Standardbred Racehorses Research Articles

A cross-sectional study on performance evaluation in Italian standardbred horses’ real-time PCR-positive for Theileria equi

BackgroundInflammatory myopathy and perivasculitis have been recently described in horses with chronic equine piroplasmosis (EP). These alterations may be linked to poor performances. The aims of this study were to evaluate the prevalence for EP in clinically healthy Italian Standardbred (IS) racehorses and to compare laboratory parameters and performance metrics between positive and negative horses. Real-time PCR was applied for the detection of T. equi and B. caballi positivity. Haematology parameters, blood chemistry results, subjective muscle mass scores, and performance metrics were compared between PCR-positive and -negative horses.ResultsThis cross-sectional study included 120 well-trained IS racehorses and was performed over a two-years period. The prevalence of T. equi was 36.3%, whereas all samples were negative for B. caballi. Red blood cells count, haemoglobin concentration, aspartate aminotransferase, alkaline phosphatase, and gamma-glutamyl transferase activities were significantly higher in PCR-positive horses, whereas blood urea nitrogen, globulin concentration and globulin-to-albumin ratio were significantly lower in PCR-positive horses compared to PCR-negative ones. Nonetheless, all values fell within the physiological range. The best racing time, which was selected as the most representative of the performance metrics at the principal component analysis, was not affected by PCR positivity, the muscle mass score or the training yard. The best racing time was significantly better in horses with a mild or no signs of muscular atrophy, within the PCR-positive group. The muscle mass score was associated with the training yard in PCR-negative horses.ConclusionsPrevalence of T. equi was high in IS racehorses in southern Italy. The absence of obvious changes in haematological and biochemical parameters, as well as performance metrics in positive horses, highlights the need for specific diagnostic tests to identify chronically infected horses.

Long-Term Training Increases Atrial Fibrillation Sustainability in Standardbred Racehorses.

Atrial fibrillation (AF) is more prevalent in athletes, and currently, the mechanisms are not fully understood. Atrial fibrillation inducibility and stability was investigated in trained and untrained Standardbred racehorses. The horses underwent echocardiography for evaluation of atrial size. High-density mapping during AF was performed, and the presence of structural remodeling, as well as the expression of inflammatory and pro-inflammatory markers in the atria, was studied. Atrial fibrillation sustained significantly longer after tachypacing in the trained horses, whereas no difference in AF inducibility was found. The untrained horses displayed a significant difference in the AF complexity when comparing right and left atria, whereas such difference was not observed in the trained animals. No evidence of increased structural remodeling or inflammation could be identified. Left atrial dimensions were not significantly increased. The increased AF sustainability in trained horses was not related to fibrosis or inflammation as seen in other animal exercise models.

Variation in palmaromedial articulations of carpometacarpal joints in Thoroughbred and Standardbred racehorses

Background: Carpal conformation is an important factor in relation to the joint soundness. The equine carpometacarpal joint was reported to have variations in its three palmaromedial articulations. Lacking one or more of these articulations has not been radiographically evaluated in Thoroughbred (TB) and Standardbred (SB) racehorses. Aim: The study aimed to identify the prevalence of the variation in the palmaromedial articulation of the carpometacarpal joint (PM-CMCJ) in TB and SB horses. Additionally, to detect the probability of having each of the three articulations within and between the breeds. Finally, to establish an anatomical description for the different patterns of the articulations in these horses. Methods: 313 dorsopalmar radiographs from 174 horses (117 TB and 57 SB) were used. Three articulations at PM-CMCJ were evaluated based on their presence or absence: the articulations between the second and third carpal bones (C2-C3), the second carpal-second metacarpal (C2-Mc2) and the second and third metacarpal (Mc2-Mc3) bones. Probability of each articulation was determined in the breeds. Depending on the presence/absence of one or more of these articulations in each horse, each group of horses that had the same patterns of the articulation was gathered into one category. Results: Prevalence of variation in articulations of PM-CMCJ was identified in about 28% of the horses. SB showed a higher variation than TB throughout the comparisons. C2-C3 articulation was significantly the most common articulation, especially in TB (98%). The most common pattern of articulations (73%) was found in Category I, which had the three articulations whereas 3 horses that grouped in Category VI had no palmaromedial articulations. Conclusion: The variations in the articulations of PM-CMCJ in TB and SB racehorse might show a breed association. C2-C3 articulation was considerably the most frequent feature and Category I was the common pattern of articulations in PM-CMCJ. Potential clinical effects of the varied patterns of the articulations require investigation.

