Left ventricular size and systolic function in Thoroughbred racehorses and their relationships to race performance.

Cardiac morphology in human athletes is known to differ, depending on the sports-specific endurance component of their events, whereas anecdotes abound about superlative athletes with large hearts. As the heart determines stroke volume and maximum O(2) uptake in mammals, we undertook a study to test the hypothesis that the morphology of the equine heart would differ between trained horses, depending on race type, and that left ventricular size would be greatest in elite performers. Echocardiography was performed in 482 race-fit Thoroughbreds engaged in either flat (1,000-2,500 m) or jump racing (3,200-6,400 m). Body weight and sex-adjusted measures of left ventricular size were largest in horses engaged in jump racing over fixed fences, compared with horses running shorter distances on the flat (range 8-16%). The observed differences in cardiac morphologies suggest that subtle differences in training and competition result in cardiac adaptations that are appropriate to the endurance component of the horses' event. Derived left ventricular mass was strongly associated with published rating (quality) in horses racing over longer distances in jump races (P < or = 0.001), but less so for horses in flat races. Rather, left ventricular ejection fraction and left ventricular mass combined were positively associated with race rating in older flat racehorses running over sprint (<1,408 m) and longer distances (>1,408 m), explaining 25-35% of overall variation in performance, as well as being closely associated with performance in longer races over jumps (23%). These data provide the first direct evidence that cardiac size influences athletic performance in a group of mammalian running athletes.     

Identification of the myostatin locus (MSTN) as having a major effect on optimum racing distance in the Thoroughbred horse in the USA

One hundred and eighty-nine Thoroughbred horses that had won Graded Stakes races in North America were genotyped with the Illumina Equine SNP50 bead chip. Association tests using PLINK to determine whether any SNPs were associated with optimum racing distance (7 furlongs and under compared to 8-10 furlongs) identified a locus on ECA18 that was statistically significant (-log 10 EMP2=1.63) at the genome-wide level following permutation analysis (10,000 permutations). Bioinformatic analysis revealed that the two ECA18 SNPs with the highest statistical significance spanned the MSTN (myostatin) locus. Mutations in myostatin in several mammalian species have been associated with increased muscling, with a preferential increase in fast glycolytic type IIB fibres, which would increase power potential. Thoroughbred horses that race over sprint distances, which are 5-7 furlongs, are often characterized by impressive hind quarter musculature, strongly suggesting that the association observed between the ECA18 SNPs and optimum race distance is mediated through MSTN.     

Speed, pacing strategy and aerodynamic drafting in Thoroughbred horse racing

Choice of pacing strategy and the benefit of aerodynamic drafting are thought to be key determinants of racing performance. These effects have largely been analysed without reference to final outcome, in small datasets with low temporal resolution, and a focus on human swimming, cycling and running. Here, we determined the position and speed of 44,803 racehorses, once per second, in 3,357 races ranging in length from 1006 to 4225 m (50.9-292.9 seconds duration) using a validated radio tracking system. We find that aerodynamic drafting has a marked effect on horse performance, and hence racing outcome. Furthermore, we demonstrate that race length-dependent pacing strategies are correlated with the fastest racing times, with some horses reaching a maximum speed in excess of 19 m s(-1). The higher speeds seen with certain pacing strategies may arise due to the nature of pack racing itself, or may be a reflection of individual capabilities, that is, corresponding to horses that perform well in roles suited to their 'front-running' or 'chaser' personality traits.     

