largely unknown. Furthermore, there are currently no measures to monitor the outcome for racehorses and their welfare once they have left the care of the trainer. This study investigated these gaps in knowledge through a weekly survey conducted over a 13-month period. We aimed to evaluate: (1) the incidence of retirement, (2) the reasons and risk factors for retirement and (3) the medium-term (greater than 6 months) outcomes for horses after retirement. Data were collected through personal structured weekly interviews with participating trainers and analysed using negative binomial and logistic regression. There was a low incidence of retirements, namely 0.4% of horses in training per week. The season and training track did not affect the incidence of retirement. Musculoskeletal injuries were the most common reason for retirement (40/110 horses, 36%). Involuntary retirements accounted for 56/100 (51%) of retirements, whereby musculoskeletal injuries, respiratory or cardiac conditions and behavioural problems prevented the horse from racing The odds of voluntary retirement, whereby the horse was retired due to racing form or impending injury, increased with each additional race start (OR 1.05; p = 0.01) and start/year of racing (OR 1.21; p = 0.03) but decreased with increasing percentage of first, second and third places (OR 0.94; p < 0.001). Medium-term follow-up (median 14 months, IQR 11, 18, range 8–21) revealed that most horses (108/110; 98%) were repurposed after retirement, almost half as performance horses (50/110; 46%). Horses that voluntarily retired had 2.28 times the odds of being repurposed as performance horses than those retired involuntarily (p = 0.03). Whether retirement was voluntary or involuntary did not influence whether horses were used for breeding or pleasure. The primary limitation of this study is that our results reflect retirement in racehorses in South East Queensland, Australia, and may not be globally applicable. Furthermore, we were unable to monitor the long-term outcome and welfare of horses in their new careers. It is vital that the industry is focused on understanding the risks for voluntary rather than involuntary retirement and optimising the long-term repurposing of horses. There is a need for traceability and accountability for these horses to ensure that their welfare is maintained in their new careers.

Musculoskeletal injuries (MSI) continue to affect Thoroughbred racehorses internationally. There is a strong interest in developing training and management strategies to reduce their impact, however, studies of risk factors report inconsistent findings. Furthermore, many injuries and fatalities occur during training rather than during racing, yet most studies report racing data only. By combining racing and training data a larger exposure to risk factors and a larger number of musculoskeletal injuries are captured and the true effect of risk factors may be more accurately represented. Furthermore, modifications to reduce the impact of MSI are more readily implemented at the training level. Our study aimed to: (1) determine the risk factors for musculoskeletal injuries and whether these are different for two-year-old and older horses and (2) determine whether risk factors vary with type of injury. This was performed by repeating analyses by age category and injury type. Data from 202 cases and 202 matched controls were collected through weekly interviews with trainers and analysed using conditional logistic regression. Increasing dam parity significantly reduced the odds of injury in horses of all age groups because of the effect in two-year-old horses (odds ratio (OR) 0.08; 95% confidence interval (CI) 0.02, 0.36; p < 0.001). Increasing total preparation length is associated with higher odds of injury in horses of all ages (OR 5.56; 95% CI 1.59, 19.46; p = 0.01), but particularly in two-year-old horses (OR 8.05; 95% CI 1.92, 33.76; p = 0.004). Increasing number of days exercised at a slow pace decreased the odds of injury in horses of all ages (OR 0.09; 95% CI 0.03, 0.28; p < 0.001). The distance travelled at three-quarter pace and above (faster than 13 m/s; 15 s/furlong; 800 m/min; 48 km/h) and the total distance travelled at a gallop (faster than 15 m/s; 13 s/furlong; 900 m/min; 55 km/h) in the past four weeks significantly affected the odds of injury. There was a non-linear association between high-speed exercise and injury whereby the odds of injury initially increased and subsequently decreased as accumulated high-speed exercise distance increased. None of the racing career and performance indices affected the odds of injury. We identified horses in this population that have particularly high odds of injury. Two-year-old horses from primiparous mares are at increased odds of injury, particularly dorsal metacarpal disease. Two-year-old horses that have had a total preparation length of between 10 and 14 weeks also have increased odds of injury. Horses of all ages that travelled a total distance of 2.4–3.8 km (12–19 furlongs) at a gallop in the last four weeks and horses three years and older that travelled 3.0–4.8 km (15–24 furlongs) at three-quarter pace and above also have increased odds of injury. We recommend that these horses should be monitored closely for impending signs of injury. Increasing the number of days worked at a slow pace may be more effective for preventing injury, if horses are perceived at a higher risk, than resting the horse altogether. Early identification of horses at increased risk and appropriate intervention could substantially reduce the impact of musculoskeletal injuries in Thoroughbred racehorses.

