Racing Performance Traits Research Articles

A genome-wide association study of the racing performance traits in Yili horses based on Blink and FarmCPU models

Racing performance traits are the main indicators for evaluating the performance and value of sport horses. The aim of this study was to identify the key genes for racing performance traits in Yili horses by performing a genome-wide association study (GWAS). Breeding values for racing performance traits were calculated for Yili horses (n = 827) using an animal model. Genome-wide association analysis of racing performance traits in horses (n = 236) was carried out using the Blink, and FarmCPU models in GAPIT software, and genes within the significant regions were functionally annotated. The results of GWAS showed that a total of 24 significant SNP markers (P < 6.05 × 10− 9) and 22 suggestive SNP markers (P < 1.21 × 10− 7) were identified. Among them, the Blink associated 16 significant SNP loci and FarmCPU associated 12 significant SNP loci. A total of 127 candidate genes (50 significant) were annotated. Among these, CNTN6 (motor coordination), NIPA1 (neuronal development), and DCC (dopamine pathway maturation) may be the main candidate genes affecting speed traits. SHANK2 (neuronal synaptic regulation), ISCA1 (mitochondrial protein assembly), and KCNIP4 (neuronal excitability) may be the main candidate genes affecting ranking score traits. A common locus (ECA1: 22698579) was significantly associated with racing performance traits, and the function of the genes at this locus needs to be studied in depth. These findings will provide new insights into the detection and selection of genetic variants for racing performance and will help to accelerate the genetic improvement of Yili horses.

Racing Performance of the Quarter Horse: Genetic Parameters, Trends and Correlation for Earnings, Best Time and Time Class.

The aim of this study was to evaluate the sprint racing performance of Quarter Horses in Brazil. Estimating genetic parameters, trends and correlations were obtained by single- and two-trait analyses using Bayesian inference (earnings to 2 years of equestrian age, best time and time class at distances of 301 m and 402 m). The data comprised a period of 38 equestrian years (1978 to 2015) with 23,482 sprint race records from 5861 animals. The heritability estimates were of low to moderate magnitude, ranging from 0.10 to 0.37 (single-trait) and from 0.15 to 0.41 (two-traits), and the repeatability was 0.31 to 0.46. The additive, residual and phenotypic correlations between earnings to 2 years of equestrian age and the other traits (best time and time class in distances 301 m and 402 m) were high (-0.95, -0.96, 0.69 and 0.92), low (-0.29, -0.37, 0.26 and 0.27) and moderate (-0.41, -0.47, 0.37 and 0.47), respectively. There is a positive genetic trend for all traits considered. However, evaluation of the last 10 equestrian years (2006 to 2015) showed negative trends (genetic loss) and trends close to zero (genetic stagnation). The design of breeding programs using the earnings trait in conjunction with other racing performance traits can enhance changes in the genetic gains as a whole in speed-racing Quarter Horses. These findings suggest that the traits studied should be included in breeding selection programs for racing Quarter Horses.

Variation in the SLC16A1 and the ACOX1 Genes Is Associated with Gallop Racing Performance in Arabian Horses

Arabian horses are not only one of the most ancient breeds in the world, but they are also one of the most appreciated racehorse breeds today. The breed generates attention for their phenomenal endurance ability and their capability for gallop racing. Consequently, genetic testing to select the best individuals is attracting ever increasing interests from the Arabian industry. As such, the aim of this study was to further investigate associations between performance and variation at candidate genes suspected of having a key role in Arabian gallop racing performance. Generalized linear models were fit to test associations between eight candidate gene variants and a variety of gallop racing performance traits in a sample of Arabian racehorses (n = 287). Two genes, solute carrier family 16 member 1 (SLC16A1) and acyl-CoA oxidase 1 (ACOX1), were significantly associated with multiple gallop racing performance traits, whereas another gene, actinin alpha 3 (ACTN3) was associated with best race distance. Previously established associations between these three genes and equine metabolism strongly suggest further investigation of these genes, and their relationship with Arabian horse performance is warranted.

A candidate-SNP retrospective cohort study for fracture risk in Japanese Thoroughbred racehorses.

