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

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

Simple Summary: Mitigating the risk of catastrophic injuries in the horse racing industry remains a challenge. Non-invasive methods such as CT imaging in combination with machine learning could be used to screen horses at risk of injury, but there remain questions on the feasibility of such an approach. In this work, we investigated whether machine learning models could be developed from in vitro harvested μCT images of intact proximal sesamoid bones to predict whether the bone was from a horse that suffered a catastrophic injury or from a control group. The average accuracy in differentiating whether a sesamoid bone came from a case or control horse using our approach was 0.754. Our work suggests it may be possible to develop similar models using CT images of horses in the clinical setting. Proximal sesamoid bone (PSB) fractures are the most common musculoskeletal injury in race-horses. X-ray CT imaging can detect expressed radiological features in horses that experienced catastrophic fractures. Our objective was to assess whether expressed radiomic features in the PSBs of 50 horses can be used to develop machine learning models for predicting PSB fractures. The μCTs of intact contralateral PSBs from 50 horses, 30 of which suffered catastrophic fractures, and 20 controls were studied. From the 129 intact μCT images of PSBs, 102 radiomic features were computed using a variety of voxel resampling dimensions. Decision Trees and Wrapper methods were used to identify the 20 top expressed features, and six machine learning algorithms were developed to model the risk of fracture. The accuracy of all machine learning models ranged from 0.643 to 0.903 with an average of 0.754. On average, Support Vector Machine, Random Forest (RUS Boost), and Log-regression models had higher performance than K-means Nearest Neighbor, Neural Network, and Random Forest (Bagged Trees) models. Model accuracy peaked at 0.5 mm and decreased substantially when the resampling resolution was greater than or equal to 1 mm. We find that, for this in vitro dataset, it is possible to differentiate between unfractured PSBs from case and control horses using μCT images. It may be possible to extend these findings to the assessment of fracture risk in standing horses. [ABSTRACT FROM AUTHOR]

There are almost 9,500 full-time employees in Australia's thoroughbred horse breeding industry. During foaling, they can be exposed to bodily fluids and mucous membranes which may present risks for zoonotic disease. These risks can be mitigated through personal biosecurity strategies. The aim of this study was to identify which personal biosecurity strategies were more or less likely to be adopted by workers. Seventeen participants representing 14 thoroughbred breeding farms and three equine veterinary practices in Australia's largest thoroughbred breeding region trialed up to 16 stakeholder-nominated personal biosecurity strategies over the 2021 foaling season. The strategies encompassed personal protective equipment (PPE), zoonotic disease awareness, policies and protocols, supportive environments, and leadership. Strategy adoption was monitored through three repeated self-audit surveys designed around the Transtheoretical Model of change (TTM) and findings were reviewed in exit interviews. For all survey waves in aggregate, 13 strategies were practiced by at least 50.0% of participants. Participants were most likely to use a ready-made foaling box (98.0%), communicate the message that PPE usage is a personal responsibility (94.1%) and use ready-made PPE kits (88.2%). However, 31.4% had no intention of doing practice sessions and/or dummy runs for PPE use and 27.5% had no intention of using a buddy system on farm/practice to check use of PPE. Whilst these rates indicate workers' willingness to adopt and maintain personal biosecurity strategies, they also indicate capacity for more practices to be implemented more often. Overall, the findings highlight the need for personal biosecurity interventions to be sensitive to the demands of the annual thoroughbred breeding calendar, the size of the breeding operation and the availability of skilled staff.

