Inheritance of racing performance of trotter horses: An overview

Harness racing is a form of horseracing in which the horses race in a specified gait (trot or pace). In contrast to the Thoroughbred, the trotter is not an international breed. In this type, the horses are raced with trotting or pacing gait. Breeds specialized for racing at trot or pace are indigenous to many countries. Separate breeds of light harness horses, generally designated as trotters have evolved for racing purposes in several countries. The important horse breeds used for harness racing in different parts of the world are the Standardbred, French Trotter, Swedish Trotter, Orlov Trotter, Russian Trotter, Finnhorse, Icelandic Toelter, Dole horse and North-Swedish cold-blooded horses. The trotter ranks worldwide second to the Thoroughbred in popularity as a racehorse. Racing performance in trotters, in contrast to Thoroughbred is characterized by qualifying tests before entering the races, inclusion of more than one breed in international races only and greater duration of racing career. An intensive selection of stallions on the basis of phenotypic racing performance has been practised in many trotter populations for quite a long time. Unlike Thoroughbreds, improvements have been observed in different trotter populations and this is attributed to both genetic and environmental changes. Environmental changes include enhanced training methods, as well as improved tracks, harness and sulkies. As a result of selection, racing time of trotters has been reduced over the years. The estimated annual genetic progress in racing performance traits of Swedish Standardbred horses corresponds to 5% of the phenotypic standard deviation, 3.6% in French Trotters and 5% in Dutch Trotters. According to the recent selection for speed in trot, this trait remains heritable and genetic improvement is observed in most countries. Correlations between earnings and times are negative and high, and hence favourable. As a result, selection based on times and earnings are quite effective. A multiple trait approach avoids potential biases of one particular measure, even if the objective of all traits is much the same. Since racing performance may be evaluated in both males and females and repeated observations can be obtained on the same animal, mass selection based on performance tests would be the selection procedure of choice. In the future, interest in the possible use of marker-assisted selection (MAS) for enhanced genetic improvement in horses is likely to increase. MAS is likely to be a valuable complement to selection of horses based on estimated breeding values (EBVs) obtained by the Best Linear Unbiased Prediction (BLUP) method, rather than as a replacement for EBVs.     

Multivariate genetic analysis to account for preselection and disqualified races in the genetic evaluation of racing performances in German trotters

Abstract

The genetic associations between racing performance and preselection of horses considered as the binary trait racing status (trotters without or with at least one racing performance in life were classified as 0 and 1, respectively) as well as disqualified races (disqualified and non-disqualified trotters were classified as 1 and 0, respectively) were analysed in German trotters. Variance components for racing performance traits square root of rank at finish, racing time per km, and log of earnings with racing status were estimated based on an animal model using REML. Heritabilities of racing status, racing time and rank at finish were 0.30, 0.21, and 0.06, respectively. The genetic correlations between racing status and racing time or rank at finish were ?0.74 and ?0.32, indicating that horses started at least once showed a higher genetic potential in racing time or finishing ability than never started horses. This showed the high preselection of German trotters especially based on racing time. To account for this preselection, it was recommended for additional use of racing status in the German evaluation system. Breeding values of the three racing performance traits were estimated by two distinct models, in- or excluding racing status and compared by using three criteria. Racing time per km showed the highest correlation (r=0.98) between breeding values evaluated by these two distinct models. Therefore, incorrect selection rate of horses using breeding values from the model without racing status, was lowest for racing time per km (9.7%). Selection response increased about 1% for this trait after including racing status in the model. For the estimation of rank at finish, inclusion of racing status in the multiple trait model was much more important as indicated by a low correlation between breeding values (r=0.29) and high percentage of incorrectly selected stallions (97.5%). The trait disqualified races was first analysed using an univariate threshold model. Heritability of this trait was low (h ²=0.12) and repeatability (r=0.43) showed a moderate magnitude. Using a linear multiple trait animal model, disqualified races showed a low heritability (h ²=0.05) and a moderate favourable genetic correlation (r _g=0.43) with racing time per km. Consequently, selection on racing time per km is expected to improve indirectly the reliability of racing performance. Combined selection of reduction in disqualified races and racing time may even further improve the reliability of racing trotters.     