Leukocyte telomere length in the Thoroughbred racehorse

Thoroughbred racehorses possess superior cardiorespiratory fitness levels and are at the pinnacle of athletic performance compared to other breeds of horses. Although equine athletes have undergone years of artificial selection for racing performance, musculoskeletal injuries and illnesses are common and concerns relating to animal welfare have been proposed. Leukocyte telomere length is indicative of biological age, and accelerated telomere shortening occurs with excess physical and psychological stress. This study was designed to explore the association between leukocyte telomere length, biological factors (age, sex and coat colour), training status, winnings and race history parameters. Blood was collected from 146 Thoroughbred racehorses from around Geelong, Victoria, Australia. DNA was extracted from leukocytes; telomere length was measured using qPCR and analysed in context with traits obtained from the Racing Australia website. Age was inversely correlated with telomere length (r = ?0.194, P = 0.019). The oldest horses (≥11 years) in the highest age quartile possessed shorter telomeres compared to younger horses in the first, second and third quartiles (≤2, 3–5 and 6–10 years respectively; P < 0.05). No statistically significant associations were observed between telomere length and biological factors, training status, winnings or race history parameters in age‐adjusted analyses. The study findings suggest that Thoroughbred horses may undergo age‐related telomere shortening similar to other mixed breeds and humans. Despite concerns from some quarters regarding the welfare of racehorses, there was a lack of accelerated biological ageing observed in the present study, as indicated by leukocyte telomere length.     

Whip use by jockeys in a sample of Australian Thoroughbred races--an observational study

The use of whips by jockeys is an issue. The current study viewed opportunistic high-speed footage of 15 race finishes frame-by-frame to examine the outcomes of arm and wrist actions (n = 350) on 40 horses viewed from the left of the field. Any actions fully or partially obscured by infrastructure or other horses were removed from the database, leaving a total of 104 non-contact sweeps and 134 strikes. For all instances of arm actions that resulted in fully visible whip strikes behind the saddle (n = 109), the outcomes noted were area struck, percentage of unpadded section making contact, whether the seam made contact and whether a visible indentation was evident on impact. We also recorded use of clockwise or counter-clockwise arm action from each jockey''s whip, whether the whip was held like a tennis racquet or a ski pole, whether the hind leg on the side of the impact was in stance or swing phase and whether the jockey''s arm was seen traveling above shoulder height. The goal of the study was to characterize the area struck and the visual impact of whip use at the level of the horse. We measured the ways in which both padded and unpadded sections of the whip made impact. There was evidence of at least 28 examples, in 9 horses, of breaches of the whip rules (one seam contact, 13 contacts with the head, and 14 arm actions that rose above the height of the shoulder). The whip caused a visible indentation on 83% of impacts. The unpadded section of the whip made contact on 64% of impacts. The results call into question the ability of Stewards to effectively police the rules concerning whip use and, more importantly, challenge the notion that padding the distal section of whips completely safeguards horses from any possible whip-related pain.     

Targets of selection in the Thoroughbred genome contain exercise-relevant gene SNPs associated with elite racecourse performance

Athletic performance is influenced by a complex interplay among the environment and a suite of genes, which contributes to system-wide structure and function. In a panel of elite and non-elite Thoroughbred horses (n=148), we genotyped 68 SNPs in 17 putative exercise-relevant genes chosen from a genome scan for selection. We performed a series of case-control and quantitative association tests for relationships with racecourse performance. Thirteen SNPs in nine genes were significantly (P<0.05) associated with a performance phenotype. We selected five SNPs in four genes (ACSS1, ACN9, COX4I1, PDK4) for validation in an independent sample set of elite and non-elite Thoroughbreds (n=130). Two SNPs in the PDK4 gene were validated (P<0.01) for associations with elite racing performance. When all samples were considered together (n=278), the PDK4_ 38973231 SNP was strongly associated (P<0.0005) with elite racing performance. Individuals with the A:A and A:G genotypes had a 16.2-16.6 lb advantage over G:G individuals in terms of handicap rating. Re-sequencing of the PDK4 gene and further genotyping will be required to identify the causative variant that is likely influencing exercise-induced variation in expression of the gene. Notwithstanding, this information may be employed as a marker for the selection of racehorses with the genetic potential for superior racing ability.     

MSTN genotype (g.66493737C/T) association with speed indices in Thoroughbred racehorses