Simple Summary: Multiple pregnancies (MPs), or twins/triplets, are commonly diagnosed in pregnant mares. Whilst some studies have identified factors associated with an increased risk of MPs, they have only looked at each factor individually and not accounted for the effects of factors when they occur together. This study used statistical modelling to identify risk factors for MPs, looking at 27 factors as well as the contribution of the mare, stallion (both proxies for genetics), farm, and veterinarian. We found that multiple ovulations and the use of a drug that mimics prostaglandin F2α to induce oestrus, both increased the risk of a mare having an MP. Mares that had a foal that same year, had a uterine cyst, or who did not get pregnant on the first cycle they were bred on were at a decreased risk of having an MP. Factors that impact the early embryonic environment are more important influences of multiple pregnancies when compared to the genetics of the mare. The increased incidence of MP but not MOs over the previous decades may well reflect improved management of the endometrium as opposed to selection of mares with increased risk for MPs. A limitation of the study is the reliance on clinical records being completed accurately. Multiple pregnancies (MPs) are commonly diagnosed during breeding management of mares. Whilst some studies have reported on factors associated with the risk of MPs, few have utilised multivariable data analysis to control for confounding variables. A prospective cohort study of Thoroughbred broodmares was conducted with information collected on 27 factors. Mixed-effects logistic regression was used to determine risk factors for MPs. Mare, stallion, stud, and veterinarian were evaluated as random effects. The prevalence of MPs in 1754 mares and 2245 pregnancies was 16.06% (95% confidence interval [CI] = 14.54, 17.58). Multiple ovulations (OR = 15.57, 95% CI = 11.88, 20.53) and treatment with cloprostenol (OR = 1.35, 95% CI = 1.015, 1.80) were associated with increased odds of MPs following multivariable analysis. Mares that foaled at the start of the breeding season (OR = 0.66, 95% CI = 0.47, 0.94), conceived at the second or more oestrus cycles (OR = 0.60, 95% CI= 0.43, 0.84), or identified with a uterine cyst (OR = 0.63, 95% CI = 0.40, 0.97) were at reduced odds of conceiving MPs. Mare, stallion, stud, and veterinarian were not associated with MPs. These findings provide possible explanations as to why the prevalence of MPs but not MOs have increased over the last decade. [ABSTRACT FROM AUTHOR]

Proximal sesamoid bone (PSB) fractures are the most common musculoskeletal injury in race-horses. X-ray CT imaging can detect expressed radiological features in horses that experienced catastrophic fractures. Our objective was to assess whether expressed radiomic features in the PSBs of 50 horses can be used to develop machine learning models for predicting PSB fractures. The μCTs of intact contralateral PSBs from 50 horses, 30 of which suffered catastrophic fractures, and 20 controls were studied. From the 129 intact μCT images of PSBs, 102 radiomic features were computed using a variety of voxel resampling dimensions. Decision Trees and Wrapper methods were used to identify the 20 top expressed features, and six machine learning algorithms were developed to model the risk of fracture. The accuracy of all machine learning models ranged from 0.643 to 0.903 with an average of 0.754. On average, Support Vector Machine, Random Forest (RUS Boost), and Log-regression models had higher performance than K-means Nearest Neighbor, Neural Network, and Random Forest (Bagged Trees) models. Model accuracy peaked at 0.5 mm and decreased substantially when the resampling resolution was greater than or equal to 1 mm. We find that, for this in vitro dataset, it is possible to differentiate between unfractured PSBs from case and control horses using μCT images. It may be possible to extend these findings to the assessment of fracture risk in standing horses.

Multiple pregnancies (MPs) are commonly diagnosed during breeding management of mares. Whilst some studies have reported on factors associated with the risk of MPs, few have utilised multivariable data analysis to control for confounding variables. A prospective cohort study of Thoroughbred broodmares was conducted with information collected on 27 factors. Mixed-effects logistic regression was used to determine risk factors for MPs. Mare, stallion, stud, and veterinarian were evaluated as random effects. The prevalence of MPs in 1754 mares and 2245 pregnancies was 16.06% (95% confidence interval [CI] = 14.54, 17.58). Multiple ovulations (OR = 15.57, 95% CI = 11.88, 20.53) and treatment with cloprostenol (OR = 1.35, 95% CI = 1.015, 1.80) were associated with increased odds of MPs following multivariable analysis. Mares that foaled at the start of the breeding season (OR = 0.66, 95% CI = 0.47, 0.94), conceived at the second or more oestrus cycles (OR = 0.60, 95% CI= 0.43, 0.84), or identified with a uterine cyst (OR = 0.63, 95% CI = 0.40, 0.97) were at reduced odds of conceiving MPs. Mare, stallion, stud, and veterinarian were not associated with MPs. These findings provide possible explanations as to why the prevalence of MPs but not MOs have increased over the last decade.