Enriched Pathways of Calcium Regulation, Cellular/Oxidative Stress, Inflammation, and Cell Proliferation Characterize Gluteal Muscle of Standardbred Horses between Episodes of Recurrent Exertional Rhabdomyolysis.

Certain Standardbred racehorses develop recurrent exertional rhabdomyolysis (RER-STD) for unknown reasons. We compared gluteal muscle histopathology and gene/protein expression between Standardbreds with a history of, but not currently experiencing rhabdomyolysis (N = 9), and race-trained controls (N = 7). Eight RER-STD had a few mature fibers with small internalized myonuclei, one out of nine had histologic evidence of regeneration and zero out of nine degeneration. However, RER-STD versus controls had 791/13,531 differentially expressed genes (DEG). The top three gene ontology (GO) enriched pathways for upregulated DEG (N = 433) were inflammation/immune response (62 GO terms), cell proliferation (31 GO terms), and hypoxia/oxidative stress (31 GO terms). Calcium ion regulation (39 GO terms), purine nucleotide metabolism (32 GO terms), and electron transport (29 GO terms) were the top three enriched GO pathways for down-regulated DEG (N = 305). DEG regulated RYR1 and sarcoplasmic reticulum calcium stores. Differentially expressed proteins (DEP ↑N = 50, ↓N = 12) involved the sarcomere (24% of DEP), electron transport (23%), metabolism (20%), inflammation (6%), cell/oxidative stress (7%), and other (17%). DEP included ↑superoxide dismutase, ↑catalase, and DEP/DEG included several cysteine-based antioxidants. In conclusion, gluteal muscle of RER-susceptible Standardbreds is characterized by perturbation of pathways for calcium regulation, cellular/oxidative stress, inflammation, and cellular regeneration weeks after an episode of rhabdomyolysis that could represent therapeutic targets.

Electrocardiographic characteristics of trained and untrained standardbred racehorses.

BackgroundLong‐term exercise induces cardiac remodeling that potentially influences the electrical properties of the heart.Hypothesis/objectivesWe assessed whether training alters cardiac conduction in Standardbred racehorses.AnimalsTwo hundred one trained and 52 untrained Standardbred horses.MethodsCross‐sectional study. Resting ECG recordings were analyzed to assess heart rate (HR) along with standard ECG parameters and for identification of atrial and ventricular arrhythmias. An electrophysiological study was performed in 13 horses assessing the effect of training on sinoatrial (SA) and atrioventricular (AV) nodal function by sinus node recovery time (SNRT) and His signal recordings. Age and sex adjustments were implemented in multiple and logistic regression models for comparison.ResultsResting HR in beats per minute (bpm) was lower in trained vs untrained horses (mean, 30.8 ± 2.6 bpm vs 32.9 ± 4.2 bpm; P = .001). Trained horses more often displayed second‐degree atrioventricular block (2AVB; odds ratio, 2.59; P = .04). No difference in SNRT was found between groups (n = 13). Mean P‐A, A‐H, and H‐V intervals were 71 ± 20, 209 ± 41, and 134 ± 41 ms, respectively (n = 7). We did not detect a training effect on AV‐nodal conduction intervals. His signals were present in 1 horse during 2AVB with varying H‐V interval preceding a blocked beat.Conclusions and Clinical ImportanceWe identified decreased HR and increased frequency of 2AVB in trained horses. In 5 of 7 horses, His signal recordings had variable H‐V intervals within each individual horse, providing novel insight into AV conduction in horses.