Sequence variation at the equine myostatin gene (MSTN) locus has previously been shown to have a singular genomic influence on optimum race distance in Thoroughbred racehorses. Myostatin, encoded by the MSTN gene, is a member of the TGF-β superfamily that regulates skeletal muscle development in a range of mammalian species including the horse. In the Thoroughbred, the C-allele at the g.66493737C/T SNP has been found at significantly higher frequency in subgroups of the population that are suited to fast, short distance, sprint races and also influences body composition phenotypes. We investigated the influence of the g.66493737C/T SNP on speed indexes measured in a cohort of n = 85 Thoroughbred horses-in-training. We found significant associations between genotypes at the g.66493737C/T SNP and all measured speed variables: Dist(6) [distance travelled during 6 s before and after maximal velocity (V(max)); P = 0.0040], V(maxt) (duration at V(max); P = 0.0249), V(max) (P = 0.0265), Dist(6b) (distance travelled during 6 s before V(max); P = 0.0032), and Dist(6a)(distance travelled during 6 s after V(max); P = 0.0317). For each measure, horses with the C/C and C/T genotypes outperformed T/T horses, indicating the requirement for at least one C-allele to improve speed. For the most significantly associated variables (Dist(6) and Dist(6b)) the C/C cohort performed better than the T/T cohort with the heterozygotes intermediate, indicating a dose-dependent manifestation. These findings clearly indicate that variation at the MSTN gene influences speed in Thoroughbred horses.     

Effects of racing on equine fertility

Racing and fertility are connected with each other in many ways. Stress and increased body temperature induced by racing may have negative effects on fertility, but on the other hand, high quality nutrition and management of racing horses may have positive effects. Fertility may also be genetically associated with racing performance. The analysed data consisted of Finnish mating records of Standardbreds (n=33,679) and Finnhorses (n=32,731), from 1991 to 2005, and the harness racing records of both mares and stallions. Fertility was measured by foaling outcome, and racing performance was measured by best time and number of races. We used racing results from the mating year and from the entire career, to study both short-term and long-term effects of racing on fertility. The analyses were conducted with a linear mixed model, where racing was fitted as a fixed factor. In a separate bivariate analysis we measured the genetic correlation of racing and fertility, applying a threshold model for the fertility trait. For mares, racing after the first mating or more than 10 times during the mating year diminished the foaling outcome. However, racing only before the first mating or 1-5 times during the mating year had positive effects on mare fertility. Stallion fertility did not suffer from racing during the mating year. The mares with the best career racing records had the highest foaling rates, but this was probably due to preferential treatment. The genetic correlation between best racing record and fertility was favourable but weak in the Finnhorse (-0.24±0.08), and negligible in the Standardbred (-0.15±0.11).     

A cohort study of racing performance in Japanese Thoroughbred racehorses using genome information on ECA18

Using 1710 Thoroughbred racehorses in Japan, a cohort study was performed to evaluate the influence of genotypes at four single nucleotide polymorphisms (SNPs) on equine chromosome 18 (ECA18), which were associated in a previous genome‐wide association study for racing performance with lifetime earnings and performance rank. In males, both g.65809482T>C and g.65868604G>T were related to performance rank (P = 0.005). In females, g.65809482T>C (P = 1.76E‐6), g.65868604G>T (P = 6.81E‐6) and g.66493737C>T (P = 4.42E‐5) were strongly related to performance rank and also to lifetime earnings (P < 0.05). When win‐race distance (WRD) among all winning racehorses and best race distance (BRD) among elite racehorses were considered as the phenotypes, significant associations (P < 0.001) were observed for all four SNPs. The favourable race distance of both elite (BRD) and novice racehorses (WRD) was also associated with genotypes in the ECA18 region, indicating the presence of a gene in this region influencing optimum race distance in Thoroughbred racehorses. Therefore, the association with performance rank is likely due to the bias in the race distances. The location of the SNPs within and proximal to the gene encoding myostatin (MSTN) strongly suggests that regulation of the MSTN gene affects racing performance. In particular, the g.65809482T>C, g.65868604G>T and g.66493737C>T SNPs, or their combinations, may be genetic diagnostic markers for racing performance indicators such as WRD and BRD.     