Context. At pasture, the nutritional status of mares will change due to a dynamic association between their energy requirements and the energy supply. Change in the plane of nutrition can influence reproductive performance measures in the mares. To help optimise nutritional and operational management of mares on stud farms, the nutritional status of Thoroughbred broodmares and the factors influencing the energy supply and demand were investigated. Aims. To assess nutritional status of the Thoroughbred broodmare herds under 'normal' New Zealand commercial stud-farm conditions. Methods. The energy intake, energy requirement and energy balance during the last 3 months of pregnancy and the first 5 months of lactation were modelled for mares with an initial bodyweight of 450 kg, 500 kg, 550 kg and 600 kg, and foaled at 0, 15, 50, and 90 days after 1 September. Key results. For all foaling dates and bodyweights, mares were in positive energy balance during the last 3 months of pregnancy (6.1-8.5%). Energy balance decreased as pregnancy progressed, followed by a large and acute energy deficit that was initiated soon after foaling and continued during lactation. The energy deficit during lactation varied between -8.6% and -12.4%, depending on the foaling date modelled. Mares foaling later in the season (50-90 days after 1 September) had greater and longer (30-50 days) postpartum energy deficit than did mares that foaled earlier in the season, who recovered within 20 days postpartum. The modelled changes in the energy balance would be large enough to initiate mobilisation of the fat reserve (body condition), and could, therefore, explain the observation of delayed postpartum to conception interval observed with later-foaling mares on commercial farms. Conclusions. There is a large and prolonged energy deficit soon after foaling and throughout 150 days of lactation in Thoroughbred mares managed under New Zealand commercial grazing conditions. Foaling later in the season can cause a mismatch in energy supply and demand that would increase and prolong the energy deficit. Implications. These findings suggest a need for stud farms to actively manage the pasture supply and monitor the mare's BWT and BCS changes in an attempt to optimise the mare's nutritional status and reproductive performance. [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]

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]

Little is known about the types of surfaces used during training of Thoroughbred racehorses or methods of exercise used in addition to ridden track-work. Our aims were to (1) describe the types of surfaces used in the training of Thoroughbred racehorses and to (2) identify alternative approaches used to exercise horses in addition to, or in place of, ridden overground track-work. Information regarding surface and alternative exercise methods was collected as part of an in-person survey of training practices of 66 registered Thoroughbred trainers in Victoria, Australia. Sand and synthetic surfaces were used by 97% and 36% of trainers respectively for slow-workouts, with galloping on turf training tracks used in training regimens by 82% and synthetic by 58% of trainers. Of those trainers utilising turf tracks, only 34% of gallop training was completed on turf despite turf being the predominant racing surface. Almost 90% of trainers used alternatives to ridden exercise. There is substantial variation in training surface used and alternative types of exercise undertaken by Victorian trainers. Future research should focus on how such practices relate to injury risk, particularly as it relates to the importance of musculoskeletal adaptation to specific race-day surfaces.

Monitoring racehorse fatality and associated jockey falls provides benchmarks for intervention strategies. The aims of this study were to describe the incidence of and reasons for fatalities in Thoroughbred horses during flat races in the Australian Capital Territory and New South Wales (NSW), Australia, and to describe reported jockey falls and injuries associated with racehorse fatalities. A cohort study identified all racehorse fatalities reported through Racing NSW for the 2009–2010 to 2013–2014 racing seasons. Risks of racehorse fatality, fatal musculoskeletal injury, spontaneous death (as distinct from euthanasia) and racehorse fatality associated jockey falls and injuries were calculated using Poisson regression. A total of 167 horse fatalities were reported, with an overall incidence of 0.59 deaths/1000 starts. Forty-nine reasons for horse fatality were reported, although post-mortem examinations were conducted on only 52/165 (31.5%) horses. Musculoskeletal injury accounted for 144/167 (86.2%) fatalities, with an incidence of 0.52/1000 starts. Fractures comprised 96/167 (57.5%) fatalities, with the fetlock or proximal sesamoid bones being the most common fracture location, comprising 36/96 (37.5%) fractures. Only 22/166 (13.3%) racehorse fatalities were due to spontaneous death, representing an incidence of 0.08/1000 starts. A total of 50 racehorse fatality associated jockey falls were reported (incidence of 0.18/1000 starts), with 32 reported jockey injuries (incidence of 0.12/1000 starts). Most racehorse fatality associated jockey injuries occurred to the limbs (17/32, 53.1%), particularly the upper limb. The estimates for both horse fatality and associated jockey injury were comparable with previous estimates from other jurisdictions internationally. [ABSTRACT FROM AUTHOR]