Effects of Standardized Exercise Tests on Plasma Thyroid Hormones’ Kinetics in Standardbred Racehorses

This study examined how a standard exercise test (SET) affected (1) thyroid hormones (THs) of horses and (2) the relationship between the VLa4 of horses and TH responses to the exercise in trained Standardbred racehorses (VLa4 is the velocity run at defined conditions at which a blood lactate concentration of 4 mmol/L is determined). Twelve trained Standardbred racehorses (six stallions and six mares) performed SETs until the horses’ blood lactate concentration was at or above 4 mmol/L. The horses were divided into three age groups (2, 3, and 4 years old); each group consists of 4 horses respectively (two male and two female), to evaluate the effects of age and sex on hormonal responses to SET. During each SET, blood samples were taken at rest and after each interval and at the end of SET. Blood was analysed for total and free triiodothyronine (T3, fT3) as well as total and free thyroxine (T4, fT4). The statistical model included three fixed factors (SET, sex and age) and their main interactions. ANOVA analysis revealed that T3 and fT3 were significantly influenced by SETs. Plasma T3 and fT3 concentrations were higher in 4-year-old horses compared to the other age groups. All plasma THs concentrations were higher in mares than in stallions. Correlations revealed that a higher VLa4 was negatively related to all THs responses in 2-year-old Standardbred mares only. The SET used to determine VLa4 increased selected THs (T3, fT3); these increases were inversely related to VLa4 and affected by age and sex of the horses. The correlation of VLa4 with thyroid exercise’ response might provide some additional information for performance evaluation of Standardbred racehorses, especially for evaluating training adaptation, according to sex, and age. Further studies are necessary to provide support on the value of measuring THs in Standardbred racehorses of different sex and age.

Innovative Blood Antioxidant Test in Standardbred Trotter Horses.

In athletic horses, prolonged and intense training gives rise to an imbalance between the production of free radicals and antioxidant molecules, leading to oxidative stress. Considering the relation between exercise and oxidative stress in horses, the present work aims to validate the Kit Radicaux Libres (KRL) test as a tool to verify the influence of taming, training and racing on the total blood antioxidant activity and some haematochemical parameters. Five Italian Standardbred racehorses (two males and three females, aged 12 ± 1 months) from the same training center were selected and monitored upon arrival and during the following year until the racing season. Blood samples were obtained at different timepoints, corresponding to different steps of training. The data showed that KRL values were higher (p < 0.001) before the beginning of the taming period and at 60 days of taming, compared with the training and racing periods; additionally, the total protein value was affected by the training program, whereas no effects of training on muscle enzymes were detected. These results confirm that exercise plays a role in the production of free radicals and show that the KRL test may represent a valid method to determine oxidative stress in athletic horses.

Intrinsic Electrical Remodeling Underlies Atrioventricular Block in Athletes.

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Prognostic Indicators after Musculoskeletal Injuries in Standardbred Racehorses in Italy

The objective of this study was to report recovery time, retirement rate, racing performance, and presence of compensation pattern after musculoskeletal injuries (MSIs) in Standardbred racehorses (STBRs). This is a retrospective single open-cohort study, enrolling 356 STBRs in training in a single racetrack. Musculoskeletal injury was defined as any training-related injury after which the horse did not train for at least 15 days. The first and second MSIs encountered during the horse’s racing career were considered. Medical records, training logbooks, and racing data were reviewed to determine recovery time, retirement rate, racing performance, and compensation pattern after MSIs. Kaplan–Meier estimators considered the return to activity as primary endpoint. The hazard ratio (HR) for return to activity was determined using Cox proportional hazard models, after classifying horses based on the injury type. A total of 543 MSIs were considered. The 33.6% (95% confidence limits [CL]: 29.5, 37.8) of STBRs suffering from MSI had to be retired as consequence of that. The median recovery time after MSI was 119 days (95% CL: 47, 179). Horses with traumatic osteoarthritis had a greater likelihood of returning to athletic activity compared with horses with stress fractures (HR = 4.8, 95% CL: 3.5, 6.7) and tendon/ligament strains (HR = 4.1, 95% CL: 3.1, 5.4). Increased racing speed was recorded after injuries. The second MSI was more often localized to the contralateral limb compared with the first injury (odds ratio (OR) 6.35, 95% CL: 4.29, 8.51), diagonal (OR 4.59, 95% CL: 3.05, 6.27) and to the same limb (OR 3.17, 95% CL: 2.03, 4.47) than to the ipsilateral limb.