Exercise significantly affects the body of both animals and humans, including the composition of the digestive microbiome. This study aimed to determine the changes in the composition of the most numerous bacterial phyla (Firmicutes and Bacteroidetes, as well as the level of the Lactobacillaceae family) in the digestive system of horses under the influence of physical effort. The study included a group of 17 Thoroughbred racehorses at the age of 3 years, fed the same forage, from whom feces samples were collected individually before and 48 h after physical effort. The obtained samples were subjected to DNA isolation and RT-PCR analysis. The results showed a significant increase in the level of both phyla after exercise compared to the state before physical effort; there were no such differences in the level of facultative aerobes, i.e., the Lactobacillaceae family (although a decreasing tendency was found after exercise). In addition, the analysis of the level of the studied phyla indicates individual differences in horses’ response to the effort.

Tongue Ties (TTs) are devices used to fixate the tongue to the mandible and hold it in this position during exercise with the goal of facilitating control of the horse and as a conservative treatment for dorsal displacement of the soft palate (DDSP). They have been used in racehorses for over 100 years. The conflicting evidence of its efficacy at preventing DDSP, combined with public concerns of potential welfare implications, have led to the banning of TTs by the Fédération Equestre Internationale (FEI) in 2004. However, TTs are still approved for use in racing in many countries. Their use is documented during racing by their racing authorities, but not in Thoroughbred (Direktorium für Vollblutzucht und Rennen, DVR) and Standardbred (Hauptverband für Traberzucht, HVT) racehorses in Germany. The prevalence of TT use is about 5 % in racehorses in Great Britain, increasing to up to 89 % of horses with a diagnosis of DDSP. Therefore, they are used very commonly and often in combination with other equipment. The objective of this study was to collect casuistic data on their use during training and racing in Germany. Data of 499 Thoroughbred racehorses were collected by sending questionnaires to 153 Thoroughbred trainers registered at the German racing authority (DVR). In addition, data of 82 Standardbreds were collected from 9 trainers. Of these 581 horses, 133 participated in international racing, while the others were trained for national races. Trainers were asked for their reasons to use TTs in training and racing, expected and seen changes by their use, material and fixation time of the tongue strap, the occurrence, frequency and characteristics of negative side effects. Overall, 17.2 % of all horses were trained and 19.3 % were started using TTs. Young 3- and 4 year old Standardbreds were trained more often using TTs than Thoroughbreds, while more Thoroughbreds than Standardbreds 5 years and older wore TT during training and racing. The most common fixation time of the tongue was 20 minutes. Most trainers used elastic nylons (22/35), while leather straps (7/35), cotton (2/35) and elastic (14/35) were less common. Positive effects most commonly reported by trainers were inhibition of tongue displacement over the bit (37/41) and reduction of respiratory noise (24/41). The majority also reported improved exercise performance in training (63 %) and racing (76 %). A slight majority of 22/41 trainers reported no adverse effects associated with the use of TT, while the others described negative effects in up to 10 % of applications (14/41) or even more than 12 % (5/41). The most common adverse reactions here were discoloration of the tongue under fixation (n = 16) followed by bleeding (n = 4) and paralysis (n = 1). In conclusion, despite common use and positive effects reported by Thoroughbred and Standardbred trainers, the application of a TT seems to impair animal welfare in a number of racehorses. The use of TTs was outlawed in Thoroughbred racing in June 2018 in Germany, but is still allowed for Standardbreds by the racing authorities. The results of our study might provide objective evidence for future decisions by the racing authorities in Germany. [ABSTRACT FROM AUTHOR]