The purpose of this study was to gain evidence on the prevalence of dental abnormalities in stable-kept horses in comparison with free-living horses. It is expected that free-living horses that graze for as much as 16 h/day will have fewer dental abnormalities than stable-kept horses. In this study, the latter group was fed a diet that was based on a relatively high-energy, cereal-based feed. This was thought to be a representative of common practice in domesticated, stable-kept horses. Compound diets such as this have previously been shown to increase the frequency of chewing cycles and decrease mediolateral excursion. The occurrence of 10 named dental abnormalities present in the dentition of 60 Thoroughbred-type horses was recorded. Half of the population was at grass all year round in New South Wales, Australia. The remainder were stabled for 24 h/day in Gloucestershire, UK. All horses were between 5 and 15 years of age. The same, experienced, equine dental technician examined all horses using a full-mouth speculum and produced a routine dental chart. Stable-kept horses had a significantly higher total occurrence of abnormalities (P < 0.001) than free-living horses. The stable-kept group had a significantly higher prevalence of exaggerated transverse ridging across the occlusal surface of the cheek teeth, focal or ramped overgrowths of the cheek teeth and periodontal disease (P < 0.01 in all cases). All horses in both groups had some occurrence of sharp edges of the buccal and lingual edges of the cheek teeth. The results are in agreement with anecdotal evidence that a fibre-based, grazed diet results in fewer dental abnormalities. However, sharp edges may occur even with what is perceived as a ‘natural’ diet.

• Speed, distance and time metrics tend to increase in accordance with level of play, also typically showing a concomitant reduction in variability • Women's Polo is comparable to 0– and 6–goal Polo, when comparing within-tournament measures and accompanying variability • Polo, irrespective of level, shows a high degree of between tournament variability. This is driven by within-subject variability which exceeded that of between-subject variability. • Z-scores are a convenient and useful method for capturing and displaying between tournament variability. This paper provides exemplar boundaries for practitioners considering this approach in Polo. The external work, as measured by global positioning systems, undertaken by Polo ponies during tournament play has been well-described across Polo of varying levels in both Open and Women's Polo. However, the variability within these data have not been thoroughly examined. Understanding the variability within these data between players (within-tournament variability) and between tournaments allows a deeper understanding of expected Polo performance and can inform coaching and tactical decisions, as well as aid in longitudinal horse development and comparison to other equestrian disciplines. The present paper captured data from 618 chukkas of Polo, in levels ranging from 0– to 16–goal and Women's Polo, across three New Zealand Polo seasons. Standard error and coefficient of variation were calculated to assess within-tournament variability; between-tournament variability was assessed via median percentage difference and Spearman's rho correlation coefficients. Playing duration, speeds (average and maximum) and distance metrics (total and standardized speed zones) typically increase with level of Polo play, with a concomitant reduction in within-tournament variability also seen. Nought (0–), 6–goal and Women's Polo show comparable within-tournament measures and associated variability. Polo, shows a high degree of between-tournament variability as within-player variability often exceeds that of between-player variability, affecting mathematical interpretations of reliability. Z-scores are a convenient alternative method for capturing and displaying between-tournament variability for the examined parameters, facilitating comparing across tournaments and seasons. Exemplar boundaries for this approach in Polo are provided. [ABSTRACT FROM AUTHOR]

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

An 8-year-old Thoroughbred mare presented with acute bilateral epistaxis. The mare showed no clinical signs other than cough and profuse bilateral epistaxis. Antibiotic therapy was instituted and a transtracheal wash was collected. Large numbers of inflammatory neutrophils and gram-positive cocci were reported in the tracheal wash. The antibiotic therapy was continued for 7 days at which time the mare appeared clinically normal. The mare was successfully bred and was confirmed pregnant. She was referred to a hospital when the epistaxis recurred. She was treated with another antibiotic, and thoracic radiographs were also taken which revealed a space occupying lesion. The mare foaled a live foal. She developed bilateral thickening of her limbs. The swellings were of boney consistency and affected all four legs, particularly the forelimbs. A diagnosis of pulmonary hypertrophic osteopathy was made. The mare was again sent for further investigation. The thoracic mass had increased in size from the first examination. A biopsy was collected by endoscopy which confirmed a neoplastic process. After deterioration in her condition, the mare was euthanized on humane grounds. An autopsy report revealed that the mare had approximately 80% of the left lung replaced by neoplastic tissue. The right lung contained many small nodular masses. There was an associated cardiomegaly. In this case, the development of periosteal proliferation in multiple metaphyses was secondary to an intrathoracic neoplastic mass. [ABSTRACT FROM AUTHOR]