Pre- and post-race serum cardiac troponin T concentrations in Standardbred racehorses

Elevated cardiac troponin T (cTnT) concentrations may provide evidence of myocardial injury but physiological post-exercise release also occurs. Reference intervals are not fully established in horses making interpretation difficult. The aims of this study were to establish an upper reference limit for serum cTnT, compare pre-and post-race serum cTnT concentrations, and to evaluate factors that may influence these in a population of healthy, race-fit Standardbred racehorses. Serum samples were collected pre- (n = 108) and 1–2 h post-racing (n = 101) and analysed using a high sensitivity-cTnT assay. Reference limits with 90% confidence intervals (CI) were calculated by non-parametric methods using the bootstrap method. Effects of sex, age, racing speed, distance, placings and track surface were assessed by fitting generalized linear models with an identity link function and inverse Gaussian distribution.The upper reference limit for serum cTnT concentration was 27.4 ng/L (90% CI 13.1–32.0). The median serum cTnT concentration was significantly higher 1–2 h post-racing compared to pre-racing (P < 0.001). Age and sex did not significantly affect serum cTnT concentrations pre-racing (P = 0.5 and P = 0.11). Cardiac troponin T concentrations were significantly higher post-racing in females (P = 0.018). Racing speed and placings had no effect on serum cTnT concentrations post-race (P = 0.71 and P = 0.66). The study contributed towards establishing an upper reference limit for serum cTnT concentrations in a population of race-fit Standardbreds and evaluated factors that may have influenced the results obtained.

Survey of trainers on the use of swimming exercise for Standardbred racehorses in Australia.

To determine swimming training practices in Australian harness racing horses and potential targets for future research. An online survey of Australian Standardbred trainers and telephone interviews with 20 leading trainers were conducted. Questions relating to swimming facility and protocol, perceived benefits and contraindications were included. Descriptive data analysis was performed. Data were collected from 270 trainers: 250 by online survey (250/1770, response rate 14.1%) and 20 by interview. Of these, 103 trainers (38.1%), including 91 surveyed trainers (91/250, 36.4%) and 12 interviewed trainers (12/20, 60.0%), used swimming exercise. The most popular reasons for swimming were to replace trackwork for horses with limb injuries (79.4%), improve or maintain fitness (62.7%) and provide mental stimulation through variety in training (40.0%). Free swimming (78.4%) was more common than tethered, but the frequency and duration for horses in full training varied widely between trainers, with a median of four swim sessions per horse each week (range 0.5-12) for a median of 7 min (range 1.5-30 min) per session, mostly as a continuous swim, but sometimes as intervals. The main reasons given by those not swimming horses were lack of an adequate facility (60.5%) and lack of perceived benefit (16.2%). Reasons for not swimming individual horses varied widely. Trainer opinions and protocols varied widely with respect to swimming exercise for Standardbred race horses. The role of swimming exercise requires further study so that evidence-based recommendations can be made.

Radiographic Comparison of Carpal Morphometry in Thoroughbred and Standardbred Race horses

Carpal conformation is thought to contribute to the frequency of carpal pathology so non-invasive measurement of carpal morphometry would be useful to identify joints at risk. However, there are scant radiographic morphometrical details for the carpals of Thoroughbred (TB) and Standardbred (SB) racehorses even though these breeds differ in the incidence of carpal damage. This study aimed to identify morphometrical similarities and differences in carpal conformation in TB and SB. Thirty carpal dorsopalmar radiographs (DP) were collected from 15 TB and 15 SB. All DP radiographs were at zero degrees or within the acceptable range of rotation. Twelve carpal radiographic parameters were selected and measured on each radiograph. Statistical analysis found significant differences in four carpal parameters. These parameters revealed that the middle carpal joint in SB was significantly more angled distomedially whereas the radial distal metaphysis showed a greater distolateral inclination in TB. The radiocarpal and the carpometacarpal articulations exhibited common features in the two groups of horses. These carpal traits in TB and SB highlight their potential association with loading distribution and pathology. Measuring carpi from untrained and injured horses is necessary to establish breed specific features for the ideal carpal conformation in each of these breeds.