Genetic predictions of racing performance in quarter horses

Research on the racing performance of quarter horses has been used to develop genetic prediction summaries on all horses with at least one start on record at the American Quarter Horse Association. In the 1987 summary, records from a total of 212,065 horses were used to give genetic predictions on stallions, mares, geldings, fillies, and colts. A reduced animal model was used that incorporated the repeated records of individuals. The individual race was the contemporary group after the data were adjusted for distance, sex, and age. Estimates of heritability of .24 and repeatability of .32 suggest that increased racing performance can be achieved if the predictions are used by breeders. Continued research in variance component estimation includes the genetic covariances among the several distances, maternal influence, and genetic parameters for racing longevity.     

The use of a random regression model to account for change in racing speed of German trotters with increasing age

In a genetic analysis of German trotters, the performance trait racing time per km was analysed by using a random regression model on six different age classes (2‐, 3‐, 4‐, 5‐ and 6‐year‐old and older trotters; the age class of 3‐year‐old trotters was additionally divided by birth months of horses into two seasons). The best‐fitting random regression model for the trait racing time per km on six age classes included as fixed effects sex, race track, condition of race track (fitted as second‐order polynomial on age), distance of race and each driver (fitted as first‐order polynomial on age) as well as the year‐season (fitted independent of age). The random additive genetic and permanent environmental effects were fitted as second‐order polynomials on age. Data consisted of 138 620 performance observations from 2373 trotters and the pedigree data contained 9952 horses from a four‐generation pedigree. Heritabilities for racing time per km increased from 0.01 to 0.18 at age classes from 2‐ to 4‐year‐old trotters, then slightly decreased for 5 year and substantially decreased for 6‐year‐old horses. Genetic correlations of racing time per km among the six age classes were very high (r_g = 0.82–0.99). Heritability was h² = 0.13 when using a repeatability animal model for racing time per km considering the six age classes as fixed effect. Breeding values using repeatability analysis over all and within age classes resulted in slightly different ranking of trotters than those using random regression analysis. When using random regression analysis almost no reranking of trotters over time took place. Generally, the analyses showed that using a random regression model improved the accuracy of selection of trotters over age classes.     

Comparison of two different statistical models considering individual races or racetracks for evaluation of German trotters

Two different statistical models considering racetrack or individual race as fixed effect were compared, regarding genetic parameters and by using cross validation. Data for variance component estimation consisted of 48,942 performance observations from 4249 trotters. Variance components for the traits square root of rank at finish, racing time per km, and log of earnings per race were estimated by REML using two multiple trait animal models involving different racetracks or individual races. When including each individual race instead of racetracks in the statistical model, heritabilities increased from 0.05 to 0.07, 0.19 to 0.23, and 0.08 to 0.09 for square root of rank at finish, racing time per km, and log of earnings per race, respectively. Genetic and phenotypic correlations among traits increased also after consideration of individual races. Square root of rank at finish, as well as racing time per km and log of earnings per race, was highly genetically correlated with −0.99 and −0.88. The two statistical models were compared on the basis of their predictive ability by using cross validation. Data for these analyses consisted of 706,082 observations from 21,363 trotters. Randomly eliminated performance observations were predicted by cumulation of fixed and random effects obtained from estimation of breeding values for both models. Estimates for racing time showed lower bias and mean square error (MSE) when considering individual races instead of racetracks. Also, the correlation between predicted and true phenotypic value increased from 0.85 to 0.92. Estimates for square root of rank at finish were unbiased, but with a higher MSE when considering individual race effect. A similar high bias and MSE with both models were obtained for log of earnings. In order to avoid bias in estimation of genetic parameters and breeding values for racing time and square root of rank at finish, inclusion of each individual race in the statistical model was recommended.     