Enhanced understanding of reasons for, and timings of, mortality in Thoroughbreds prior to entering race training is warranted to provide insight into this population's health status. The aims of this study were to describe pathologies diagnosed at post-mortem (PM) examination in Thoroughbreds aged from birth to 18 months and investigate associations between age and pathology. Reports from a pathology laboratory in Newmarket, UK, were used to identify eligible cases examined between January 2006 and December 2020. Reported pathologies were extracted and categorised where appropriate. Comorbidities and pathogens identified were reported where available. Associations between age and selected pathologies were assessed using logistic regression. Of 144 eligible Thoroughbreds presented for PM, 137 had an available report and pathologist's diagnosis. Congenital defects were most commonly reported (20%; n = 28/137; 95%CI 15–29), 69% of which (n = 19/28; 95%CI 49–82) were conformational manifestations of developmental orthopedic disease (DOD). Pneumonia was an important pathology (14%; n = 20/137; 95%CI 36–53) during the pre-weaning period, where Rhodococcus equi was identified in 50% (n = 10/20; 95% CI 29–70) of cases. Odds of congenital defects (OR 56.6; 95%CI 7.0–460.0; P < 0.001) were significantly greater in horses aged 0–2 days compared to 4–18 months at PM. Odds of pneumonia (OR 4.3; 95%CI 1.1–1.7; P = 0.04) were significantly greater in horses ages 1–4 months compared to 0–2 days at PM. This study shows that conformational manifestations of DOD are an important contributor to perinatal mortality, and that pathologies reported at PM vary with age in young Thoroughbreds. • Post-mortem findings from young Thoroughbreds are described. • The majority of cases presented in the neonatal period. • Congenital limb defects were an important contributor to perinatal mortality. • Rhodococcus equi was an important pathogen, particularly in pre-weaning pneumonia. [ABSTRACT FROM AUTHOR]

It has been observed that microbubbles may pass through the pulmonary circulation of dogs and humans during exercise. In humans, this phenomenon has been associated with lower pulmonary artery pressures, enhanced right ventricular function and greater exercise capacity. In the exercising Thoroughbred horse, extraordinarily high cardiac outputs exert significant pulmonary vascular stresses. The aim of this study was to determine, using contrast echocardiography, whether Thoroughbred horses performing strenuous exercise developed pulmonary transit of agitated contrast microbubbles (PTAC). At rest, agitated contrast was observed in the right ventricle, but not in the left ventricle. However, post-exercise microbubbles were observed in the left ventricle, confirming the occurrence of PTAC with exercise but not at rest. Further investigation is warranted to investigate whether this phenomenon may be associated with superior physiology and performance measures as has been implicated in other species. [ABSTRACT FROM AUTHOR]

Abstract: Stereotypies are considered a cause and symptom of impaired welfare, and have been associated with suboptimal husbandry systems. The aim of this study was to estimate the prevalence of stereotypic and other abnormal behaviors in Chilean thoroughbreds by direct observation, and examine their associations with biological characteristics and management practices. Seven hundred forty-three racehorses were observed directly, every 5 minutes during 1 hour before and after feeding, to identify behavioral disorders. A questionnaire was administered to handlers to obtain information about the animal and husbandry practices. The total observed prevalence rate of horses with one or more abnormal behavior was 11.03%. The total observed prevalence rates of stereotypies and abnormal behaviors were 6.32% and 5.52%, respectively. Horses at racetrack B presented more abnormal behaviors than those at racetrack A (P = .0092), and specifically, the prevalence of the oral group was higher (P = .0013). Mares presented a higher percentage of stereotypies (P = .0014), and the use of wood shaving bedding was positively associated with abnormal oral behaviors (P = .0027). Visual contact with conspecifics was possible for 86% of horses; the remaining had no social contact. Their diet consisted of a mixture of 71% of oats and 29% of roughage in average, presented between one and three times daily. No significant associations were found between the presence of visual contact, number of daily rations, yard, and percentage of roughage delivered, and stereotypy presentation (P > .05). In 43% of the cases with stereotypy, horses were impeded from performing the behavior by physical methods, avoiding the real problem and acting as a risk for animal welfare. [Copyright &y& Elsevier]