Post‐exercise cardiac troponin I release and clearance in normal Standardbred racehorses

SummaryBackgroundThere are currently no studies detailing cardiac troponin I (cTnI) release in normal horses post‐exercise using an analytically validated assay. These data are essential for selecting appropriate sampling times in equine athletes with suspected myocardial injury.ObjectiveTo plot the magnitude and time course of cTnI release after maximal effort, using validated cTnI assays.Study designDescriptive longitudinal study.MethodsFive clinically normal Standardbred racehorses in race training were included in the study. Horses were exercised in harness at near‐race intensity. Blood samples were taken immediately pre‐ and post‐exercise and then hourly for 24 h. Samples were analysed using the validated high‐sensitivity cTnI assay and a contemporary sensitivity cTnI assay.ResultsMean resting cTnI was 1.33 ± 0.6 s.d. ng/L (range, 0.82–2.33 ng/L) using assay A. All horses were below the detection limit at rest using assay B. Peak elevation occurred 2–6 h post‐exercise with both assays (mean, 4.6 ± 1.7 and 4.0 ± 2 h, respectively). Mean peak increase in cTnI was 11.96 ± 9.41 ng/L (range, 1.72–23.76 ng/L) using assay A. Peak concentrations were detectable in three of the horses using assay B and were between 0.039 and 0.051 μg/L (mean: 0.043 ± 0.006 μg/L). All horses returned to baseline within 24 h.Main limitationsA small (n = 5) convenience sample was used as random sampling was not logistically possible.ConclusionsAll horses experienced an increase in cTnI post‐exercise, with peak occurring 2–6 h post‐exercise. Cardiac troponin I elevation was detected earlier using the high‐sensitivity assay, which may convey a diagnostic advantage. Targeted studies are needed to determine the significance of these increases.

The effects of acute strenuous exercise on the faecal microbiota in Standardbred racehorses

While exercise has been found to change the faecal microbiome (FM) in laboratory animals exposed over weeks, no studies have identified immediate changes in the FM associated with short spans of intense exercise, ~5 min. The purpose of this study was to test the hypothesis that acute intense exercise would alter the FM in horses. Each horse performed two rounds of testing undergoing both a graded exercise test (GXT) and a parallel standing control (SC) trial before (GXT1 and SC1) and after (GXT2 and SC2) 12 weeks of exercise training. Rectal faecal samples were taken 24 h before and after testing. Bacterial community analysis was done by sequencing the 16s rRNA (V3-V4) region via Illumina Miseq. The relative abundance of the genus Clostridium significantly decreased in SC1 (P&lt;0.05), with a concurrent decrease in the Shannon diversity index at the species level (P&lt;0.05). At both the genus and species levels the principle coordinate analysis (PCoA) showed significant separation when the samples collected before SC1 were compared to those collected after SC1 (P&lt;0.05). Interestingly, we found that Fusicatenibacter saccharivorans, a bacteria found to be decreased in ulcerative colitis patients, and Treponema zioleckii, a bacteria found to degrade fructan in sheep rumen, were significantly decreased when the samples collected before SC1 were compared to those collected after SC1 (P&lt;0.05). None of the changes observed in SC1 happened in SC2 (P&gt;0.05). Our results indicate that very intense acute exercise does not alter the faecal microbiome of the Standardbred race horse and that 12 weeks of exercise training does not alter that response.

Influence of bronchoalveolar lavage volume on cytological profiles and subsequent diagnosis of inflammatory airway disease in horses

The aim of the study was to determine whether instillation of either 250 mL or 500 mL of saline for bronchoalveolar lavage (BAL) would influence cytological confirmation of inflammatory airway disease (IAD). Thirty client-owned Standardbred racehorses were sampled via endoscopy with 250 mL of saline in one lung and 500 mL in the contralateral lung. The procedure was repeated 72 h later, reversing the volume per lung. The proportions of BAL fluid (BALF) recovered were significantly higher and neutrophil percentages significantly lower with the larger volume. A poor agreement was found between methodologies in terms of final diagnosis, when based on proportions of neutrophils (>10% from at least one lung). Within the recommended range (250–500 mL), the instilled volume significantly influenced cytological profiles. Establishing specific BALF reference values is warranted.

Post-exercise cardiac troponin I release and clearance in normal Standardbred racehorses.