Genetic parameters for racing records in trotters using linear and generalized linear models

Heritability and repeatability and genetic and phenotypic correlations were estimated for trotting race records with linear and generalized linear models using 510,519 records on 17,792 Finnhorses and 513,161 records on 25,536 Standardbred trotters. Heritability and repeatability were estimated for single racing time and earnings traits with linear models, and logarithmic scale was used for racing time and fourth-root scale for earnings to correct for nonnormality. Generalized linear models with a gamma distribution were applied for single racing time and with a multinomial distribution for single earnings traits. In addition, genetic parameters for annual earnings were estimated with linear models on the observed and fourth-root scales. Racing success traits of single placings, winnings, breaking stride, and disqualifications were analyzed using generalized linear models with a binomial distribution. Estimates of heritability were greatest for racing time, which ranged from 0.32 to 0.34. Estimates of heritability were low for single earnings with all distributions, ranging from 0.01 to 0.09. Annual earnings were closer to normal distribution than single earnings. Heritability estimates were moderate for annual earnings on the fourth-root scale, 0.19 for Finnhorses and 0.27 for Standardbred trotters. Heritability estimates for binomial racing success variables ranged from 0.04 to 0.12, being greatest for winnings and least for breaking stride. Genetic correlations among racing traits were high, whereas phenotypic correlations were mainly low to moderate, except correlations between racing time and earnings were high. On the basis of a moderate heritability and moderate to high repeatability for racing time and annual earnings, selection of horses for these traits is effective when based on a few repeated records. Because of high genetic correlations, direct selection for racing time and annual earnings would also result in good genetic response in racing success.     

Validation of alternative models in genetic evaluation of racing performance in North Swedish and Norwegian cold-blooded trotters

There have been several approaches to the estimation of breeding values of performance in trotters, and the objective of this study was to validate different alternatives for genetic evaluation of racing performance in the North Swedish and Norwegian cold-blooded trotters. The current bivariate approach with the traits racing status (RACE) and earnings (EARN) was compared with a threshold-linear animal model and the univariate alternative with the performance trait only. The models were compared based on cross-validation of standardized earnings, using mean-squared errors of prediction (MSEP) and the correlation between the phenotype (Y) and the estimated breeding value (EBV). Despite possible effects of selection, a rather high estimate of heritability of EARN was found in our univariate analysis. The genetic trend estimate for EARN was clearly higher in the bivariate specification than in the univariate model, as a consequence of the considerable size of estimated heritability of RACE and its high correlation with EARN (approximately 0.8). RACE is highly influenced by ancestry rather than the on-farm performance of the horse itself. Consequently, the use of RACE in the genetic analysis may inflate the genetic trend of EARN because of a double counting of pedigree information. Although, because of the higher predictive ability of the bivariate specification, the improved ranking of animals within a year-class and the inability to discriminate between models for genetic trend, we propose to base prediction of breeding values on the current bivariate model.     

Genetic and environmental parameters for racing time at different distances in Brazilian Thoroughbreds

The aim of the present study was to investigate genetic parameters for racing time in Thoroughbred horses racing at distances between 1000 and 1600 m subdivided into 100‐m intervals. The data provided by TURFETOTAL Ltda comprised races that occurred in the Gávea and Cidade Jardim race tracks over a period of 11 years (1992–2002) and consisted of 32 145 races and 238 890 time records. The variance components necessary to obtain the heritability and repeatability estimates of the traits studied were estimated with the MTDFREML program, and animal age at race (3 years old or younger, 4, 5 and older than 5 years), sex (male and female), number of races (1–32 145), and postposition at start (1–11) as fixed effects, and animal and permanent environmental random effects were included in a one‐trait animal model. Males were significantly superior to females at all distances. Excluding the 1100 m distance, animals 4 years of age were significantly faster than the mean of the other ages for all distances analysed. Horses older than 5 years showed a significantly lower performance than the mean of the other ages for all distances analysed, except for the 1100 m. Postpositions one and two did not differ significantly from one another for any of the distances analysed. These two inner positions both together varied from the other positions depending on race length. The components of additive genetic and permanent environmental variance varied in a similar way, tending to decrease with increasing racing distance, and the other temporary environmental variance almost doubled from 1000 to 1600 m. As was the case for the additive genetic and environmental variances, heritability and repeatability estimates tended to decrease with increasing distance, indicating that selection based on racing time will be less successful when the racing distance increases.     