A Sequence Polymorphism in MSTN Predicts Sprinting Ability and Racing Stamina in Thoroughbred Horses

Variants of the MSTN gene encoding myostatin are associated with muscle hypertrophy phenotypes in a range of mammalian species, most notably cattle, dogs, mice, and humans. Using a sample of registered Thoroughbred horses (n = 148), we have identified a novel MSTN sequence polymorphism that is strongly associated (g.66493737C>T, P = 4.85×10⁻⁸) with best race distance among elite racehorses (n = 79). This observation was independently validated (P = 1.91×10⁻⁶) in a resampled group of Thoroughbreds (n = 62) and in a cohort of Thoroughbreds (n = 37, P = 0.0047) produced by the same trainer. We observed that C/C horses are suited to fast, short-distance races; C/T horses compete favorably in middle-distance races; and T/T horses have greater stamina. Evaluation of retrospective racecourse performance (n = 142) and stallion progeny performance predict that C/C and C/T horses are more likely to be successful two-year-old racehorses than T/T animals. Here we describe for the first time the identification of a gene variant in Thoroughbred racehorses that is predictive of genetic potential for an athletic phenotype.     

Prediction of early race starts in Norwegian-Swedish Coldblooded Trotters

Background  

Less than a third of Norwegian-Swedish Coldblooded Trotters (NSCTs) have started racing as three year olds since the year 2000 despite the fact that large sums are paid out as price-money in the three year season. Recruitment races are arranged by the Norwegian Trotting Association (NTA) to stimulate early training. The management of young horses varies considerably and a large majority is reared by amateurs. The aim of the present study was to identify predictors of early race starts in young NSCT horses under field conditions.     

Sclerosis of the Third Carpal Bone

To assess the significance of radiographic signs of sclerosis of the third carpal bone (C3) in young Standardbred trotters in relation to performance, lameness and bone turnover both carpi in 14 Standardbred trotters were radiographically and scintigraphically examined 6 times, from the beginning of speed training until the beginning of racing, between the mean ages of 20 and 42 months. At the end of the study 8 horses had raced in official qualifying races and 14 limbs in 11 horses had been diagnosed with carpal lameness. All horses but 2 developed sclerosis and all but one had increased bone turnover in the C3 area by scintigraphy. C3 sclerosis increased continuously over time and with increased performance. Carpal lameness was significantly associated with progression of sclerosis but in most cases sclerosis developed without concomitant signs of carpal lameness. No association between carpal lameness and increased scintigraphic uptake was found, but horses that had qualified for racing had significantly higher C3 to carpus ratio of radiopharmaceutical uptake. We conclude that there is a continuous increase in C3 radiographic sclerosis with time in young Standardbred trotters in professional training, but radiographic sclerosis appears to be of limited value as an indicator of clinical carpal disease or level of performance in Standardbred trotters.     

Lactate-transport activity in RBCs of trained and untrained individuals from four racing species

In red blood cells (RBC) of horses, both lactate-transport activity and lactate accumulation during races vary interindividually. To study whether similar variation in lactate transport is apparent also in RBCs of other racing species, blood samples were collected from 21 reindeer, 40 horses, 31 humans, and 38 dogs. Total lactate-transport activity was measured at 10 and 30 mM concentrations, and the roles of the monocarboxylate-transporter (MCT) and the inorganic anion-exchange transporter (band-3 protein) were studied with inhibitors. In the reindeer and in one-third of the horses, lactate transport was low and mediated mainly by band-3 protein and nonionic diffusion. In the humans, dogs, and the remaining two-thirds of the horses, lactate transport was high and MCT was the main transporter. No correlation existed between MCT activity and the athleticism of the species. In the horses and humans, training had no effect on lactate transport, but in the reindeer and sled dogs, training increased total lactate transport. These results show that among the racing species studied, only in horses was the distribution of lactate-transport activity bimodal, and the possible connection between RBC lactate and performance capacity, especially in this species, warrants further studies.     

Analysis of selected kinematic and physiological performance determinants during incremental testing in elite swimmers