There are currently no studies detailing cardiac troponin I (cTnI) release in normal horses post-exercise using an analytically validated assay. These data are essential for selecting appropriate sampling times in equine athletes with suspected myocardial injury. To plot the magnitude and time course of cTnI release after maximal effort, using validated cTnI assays. Descriptive longitudinal study. Five clinically normal Standardbred racehorses in race training were included in the study. Horses were exercised in harness at near-race intensity. Blood samples were taken immediately pre- and post-exercise and then hourly for 24h. Samples were analysed using the validated high-sensitivity cTnI assay and a contemporary sensitivity cTnI assay. Mean resting cTnI was 1.33±0.6s.d.ng/L (range, 0.82-2.33ng/L) using assay A. All horses were below the detection limit at rest using assay B. Peak elevation occurred 2-6h post-exercise with both assays (mean, 4.6±1.7 and 4.0±2h, respectively). Mean peak increase in cTnI was 11.96±9.41ng/L (range, 1.72-23.76ng/L) using assay A. Peak concentrations were detectable in three of the horses using assay B and were between 0.039 and 0.051μg/L (mean: 0.043±0.006μg/L). All horses returned to baseline within 24h. A small (n=5) convenience sample was used as random sampling was not logistically possible. All horses experienced an increase in cTnI post-exercise, with peak occurring 2-6h post-exercise. Cardiac troponin I elevation was detected earlier using the high-sensitivity assay, which may convey a diagnostic advantage. Targeted studies are needed to determine the significance of these increases.

Relationships between equine airway reactivity measured byflowmetric plethysmography and specific indicators of airway inflammation in horses with suspected inflammatory airway disease.

Agreement between airway reactivity measured by flowmetric plethysmography and histamine bronchoprovocation, and lower airway inflammation measured by bronchoalveolar lavage (BAL) cytology, has not been studied in horses with suspected inflammatory airway disease (IAD). We tested the hypothesis that airway reactivity is associated with BAL cytology in horses presenting for unexplained poor performance and/or chronic cough. Prospective clinical study. Forty-five horses, predominantly young Standardbred racehorses, presenting for unexplained poor performance or chronic cough, underwent endoscopic evaluation, tracheal wash, flowmetric plethysmography with histamine bronchoprovocation and BAL. Histamine response was measured by calculating PC35, the concentration of nebulised histamine eliciting an increase in Δflow of 35%. In this population, there was no significant correlation between histamine response and cell populations in BAL cytology. When airway hyperreactivity (AHR) was defined as ≥35% increase in Δflow at a histamine concentration of <6mg/ml, 24 of the 45 horses (53%) were determined to have AHR. Thirty-three (73%) had either abnormal BAL cytology or AHR, and were diagnosed with IAD on this basis. Of horses diagnosed with IAD, 9 (27%) had an abnormal BAL, 11 (33%) had AHR and 13 (39%) had both. Airway reactivity and BAL cytology did not show concordance in this population of horses presenting for unexplained poor performance and/or chronic cough. Failure to include tests of airway reactivity may lead to underdiagnosis of IAD in young Standardbred racehorses that present with clinical signs suggestive of IAD.

Reduced high intensity training distance had no effect on VLa4 but attenuated heart rate response in 2-3-year-old Standardbred horses.

BackgroundTraining of Standardbred race horses aims to improve cardiovascular and metabolic functions but studies on the effects of different training strategies from breaking till racing are lacking. Sixteen horses with the goal to race as 3-year-olds were studied from breaking (1-year-olds) to December as 3-year-olds. Horses were allocated to either a control (C) or reduced (R) training program from 2 years of age. The aim was to evaluate the effect of reducing the distance of high intensity exercise by 30% with respect to velocity at lactate concentration 4 mmol/l (VLa4), blood lactate and cardiovascular response. All training sessions were documented and heart rate (HR) was recorded. A standardized exercise test of 1,600 m was performed 10 times and a VLa4 test was performed five times.ResultsC horses initially exercised for a longer time with a HR >180 beats per minute compared to R horses (P < 0.05) but after 6–9 months, time with HR >180 bpm decreased in C and were similar in the two groups (P > 0.05). Over the 2-year period, recovery HR after the 1,600 m-test decreased in both groups but was within 2 months lower in C than in R (P < 0.05). C horses also had lower resting HR as 3-year-olds (P < 0.01) than R horses. In C, post exercise hematocrit was higher than in R (P < 0.05). There was a tendency (P < 0.1) towards a larger aortic diameter in C as 3-year-olds (C: 1.75 ± 0.05, R: 1.70 ± 0.05 cm/100 kg BW). Left ventricle diameter and blood volume (in December as 2-year-olds) did not differ between groups. There were no differences between groups in post exercise blood lactate concentration or in VLa4. Both groups were equally successful in reaching the goal of participation in races.ConclusionsHorses subjected to a reduced distance of high intensity training from the age of 2 showed an attenuated heart rate response, but were able to maintain the same VLa4 and race participation as horses subjected to longer training distances.