Genetic analysis of racing performance in Irish greyhounds

The aim of this study was to analyse racing performance data in Irish greyhounds with regard to genetic and environmental variation. Estimation of heritabilities for racing time (RT) and ranking, and the prediction of breeding values for all greyhounds in the investigated data were carried out. Data from 42,785 races in Ireland in the years 2000-2003 were available. These results were obtained from 42,880 greyhounds on 20 race tracks over a distance of 480 m. Three traits were analysed, RT, ranking and a scaled logarithmic function for RT (ART), which was used to adjust racing time to be normally distributed. The data were analysed with a bivariate animal model. The estimated heritabilities were moderate for RT (0.31) and ART (0.38), but very low for ranking (0.10). The repeatabilities were 0.56 (RT), 0.51 (ART) and 0.13 (ranking). The genetic correlations were very high, 0.99 (RT-ranking) and 0.96 (ART-ranking), while the phenotypic correlation was lower, 0.60 (RT-ranking) and 0.62 (ART-ranking). The genetic trend for the traits as well as the phenotypic change of the average RT was positive.     

Career profile of the Canadian Standardbred. I. Influence of age, gait and sex upon chances of racing.

The objective of the present investigation was to provide demographic information regarding the career profile of the average Canadian Standardbred racehorse for application in undergraduate teaching and clinical decision-making. The study population of 762 horses was selected at random from the 1972 registrations of the Canadian Standardbred Horse Society. Sex, birthdate, and province of origin were recorded. Records of racing performance were summarized to provide annual statistics for number of races, money won, race times, and months raced over a ten year period from 1974 to 1983 inclusive. Results were analyzed to determine chances of racing, and the effect of sex, gait, and year of first race upon career duration. Of the 762 horses studied, 507 (66.5%) raced. Mean age at the time of the first race was 3.4 +/- 0.5 years (mean +/- SEM), mean career duration 4.1 +/- 0.1 years. Only 84 horses started racing at two years of age, the majority starting at three and four. Sex had a significant effect upon chances of racing, females having less chance than males or geldings. Females similarly had much shorter careers. As age at the time of the first race increased so did the rate of loss of horses from active competition (attrition rate). The difference between successive years was significant (p less than 0.01). Attrition rates were lower for trotters than for pacers, while geldings showed a significantly lower rate than either males or females (p less than 0.05). Relatively few of those horses for which year of first race was delayed beyond 1974 had been entered in qualifying races in previous years.(ABSTRACT TRUNCATED AT 250 WORDS)     

Factors affecting prerace dehydration and performance of racing greyhounds

Several factors, including age, sex, race number, post position, and race class, were evaluated for relationships to prerace percentage body weight loss and performance in all Greyhounds racing during August 1983 in Oregon. The incidence of percentage body weight loss greater than or equal to 2.5% was low (5%). Race number had a direct effect on weight loss; the later the dogs raced, the more weight loss they experienced. Female dogs were 3 times more likely to lose greater than 2.4% of body weight than males. All dogs experiencing greater than 2.4% body weight loss were 2 times more likely to finish in the first 3 places when racing in the first 5 races overall. In addition, males losing greater than 2.4% of body weight performed better than females when racing together in the final 6 races. Males appeared to be better performers than females, as they were twice as likely to be in class A races. However, once in the race, males and females performed equally.     