Actinobacillus species are known to be pathogenic to horses. To clarify etiological agents of actinobacillosis in Japanese adult horses, 27 isolates from Japanese Thoroughbred racehorses putatively identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry as Actinobacillus were further identified by PCR of the A. equuli toxin gene, by CAMP test, and by 16S rRNA sequencing analysis. Actinobacillus equuli subsp. haemolyticus was isolated most frequently (16/27) and was related to respiratory infections. Actinobacillus equuli subsp. equuli (4/27) was isolated from chronic cases or concomitant with other bacterial infections. The remainder were A. pleuropneumoniae, unclassified Actinobacillus species and Pasteurella caballi. Actinobacillus equuli including subsp. haemolyticus and subsp. equuli were the species most frequently isolated from equine actinobacillosis in Japan. [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]

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

The equine first premolar is now considered a vestigial tooth that does not play a role in mastication. For centuries, this tooth has been blamed for a number of abnormalities. Given its anatomical location, the tooth is often implicated by riders to cause biting issues. Treatment of this tooth is considered controversial, with some clinicians extracting all equine first premolars prior to bit introduction and others choosing to remove only those shown to cause bite-related problems. In a private veterinary hospital in Lexington, Kentucky, dental charts of 306 Thoroughbred yearlings, average age 14.73 months (range: 8-22.7 months), were reviewed. In this group, 72.9% of horses, average age 14.99 months, had erupted first premolars at the time of the examination. This percentage increased with age, and by 18 months, 90% of Thoroughbred yearlings had erupted maxillary first premolars. Sexual dimorphism is present in the study group, as significantly fewer males than females have first premolars at 67.4% and 77.6%, respectively, P ≤.05. Mandibular and supernumerary first premolars are rarely reported in the literature and were not present in this group, suggesting they may erupt at a later age or are less common in Thoroughbreds. Maxillary first premolars are common in Thoroughbred yearlings and continue to erupt to 18 months of age in this breed, later than previously reported in some text. [ABSTRACT FROM AUTHOR]

Prion diseases are fatal neurodegenerative diseases characterised by the accumulation of an abnormal prion protein isoform (PrPSc), which is converted from the normal prion protein (PrPC). Prion diseases have been reported in an extensive number of species but not in horses up to now; therefore, horses are known to be a species resistant to prion diseases. The prion-like protein gene (PRND) is closely located downstream of the prion protein gene (PRNP) and the prion-like protein (Doppel) is a homologue with PrP. Previous studies have shown that an association between prion diseases and polymorphisms of the PRND gene is reported in the main hosts of prion diseases. Hence, we examined the genetic variations of the PRND gene in Thoroughbred horses. Interestingly, polymorphisms of the PRND gene were not detected. In addition, we conducted a comparative analysis of the amino acid sequences of the PRND gene to identify the differences between horses and other species. The amino acid sequence of the horse PRND gene showed the highest identity to that of sheep (83.7%), followed by that of goats, cattle and humans. To the best of our knowledge, this is the first genetic study of the PRND gene in horses. [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]

This study focused on 8 Thoroughbred racehorses showing bone marrow oedema-type signal in the proximal sagittal groove of the proximal phalanx, with the aim of understanding its clinical significance. Standing magnetic resonance imaging played an important role in assessing osseous abnormalities that were not radiographically identifiable. Further, a histopathological result from one of the cases showed there was oedema surrounding adipose tissues with increase in density of trabecular scaffolding. This may indicate presence of osseous injury within the area of decreased elasticity due to subchondral bone modeling. This study suggests that detection of osseous abnormality based on bone marrow oedema-type signal, and application of appropriate care following injury would contribute to prevent deterioration of stress-related fractures of the proximal phalanx. [ABSTRACT FROM AUTHOR]