Cytokine concentrations in bronchoalveolar lavage fluid from horses with neutrophilic inflammatory airway disease.

BackgroundMultiple cytological patterns occur in bronchoalveolar lavage fluid (BALF) of horses with inflammatory airway disease (IAD). Only few data on BALF cytokine profiles are available for horses with IAD, and are limited to mRNA expression.Hypothesis/ObjectiveCytological profiles of IAD are associated with different BALF immunological pathways. To investigate BALF cytokine concentrations in a large number of horses with neutrophilic IAD.AnimalsOne hundred and thirty‐eight client‐owned Standardbred racehorses in active training.MethodsProspective observational study. BALF samples were obtained from left and right lungs. Interleukin (IL)‐4, interferon (IFN)‐γ, and tumor necrosis factor (TNF)‐α concentrations were determined by ELISA.ResultsFourteen horses had normal BALF cytological profiles and 56 exhibited evidence of bilateral neutrophilic IAD. Twenty‐four horses showed BALF with, respectively, IAD‐ and CTL consistent cytology and were excluded; as were 44 horses because of evidence of pulmonary hemorrhage. TNF‐α (56 ± 115 pg/mL; P = .034) and IFN‐γ concentrations (104 ± 247 pg/mL; P = .044) were significantly higher for IAD horses, compared with controls (respectively 19 ± 41 and 80 ± 116 pg/mL). Horses with ‘neutrophil’ subtype had significantly higher IFN‐γ concentrations (110 ± 154 pg/mL), than ‘neutrophil/metachromatic’ (56 ± 54 pg/mL; P = .028) and ‘neutrophil/metachromatic/eosinophil’ subtypes (44 ± 23 pg/mL; P = .012).Conclusions and Clinical ImportanceCytokine concentrations in BALF suggested that neutrophilic IAD is associated with activation of the innate immune system and a possible T‐helper (Th)‐1 polarized response. This study also suggested that immunological pathways vary according to cytological IAD subtypes.

Short- and long-term racing performance of Standardbred pacers and trotters after early surgical intervention for tarsal osteochondrosis.

Osteochondrosis (OC) is commonly diagnosed in young Standardbred racehorses but its effect on performance when surgically treated at a young age is still incompletely understood. This is especially true for Standardbred pacers, which are underrepresented in the existing literature. To characterise the short- (2-year-old) and long-term (through 5-year-old) racing performance in Standardbred pacers and trotters after early surgical intervention (<17 months of age) for tarsal OC. Retrospective clinical study. The study population consisted of related, age-matched Standardbred racehorses (n = 278; 151 pacers, 127 trotters) with (n = 133) or without (n = 145) one or more tarsal OC lesions. All OC-affected horses were treated surgically prior to being sold as yearlings. Data obtained from publicly available race records for each horse included starts, wins, finishes in the top 3 (win, place or show), earnings and fastest time. Comparisons between OC-affected and unaffected horses were made for the entire population and within gaits. A smaller related population (n = 94) had these performance measures evaluated for their 2-5-year-old racing seasons. Osteochondrosis status was associated with few performance measures. Trotters were at higher risk for lesions of the medial malleolus but lower risk for lesions of the distal intermediate ridge of the tibia than were pacers. Horses with bilateral OC lesions and lateral trochlear ridge (LTR) lesions started fewer races at 2 years of age than those with unilateral lesions or without LTR lesions. Osteochondrosis seemed to have minimal effect on racing performance in this cohort, although horses with bilateral and LTR lesions started fewer races at 2 years. There was evidence for different distribution of OC lesions among pacers and trotters, which should be explored further. Standardbreds undergoing early removal of tarsal OC lesions can be expected to perform equivalently to their unaffected counterparts.