Genetic correlations between performance at different racing distances in Thoroughbreds

The aim of the present study was to estimate genetic correlations between time at different racing distances in Thoroughbred racehorses based on data provided by Turftotal Ltda. The traits evaluated were times in seconds for distances of 1000, 1100, 1200, 1300, 1400, 1500 and 1600 m, with a total of 32,145 races and 238,890 time records being analyzed. The (co)variance components necessary to obtain the genetic correlations were estimated using the MTGSAM program in a two-trait animal model. The model used for analysis of the data involved animal and permanent environmental random effects, and race, sex, age and post position at start as fixed effects. All genetic correlations were positive and ranged from medium (0.54) to high (0.93).     

Genetic correlations for foal and studbook traits with racing traits and implications for selection strategies in the Finnhorse and Standardbred trotter

Genetic correlations for body measurements and conformation and functional traits in foals and studbook horses with racing traits were estimated in the Finnhorse and Standardbred. Genetic response and accuracy were estimated using records of animal, half‐sibs and parents in selection scenarios for racing traits, for foal and racing traits, for studbook and racing traits, and using records of animal, half‐sibs and parents for foal traits and racing traits of parents. Racing time and earnings were the breeding objective. Low‐to‐moderate genetic correlations for body measurements and racing traits indicated that selection favours bigger horses at all ages. Being mainly favourable for the breeding objective, genetic correlations for conformation and functional traits with racing traits were highest for the foal traits of type, trot and overall grade and for the studbook traits of character and movements. Genetic correlations for foal and studbook conformation with racing traits were low in the Finnhorse and moderate to high in the Standardbred. In foals, the highest genetic correlations were for trot with racing time (?0.54) and with earnings (0.52) in the Finnhorse, and for overall grade with racing time (?0.54) and with earnings (0.54) in the Standardbred. In studbook horses, genetic correlations were high for character with racing time and earnings in the Finnhorse (?0.68, 0.61) and in the Standardbred (?0.63, 0.70), and for movements with racing time and earnings in the Finnhorse (?0.70, 0.69) and in the Standardbred (?0.90, 0.88). To increase accuracy of conformation and functional traits, foal traits would be more useful in the index with racing traits, as being less preselected than studbook traits. The foal traits (type, trot, overall grade) having moderate heritability and genetic correlations with racing traits would be useful in multi‐trait index before a racing career, where the greatest gain is because of a shorter generation interval. It would be feasible to implement for AI stallions.     

Significance of ossificated ungular cartilages regarding the performance of cold-blooded trotters

Background

Ossification of the ungular cartilages (OUC) in the foot of horses has been studied for more than 100 years. There is a high heritability of this condition but its clinical relevance has remained questionable. Nevertheless, modern equine orthopedic literature ranks OUC as one of top 10 causes of lameness in cold-blooded trotters and stallions of these breeds are excluded from breeding if they have more than mild levels of side bones. Cold-blooded trotters have been used for racing for many decades and official sports data have been available since 1923. A decreased performance is often the only obvious clinical sign noticed by trainers and owners motivating them to seek professional help from veterinarians and farriers. By comparing various performance parameters in Swedish-Norwegian cold-blooded trotters without and with different grades of OUC, we aimed to determine the clinical relevance of ossified hoof cartilages in a population of high-performance horses.Front hooves from 649 Swedish-Norwegian cold-blooded trotters were evaluated radiologically regarding OUC. Breeding index and official sports data originating from strict protocols kept by groups of officials in trotting associations was used for comparison of performance of these horses that together had competed in more than 23,000 races between 1973 and 2009. Generalized linear mixed models were used for the statistical analyses. The response variable was modeled using ordinal logistic models with a multinomial distribution and a cumulative logit link function. The horse was used as a random factor.

Results

Significant effects of gender on performance were demonstrated, but no correlations were found between different positions nor grades of ossified ungular cartilage and number of starts, running pace, race winnings, number of races completed in a regular gait.