The dynamic behaviour of racetrack surfaces during hoof impact is a likely risk factor for racehorse injuries and fatalities. A track-testing device that simulates equine hoof impact was used to assess the effects of surface type (dirt, synthetic), surface depth (2, 3, 4 layers), test boundary area (929, 6,606, 11,381 cm), harrowing, and impact angle (0°, 20° from vertical) on dynamic surface properties. Surfaces were tested within a laboratory track-in-a-box. Surface type and depth, boundary area, and harrowing significantly affected dynamic surface properties during impacts ( P < 0.05). The synthetic surface was generally less stiff, and had 26-73% lower maximum impact forces and load rates, than the dirt surface. Harrowing decreased stiffness and differences between dirt and synthetic properties. Measured surface stiffness was larger for the smallest depth and boundary area, but most surface properties were not significantly different between the larger boundary areas. Surfaces were less stiff with angled impacts than vertical impacts. [ABSTRACT FROM AUTHOR]

The purpose of this study was to gain evidence on the prevalence of dental abnormalities in stable-kept horses in comparison with free-living horses. It is expected that free-living horses that graze for as much as 16 h/day will have fewer dental abnormalities than stable-kept horses. In this study, the latter group was fed a diet that was based on a relatively high-energy, cereal-based feed. This was thought to be a representative of common practice in domesticated, stable-kept horses. Compound diets such as this have previously been shown to increase the frequency of chewing cycles and decrease mediolateral excursion. The occurrence of 10 named dental abnormalities present in the dentition of 60 Thoroughbred-type horses was recorded. Half of the population was at grass all year round in New South Wales, Australia. The remainder were stabled for 24 h/day in Gloucestershire, UK. All horses were between 5 and 15 years of age. The same, experienced, equine dental technician examined all horses using a full-mouth speculum and produced a routine dental chart. Stable-kept horses had a significantly higher total occurrence of abnormalities (P < 0.001) than free-living horses. The stable-kept group had a significantly higher prevalence of exaggerated transverse ridging across the occlusal surface of the cheek teeth, focal or ramped overgrowths of the cheek teeth and periodontal disease (P < 0.01 in all cases). All horses in both groups had some occurrence of sharp edges of the buccal and lingual edges of the cheek teeth. The results are in agreement with anecdotal evidence that a fibre-based, grazed diet results in fewer dental abnormalities. However, sharp edges may occur even with what is perceived as a 'natural' diet. [ABSTRACT FROM AUTHOR]

Abstract: The results of 3 years (2005–2007) of observations and mating (5,646 estrous cycles of 3,788 mares bred to 1 of 15 stallions) at one Thoroughbred breeding farm in central Kentucky were analyzed by a multiple logistic regression model using Bayesian statistics to evaluate the relationship between data entries (factors) and pregnancy outcomes. Factors found to be significantly (P < .05) associated with pregnancy outcome included stallion (one stallion had lower OR for pregnancy higher odds ratio [OR] for pregnancy, and one had, than other stallions), date of mating (OR for pregnancy declined slightly in May – July), mare age (OR for pregnancy were higher for mares <13 years old, and lower for mares >18 years old), mare beginning status (foaling mares had a higher OR for pregnancy), mating on foal heat (lowered OR for pregnancy), mating of the day for the stallion (OR for pregnancy was 4.16 times lower for fifth compared with first mating of day), reinforcement breeding (increased OR for pregnancy), dismount semen neutrophil score (lowered OR for pregnancy when neutrophils were present in dismount semen samples), and tranquilization before breeding (lowered OR for pregnancy in foaling and barren mares). The influence of dismount sample sperm motility scores on OR for pregnancy was weak, so motility scores were not included in the final logistic regression model. The majority of variation in pregnancy outcome was because of mare factors, with only approximately one-third of the variation in fertility explained by stallion. [Copyright &y& Elsevier]