This study examined the relationships between selected kinematic and physiological parameters and their influence on performance during incremental exercise in elite swimmers competing at the international level. Eleven men and ten women (all specialized in 200-m events) performed an incremental 7 x 200-m test in their specialized stroke. Stroke rate (SR), stroke length (SL), velocity (V), and blood lactate concentration (BLa) were measured for each 200 m. In addition to the cross-sectional group design, the longitudinal performance of a male swimmer was evaluated by 4 tests during a period of 20 weeks. Stroke rate increased and SL decreased with V, regardless of the age, stroke, or gender of the swimmer. Statistically significant correlations were found between SR and V (p < 0.01; r = 0.66 to 0.99), SR and SL (p < 0.01; r = -0.78 to -0.99), SL and V (except for women's freestyle and breaststroke) (p < 0.01; r = -0.67 to -0.98), and BLa and V (p < 0.01; r = 0.7 to 0.96). Changes in SR and SL were not affected by changes in BLa. Similar velocities were produced with different combinations of SR and SL. The fastest times reached in the test were generally slower than expected, and the performance in the test was not associated with competition performance. The case study revealed similar results to those of the group. The test used in this study was informative with respect to identifying the most economical and effective stroke kinematics combination for slow to submaximal velocities. It is possible that the swimming speeds were not maximal in the final 200-m swim because of cumulative fatigue, which is a major limitation for assessing race pace. An additional test that produces velocities similar to those used in competitions would be more useful for the purpose of providing optimal kinematic information specific to racing speeds, which would facilitate performance improvement through regular monitoring in training.     

Genetic profiling of thoroughbred racehorses by microsatellite marker analysis

The thoroughbred (TB) horse breed has exceptional physiological traits and is well-known in horse racing. It has been bred for endurance, strength, and speed for 300 years. Recently, there have been many studies on the molecular characteristics or mechanisms associated with elite athletic performance of the TB breed, and sequence variants in exercise-related genes have also been reported. Here, using 12 microsatellite markers, we assessed genetic diversity and relationships among two groups of TB racehorses (registered by the Seoul Race Park of the Korea Racing Authority) that showed the 48 highest and lowest scores in races. When comparing allelic variation between the highest- and lowest-scoring TB horse groups, a total of 53 different alleles were detected by genotyping with 6′FAM-labelled primers. The genetic variation between the two groups was similar [mean number of alleles (N _A ) = 4.00 and 4.08; allelic richness (A _R ) = 3.95 and 4.01; observed heterozygosity (H _O ) = 0.53 and 0.56, respectively]. However, among the 53 alleles that we assessed, four alleles were detected only in the highest-scoring and five alleles only in the lowest-scoring racing horse group. The group-specific unique alleles indicate that the microsatellite markers could distinguish horses that showed high or low scores in a race. This study demonstrates the feasibility of microsatellite analyses for selection of superior racehorses and suggests further study to understand the relationship between molecular features and phenotype (racing performance).     

中国蒙古马与国外纯血马mtDNA D-Loop高变区序列比较

比较分析了4匹中国蒙古马和4匹国外纯血马的线立体DNA（mtDNA）D-Loop高变区400bp核苷酸序列的变异情况。结果发现,4匹中国蒙古马mtDNA D-Loop高变区的平均核苷酸变异率为3.69%,而纯血马的为4.00%,其核苷酸变异类型均包括转换、颠换和缺失3种形式,其中以转换最为常见。核苷酸变异基因座多,并且存在长度变异,不同变异在个体之间差异也很大,因此说明中国蒙古马和国外纯血马的mtDNA D-Loop高变区都具有丰富的多态性。Abstract：Mitochondrial DNA D-Loop varied region 400bp sequence variations in 4 Chinese Mongolian horses and 4 External Thoroughbred horses were analyzed in this experiment. The results showed that the average nucleotide mutational rate of mtDNA D-Loop varied region in 4 Chinese Mongolian horses was 3.69%,while External Thoroughbred horses were 4.00%. Three types of mutations including transition,transversion and deletion were all found in the investigated mtDNA D-Loop regions,of which transition was the most frequent. Nucleotide mutational loci were abundant,length mutations were found and great differences were all observed among the 8 horses. It showed there existed much polymorphism in the mitochondrial DNA D-Loop varied region of Chinese Mongolian horses and External Thoroughbred horses.     

Does heterozygosity at the DMRT3 gene make French trotters better racers?

Background

Recently, a mutation was discovered in the DMRT3 gene that controls pacing in horses. The mutant allele A is fixed in the American Standardbred trotter breed, while in the French trotter breed, the frequency of the wild-type allele C is still 24%. This study aimed at measuring the effect of DMRT3 genotypes on the performance of French trotters and explaining why the polymorphism still occurs in this breed. Using a mixed animal model, genetic parameters and environmental effects on performance traits were estimated from data on 173 176 French trotter races. The effect of the DMRT3 gene was then estimated by the effect of genotype at the highly linked SNP BIEC2-620109 (C-C, A-T) for 630 horses. A selection scheme that included qualification and racing performances was modeled to (1) verify if the observed superiority of heterozygous CT horses at this SNP could be explained only by selection and (2) understand why allele C has not disappeared in French trotters.