Conclusions

Ossification of the ungular cartilages does not cause decreased performance in cold-blooded trotters and is therefore most likely not a cause of clinical or subclinical lameness in this breed. Results from this study can assist equine professionals in evaluating and interpreting the clinical relevance of radiological findings on ossified hoof cartilage among heavy and high-performing horses.     

Sex variation in the prevalence of exercise-induced pulmonary haemorrhage in racing quarter horses

Post race endoscopy was carried out on 255 two-year-old quarter horses and exercise-induced pulmonary haemorrhage (EIPH) was diagnosed in 166 (65 per cent) of them. Visible epistaxis was seen in a higher proportion of geldings than in either mares or stallions. The prevalence of EIPH was similar in mares (73 per cent) and in geldings (74 per cent). A significantly lower prevalence (49 per cent) was noted in stallions (P less than 0.01). It was concluded that a sex variation in the prevalence of EIPH exists in two-year-old quarter horses.     

Estimation of genetic parameters of racing performance in Iranian Thoroughbred horses

The aim of this study was to estimate the genetic parameters of racing performance and investigate the fixed effects that influence the performance of Thoroughbred race horses. The data included the performance of two, three and four year old horses raced in flat races and consisted of 10,800 time records and 10,912 ranking value. Two criteria were used in order to analyze the performance: racing time and a normalized ranking value. The effects of age of horse at racing and post position were significant for all traits (P < 0.05). The effect of hippodrome also was significant for racing time (P < 0.001). The genetic parameters were estimated by the restricted maximum likelihood (REML) method using DFREML program. The heritability estimates for racing time at 1000, 1400 and + 1600 m were 0.13 (± 0.009), 0.11 (± 0.007) and 0.09 (± 0.009) and for ranking value were 0.15 (± 0.010), 0.17 (± 0.008), 0.13 (± 0.009) and 0.11 (± 0.013) for entire data set, 1000, 1400 and + 1600 m respectively. Estimates of repeatability of racing time for 1000, 1400 and + 1600 m were 0.26, 0.19 and 0.17; and for ranking value were 0.28, 0.32, 0.25 and 0.20 for entire data set, 1000, 1400 and + 1600 m respectively. The genetic correlation of two criteria was 0.68–0.79 depended on distances of races.     

Capsule types of Klebsiella pneumoniae isolated from the genital tract of mares with metritis, extra-genital sites of healthy mares and the genital tract of stallions

A survey of K. pneumoniae was performed on cervical swabs, feces and nasal swabs of mares and on samples from the genital tract of stallions from 1980 to 1986 in south-western Hokkaido, Japan. K1 was the predominant type (79 of 88, 89.8%) in the metritis cases due to K. pneumoniae in mares of racing breeds. The same type was isolated from semen and swabs of the fossa glandis of 6 of 20 (30.0%) of the stallions of racing breeds. Heavily encapsulated and less heavily encapsulated K1 strains were isolated from the stallions. Mares bred to stallions carrying heavily encapsulated strains developed metritis, while those bred to stallions carrying less heavily encapsulated strains did not. K39 was isolated from cervical swabs solely from metritis-infected mares of draft breeds and not from any mares of the racing breeds examined. Untypable strains were isolated from cervical swabs in 7 of 88 (8.0%) metritis cases of mares of racing breeds and from semen in 7 of 19 (36.8%) stallions of racing breeds and they were predominant in feces (19 of 21, 90.5%) and nasal swabs (3 of 4, 75.0%) of healthy mares of racing breeds.     