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

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

Equid herpesvirus type 1 is primarily a respiratory tract virus associated with poor athletic performance that can also cause late gestation abortion, neonatal foal death and encephalomyelopathy. Horizontal transmission is well described, whereas evidence of vertical transmission of equid herpesvirus type 1 associated with the birth of a healthy foal has not been demonstrated. This study sampled a population of Thoroughbred mares (n = 71), and their healthy neonatal foals and foetal membranes, to test for the presence of both equid herpesvirus types 1 and 4 using a quantitative polymerase chain reaction assay. Foetal membrane swabs and tissue samples were taken immediately post-partum, and venous blood samples and nasal swabs were obtained from both mare and foal 8 h after birth. Neither equid herpesvirus type 1 nor equid herpesvirus type 4 nucleic acid was detected in any sample, and it was concluded that there was no active shedding of equid herpesvirus types 1 and 4 at the time of sampling. Consequently, no evidence of vertical transmission of these viruses could be found on this stud farm during the sampling period. [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]

The Jeju horse is an indigenous Korean horse breed that is currently registered with the Food and Agriculture Organization of the United Nations. However, there is severe lack of genomic studies on Jeju horse. This study was conducted to investigate genetic characteristics of horses including Jeju horse, Thoroughbred and Jeju crossbred (Jeju × Thoroughbred) populations. We compared the genomes of three horse populations using the Equine SNP70 Beadchip array. Short-range Linkage disequilibrium was the highest in Thoroughbred, whereas r2 values were lowest in Jeju horse. Expected heterozygosity was the highest in Jeju crossbred (0.351), followed by the Thoroughbred (0.337) and Jeju horse (0.311). The level of inbreeding was slightly higher in Thoroughbred (− 0.009) than in Jeju crossbred (− 0.035) and Jeju horse (− 0.038). FST value was the highest between Jeju horse and Thoroughbred (0.113), whereas Jeju crossbred and Thoroughbred showed the lowest value (0.031). The genetic relationship was further assessed by principal component analysis, suggesting that Jeju crossbred is more genetically similar to Thoroughbred than Jeju horse population. Additionally, we detected potential selection signatures, for example, in loci located on LCORL/NCAPG and PROP1 genes that are known to influence body. Genome-wide analyses of the three horse populations showed that all the breeds had somewhat a low level of inbreeding within each population. In the population structure analysis, we found that Jeju crossbred was genetically closer to Thoroughbred than Jeju horse. Furthermore, we identified several signatures of selection which might be associated with traits of interest. To our current knowledge, this study is the first genomic research, analyzing genetic relationships of Jeju horse, Thoroughbred and Jeju crossbred. [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]

The aim of the study was to examine the factors affecting longevity (as the number of years spent in race) in the Hungarian Thoroughbred horse population, and to investigate the total earnings won during lifetime and per start. The performance data was collected from 3,029 Thoroughbred horses (1,704 female, 1,674 male) born between 1996 and 2018 in Hungary with full known racing career. A multivariate generalized linear model was used to estimate the effect of sex of the horses, age at first start and the month of birth to longevity, expressed by the number of starts and years spent in race. Age of the horses at first start had a significant effect on the years spent in race, thereafter the model was dissected into age groups initiating a more accurate research. This showed that birth month also have a momentous effect on the examined traits in case of 2-year-old horses. Age of the horses at first start also affected the lifetime earnings. Sex of the horses had no effect on longevity in 2-year olds however, males are more likely to race because female horses tend to win less money. [ABSTRACT FROM AUTHOR]