Results

Heritability of racing performance traits was high for qualification test (0.56), moderate for annual earnings per finished race (0.26 to 0.31) and low for proportion of disqualified races (0.06 to 0.09). Genotype CC was always unfavorable compared to genotype TT for qualification: the probability to be qualified was 20% for CC vs. 48% for TT and earnings were -0.96 σ_y lower for CC than for TT. Genotype CT was also unfavorable for qualification (40%) and earnings at 3 years (-0.21 σ_y), but favorable for earnings at ages greater than 5 years: +0.41 σ_y (P = 7.10⁻⁴). Selection on qualification could not explain more than 19% of the difference between genotypes CC and CT in earnings at ages greater than 5 years. Only a scenario for which genotype CT has a favorable effect on the performance of horses older than 5 years could explain that the polymorphism at the DMRT3 gene still exists in the French trotter breed.

Conclusions

The use of mature horses in the French racing circuit can explain that the CA genotype is still present in the French trotter horses.     

Biochemical polymorphism in relation to performance in horses

Summary Investigations on relationships between biochemical polymorphism and variation in quantitative traits are of interest from the perspectives of both theoretical quantitative genetics and practical animal breeding. This subject was studied by using racing performance records of more than 25,000 horses of the Swedish Trotter breed born in the period 1970–1979. For all horses data on six blood group and nine electrophoretic loci were available. Two different performance traits were investigated. A racing performance index value was calculated for all individuals which had started in at least five races. Horses which had not started at all or less than five times were pooled in an unstarted class and the proportion of started horses was analysed as an all-or-none trait. The relationships between the marker genes and these two performance traits were analysed statistically by using linear models. Analysis within sires revealed a very highly significant association between variation at the serum esterase locus (Es) and the proportion of started horses. In addition, four weakly significant associations were found. A striking feature of the highly significant association involving the esterase locus was that the effect of different alleles showed a good fit to an additive genetic model as the value of each heterozygous type was intermediate to the two corresponding homozygotes. In addition to the association tests, the possibility of genetic linkage between marker genes and genes affecting performance was tested as well as the influence on performance of heterozygosity at marker loci. No significant relationships were revealed in these latter tests.     

Distribution of erythrocyte carbonic anhydrase B-type alleles in Japanese farm horses

A study of the erythrocyte carbonic anhydrases of 330 Japanese horses revealed the presence of six major enzymes. All horses possessed a single C-type enzyme. Thoroughbred racing horses had only the B-type carbonic anhydrase designated as D, but some farm horses also had others with electrophoretic mobilities corresponding to the human B, A, and T enzymes. A study of the distribution of these B-type allelic products indicated that their synthesis is controlled by a pair of codominant autosomal alleles as previously reported for the horse and other species.This work was supported in part by Grant No. C-1786 from the U.S. Public Health Service and by the Japan Society for the Promotion of Science.Visiting professor.     

Genetic evaluation of performance traits in Brazilian Quarter Horse

The aim of this study was to estimate genetic parameters for racing performance traits in Quarter Horses in Brazil. The data (provided by the Sorocaba Jockey Club) came from 3 Brazilian hippodromes in 1994-2003, with 11 875 observations of race time and 7775 of the speed index (SI), distributed in 2403 and 2169 races, respectively. The variance components were estimated by the MTGSAM program, under animal models including the random additive genetic effect, random permanent environmental effect, and the fixed effects of sex, age and race. Heritabilities for race time and the SI, for the 3 distances studied (301, 365 and 402 m), varied from 0.26 to 0.41 and from 0.14 to 0.19, respectively, whereas repeatabilities varied from 0.36 to 0.68 (time) and from 0.27 to 0.42 (SI) and the genetic correlations from 0.90 to 0.97 (time) and from 0.67 to 0.73 (SI).