A study was carried out on 100 horses of Thoroughbred (20), Arabian (20) and Akhal-Teke breeds (60) to determine chestnut dimensions and its relation with age of horse and length of respective limbs. Results showed that the means of forelimb chestnut length (2.604±0.601 cm) and width (1.617±0.41 cm) were significantly more (P<0.01) than hind limb chestnut length (2.202±0.627 cm) and width (1.313±0.388 cm). In Thoroughbreds hind limb length was significantly more than that of Arabian and Akhal-Teke breeds and in Arabian breeds it was more than Akhal-Teke (P<0.05). The length of fore limb in Akhal-Teke breed was significantly less than that of Arabian breed (P<0.014). The length of chestnut increased (r= +0.829, Pvalue= 0.021) and and width decrease (r= -0.724, Pvalue= 0.043) with aging in Arabian and Thoroughbred horses, the chestnut dimensions varied with the age, body weight and length of respective limbs in horses. [ABSTRACT FROM AUTHOR]

Abstract: In Thoroughbred breeding, it is sometimes necessary to tranquilize a maiden mare to accomplish safe breeding by natural service. To determine whether tranquilization adversely affected fertility of maiden mares, pregnancy rates achieved in 792 matings of 531 maiden Thoroughbred mares were evaluated. One hundred sixty-three matings were accomplished after administration of a tranquilizer cocktail (20 mg acepromazine, 100 mg xylazine, and 10 mg butorphanol tartrate, injected intravenously), whereas 598 matings were accomplished without tranquilization. Pregnancy rate/cycle did not differ between maiden mares tranquilized before (64%; 105/163) and mares not tranquilized before mating (69%; 434/629) (χ2 = 1.048; P > .05). We concluded that tranquilization of maiden Thoroughbred mares immediately before mating did not adversely affect fertility. [Copyright &y& Elsevier]

A survey of 72 thoroughbred trainers in several regions of NSW was conducted to better define current grain feeding practices, and the risks involved with grain feeding in the Australian thoroughbred racing industry. Results from the survey indicate that horses in the industry are currently being fed an average of 7.3 ± 0.23 kg of grain concentrate per day, with oats, commercial pre-mixed diets and corn most commonly used. The feeding of extruded, micronised and steam flaked grains was uncommon. The results of grain and faecal sample analyses conducted during the survey indicate that incomplete starch digestion in the equine small intestine and subsequent hindgut starch fermentation and low hindgut pH are common. These observations quantify the adverse impact of current grain feeding practices on faecal measures of gut health and demonstrate that when selecting grains for use in the thoroughbred racehorse, greater emphasis should be placed on the starch digestibility characteristics of grains. [ABSTRACT FROM AUTHOR]

Abstract: Insulin resistance has been detected in obese Morgan horses and it has been suggested that horses of this breed are predisposed to this condition. The objective of this study was to determine whether blood lipid, glucose, and insulin concentrations differed between Morgan horses and Thoroughbreds housed at the same facility. Fourteen Morgan horses (five mares, nine geldings) ranging in age from 4 to 14 years were compared with 21 Thoroughbreds (11 mares, 10 geldings; age range 7–20 years) from the same herd. A single blood sample was collected from each horse after grain was withheld overnight. Variables were compared between breed groups and breed-specific reference ranges were calculated. Triglyceride, cholesterol, nonesterified fatty acid, glucose, and insulin concentrations did not differ between breeds of horse in this study. This may be because horses included in this study did not suffer from obesity and were regularly exercised. [Copyright &y& Elsevier]

Single nucleotide polymorphisms (SNPs) in the p53 gene have been studied extensively in humans. The aims of this study were to determine the frequency of the Arg/Pro SNP in p53 in Thoroughbred mares on one stud in Brazil and to correlate p53 genotypes with reproductive performance. SNPs were detected by PCR-restriction fragment length polymorphism in blood samples from 105 horses and confirmed by sequencing. The allele frequency in Thoroughbred mares at codon 72 in exon 4 was 73.3% Arg/Pro, 17.1% Arg/Arg and 9.6% Pro/Pro. The presence of Arg/Pro was significantly associated with abortion (P = 0.02), while Pro/Pro mares had a lower probability of abortion (P < 0.05). Using a logistic regression model, the dominance effect was significant (P = 0.044; odds ratio 7.94) for abortion and additive effects were not significant (P= 0.26). p53 may play a role in equine reproduction. [ABSTRACT FROM AUTHOR]