The ACOX1 gene encodes peroxisomal acyl-coenzyme A oxidase 1, the first enzyme in the fatty acid β-oxidation pathway, which could be significant for organisms exposed to long periods of starvation and harsh living conditions. We hypothesized that variations within ACOX1, revealed by RNA Sequencing (RNA-Seq), might be based on adaptation to living conditions and had resulted from selection pressure. There were five different horse breeds used in this study, representing various utility types: Arabian, Thoroughbred, Polish Konik, draft horses, and Hucul. The single-nucleotide polymorphism (SNP) located in the ACOX1 (rs782885985) was used as a marker and was identified using the PCR restriction fragment length polymorphism method (PCR-RFLP). Results indicated extremely different genotype and allele distributions of the ACOX1 gene across breeds. A predominance of the G allele was exhibited in horses that had adapted to difficult environmental conditions, namely, Polish Konik and Huculs, which are considered to be primitive breeds. The prevalence of the T allele in Thoroughbreds indicated that ACOX1 is significant in energy metabolism during flat racing.

Despite over three decades of active research, musculoskeletal injuries (MSI) remain a global problem for the Thoroughbred (TB) racing industry. High-speed exercise history (HSEH) has been identified as an important risk factor for MSI. However, the nature of this relationship remains unclear, with an apparent protective effect of HSE against injury, before it becomes potentially harmful. Many MSI cases and fatalities occur during training rather than during racing, resulting in an underestimation of injury from studies focused on race day. The objective of this study was to examine the current evidence of the effect of combined training and racing HSEH on MSI in TB flat racehorses, through a systematic review and meta-analysis. A systematic search of the relevant literature was performed using PubMed®, Scopus®, Web of Science®, and Embase® online databases and the gray literature using sites containing “.edu” or “.edu.au”. Studies included in the review had explored seven different measures of HSE, including total career HSE distance, cumulative HSE distance in the 30 and 60 days before MSI, average HSE distance per day, per event and per 30 days, and the total number of HSE events. The total cumulative career HSE distance significantly affected the odds of MSI, with every 5-furlong increase, the odds of MSI increased by 2% (OR = 1.02; 95% CI 1.01, 1.03; p = 0.004). The average HSE distance per day also affected the odds of MSI, with every additional furlong increasing the odds of MSI by 73% (OR = 1.73; 95% CI 1.29, 2.31; p < 0.001). Other measures of HSE were not found to be consistently associated with risk of MSI, but these results should be interpreted with caution. Significant methodological limitations were identified and influence the comparability of studies. Standardizing the measures of HSE in studies of MSI, and describing training conditions in more detail, would support a more thorough investigation of the relationship between HSE and MSI. An improved understanding of this relationship is critical to mitigating the impact of MSI in the Thoroughbred racehorse.

Thoroughbred jump racing sits in the spotlight of contemporary welfare and ethical debates about horse racing. In Australia, jump racing comprises hurdle and steeplechase races and has ceased in all but two states, Victoria and South Australia. This paper documents the size, geography, composition, and dynamics of Australian jump racing for the 2012, 2013, and 2014 seasons with a focus on debate about risks to horses. We found that the majority of Australian jump racing is regional, based in Victoria, and involves a small group of experienced trainers and jockeys. Australian jump horses are on average 6.4 years of age. The jump career of the majority of horses involves participating in three or less hurdle races and over one season. Almost one quarter of Australian jump horses race only once. There were ten horse fatalities in races over the study period, with an overall fatality rate of 5.1 fatalities per 1000 horses starting in a jump race (0.51%). There was significant disparity between the fatality rate for hurdles, 0.75 fatalities per 1000 starts (0.075%) and steeplechases, 14 fatalities per 1000 starts (1.4%). Safety initiatives introduced by regulators in 2010 appear to have significantly decreased risks to horses in hurdles but have had little or no effect in steeplechases. Our discussion considers these Animals 2015, 5 1073 data in light of public controversy, political debate, and industry regulation related to jump horse safety.