Inheritance of racing performance of Thoroughbred horses

Horse racing is a contest between horses, usually held for the purpose of betting. Thoroughbred horse racing is the most diffused form of horse racing throughout the world. Thoroughbred is one of the most versatile of horse breeds and has influenced the development of many other breeds. Thoroughbred horses served as a foundation stock for the development of the light horse breeds. The two types of horse racing are flat racing and jumping races/steeplechases. The measures of racing performance are broadly classified into three categories. They are time and its several variations, handicap or similar performance ratings and earnings. One common measure of the performance of racehorses evaluated genetically is racing time or final time. The heritability estimates differed according to method of estimation, age, sex, track and distance. Time measure generally had a heritability in the range of 0.1 to 0.2 with the higher values for shorter races. For handicap and earning measures the heritabilities reported were generally higher in the range of 0.3 to 0.4; hence these may be considered in genetic evaluation of racing performance of Thoroughbred horses. The average generation interval of Thoroughbred horses was 11.2 ± 4.5 and 9.7 ± 3.8 years for males and females respectively, which limits the genetic progress in racing horses. However, the major advantage is that the racing performance may be evaluated in both males and females and repeated observations can be obtained on the same animal in relatively short periods. These factors coupled with the reasonable heritability of some measures of racing performance, suggest that mass selection based on performance tests would be the selection procedure of choice to improve the racing performance of Thoroughbred horses. In general, the inbreeding at the rate that is usually practised in Thoroughbred population does not enable much gene fixing. However, practice of close inbreeding may be avoided, even though it still fascinates breeders at subconscious level.     

Association of high-speed exercise with racing injury in thoroughbreds

OBJECTIVE: To determine the association between high-speed exercise and risk of injury while racing among Thoroughbreds in Kentucky. DESIGN: Matched case-control study. ANIMALS: 206 Thoroughbreds that sustained a musculoskeletal injury while racing and 412 Thoroughbreds that were not injured during the same races. PROCEDURE: Data regarding official timed workouts and races and the Beyer's numbers for the 3 races before the race during which injury occurred were extracted from past performance charts and compared between injured horses and control horses. RESULTS: For injured horses, cumulative distance of high-speed exercise during the 1- and 2-month periods prior to the race in which injury occurred was significantly less than that of control horses; for either period, a difference of 10 furlongs was associated with approximately 2-fold greater risk of injury. Beyer's numbers were significantly higher for injured horses than for control horses. These effects remained significant after adjusting for age and results of prerace physical inspection. CONCLUSIONS AND CLINICAL RELEVANCE: In Kentucky, injured horses had significantly less cumulative high-speed exercise than did control horses during the 1- and 2-month periods prior to the race in which injury occurred. These results differ from those observed in California. The association of injury with cumulative high-speed exercise appears to vary among regions in the United States.     

Effect of ‘tongue tie’ use on racing performance of Thoroughbreds in the United Kingdom

Reasons for performing study: There is contradictory published evidence on the potential efficacy of ‘tongue ties’ (TTs) for treatment of intermittent dorsal displacement of the soft palate (DDSP) in racehorses. Objectives: To evaluate the effect of TTs on racing performance in Thoroughbred racehorses in the UK using a retrospective cohort study. Methods: Data on individual horses' lifetime racing performance and TT use were retrieved from the Racing Post Online Database. Exposed cases were horses that ran with a TT in randomly chosen race meetings on one of 60 randomly chosen dates from 2001–2003. Unexposed (control) horses were matched to each exposed horse. Various measures of racing performance were analysed both within and between exposed and unexposed groups. Subsets of exposed horses that ran for 3 or 5 consecutive starts wearing TTs and their matched controls were analysed separately to examine the effect of repeated TT use. Results: The inclusion criteria were fulfilled by 108 horses. The odds ratio for ‘improvement’ in race earnings between exposed and unexposed horses was 1.85 for horses that ran at least once with a TT, and 3.60 and 4.24, respectively, for horses that ran in 3 or 5 consecutive races wearing a TT. After instigation of TT use, horses that ran in 3 or 5 consecutive races wearing a TT had a significant increase in earnings when they ran wearing a TT compared to their pre‐TT races. Conclusions and potential relevance: The use of a TT appears to have a beneficial effect on racing performance in a selected population of Thoroughbred racehorses.