Fractures are medical conditions that compromise the athletic potential of horses and/or the safety of jockeys. Therefore, the reduction of fracture risk is an important horse and human welfare issue. The present study used molecular genetic approaches to determine the effect of genetic risk for fracture at four candidate SNPs spanning the myostatin (MSTN) gene on horse chromosome 18. Among the 3706 Japanese Thoroughbred racehorses, 1089 (29.4%) had experienced fractures in their athletic life, indicating the common occurrence of this injury in Thoroughbreds. In the case/control association study, fractures of the carpus (carpal bones and distal radius) were statistically associated with g.65809482T/C (P=1.17 x 10-8 ), g.65868604G/T (P=2.66 x 10-9 ), and g.66493737C/T (P=6.41 x 10-8 ). In the retrospective cohort study using 1710 racehorses born in 2000, the relative risk (RR) was highest for male horses at g.65868604G/T, based on the dominant allele risk model (RR=2.251, 95% confidence interval 1.407-3.604, P=0.00041), and for female horses at g.65868604G/T, based on the recessive allele risk model (RR=2.313, 95% confidence interval 1.380-3.877, P=0.00163). Considering the association of these SNPs with racing performance traits such as speed, these genotypes may affect the occurrence of carpus fractures in Japanese Thoroughbred racehorses as a consequence of the non-genetic influence of the genotype on the distance and/or intensity of racing and training. The genetic information presented here may contribute to the development of strategic training programs and racing plans for racehorses that improve their health and welfare.

The Genetics of Racing Performance in Arabian Horses.

Arabian horses are commonly believed to be one of the oldest and most influential horse breeds in the world. The high financial benefits obtained from races tend to search for genetic markers strongly correlated with the results achieved. To date, the modern approaches such as transcriptome, miRNAome, and metabolome analyses have been used to investigate the genetic background of racing performance as well as endurance capacity in Arabians. The analysis of polymorphisms at the genome level has also been applied to the detection of genetic variants associated with exercise phenotype in the Arabian breed. The presented review summarizes these findings, with a focus on the genetics underlying flat racing and endurance performance traits in different Arabian horse populations.

Sequence analysis and expression profiling of the equine ACTN3 gene during exercise in Arabian horses

The ACTN3 gene codes for α-actinin-3, a protein localized in the Z-line in the skeletal muscle. Actinin-3 is critical in anchoring the myofibrillar actin filaments and plays a key role in muscle contraction. ACTN3 (α-actinin-3) cross-links glycogen phosphorylase (GP), which is the key enzyme catalysing glycogen metabolism. The aim of present study was to establish the expression level of the ACTN3 gene (for both isoforms separately and together in the gene expression analysis) in the gluteus medius muscle in order to verify if the α-actinin-3 gene can be related to training intensity in Arabian horses. A structural analysis of the ACTN3 gene was performed simultaneously to identify polymorphisms that can be related to racing performance traits. Our results showed the significant decrease (p < 0.05) of ACTN3 expression in the skeletal muscle of Arabian horses during the training periods preparing for flat-racing, and this decrease differed by the intensity of the exercises. The highest mRNA abundance measured for all ACTN3 genes was detected in the muscle of untrained horses, while the lowest expression was identified at the end of the racing season when horses had fully adapted to the physical effort. This gene expression profile was confirmed for both ACTN3 isoforms. The analysis of the ACTN3 sequence allowed us to identify 14 polymorphisms, which were localized in the promoter region, the 5′UTR (7 SNPs), exons (2 SNPs) and introns (5 SNPs). Two of them, a novel c.2334C>T - splice variant and the g.1104G>A polymorphism in the promoter region, were proposed as the causative mutations that might affect gene expression. The presented gene expression analyses indicated the significant role of the ACTN3 gene in adaptation to physiological effort in horses. Due to previous reports and our findings, further studies should be conducted to verify the usage of the ACTN3 gene as a potential genetic marker for determining exercise performance in Arabian horses and other horse breeds.

A genome-wide association study for harness racing success in the Norwegian-Swedish coldblooded trotter reveals genes for learning and energy metabolism

BackgroundAlthough harness racing is of high economic importance to the global equine industry, significant genomic resources have yet to be applied to mapping harness racing success. To identify genomic regions associated with harness racing success, the current study performs genome-wide association analyses with three racing performance traits in the Norwegian-Swedish Coldblooded Trotter using the 670 K Axiom Equine Genotyping Array.ResultsFollowing quality control, 613 horses and 359,635 SNPs were retained for further analysis. After strict Bonferroni correction, nine genome-wide significant SNPs were identified for career earnings. No genome-wide significant SNPs were identified for number of gallops or best km time. However, four suggestive genome-wide significant SNPs were identified for number of gallops, while 19 were identified for best km time. Multiple genes related to intelligence, energy metabolism, and immune function were identified as potential candidate genes for harness racing success.ConclusionsApart from the physiological requirements needed for a harness racing horse to be successful, the results of the current study also advocate learning ability and memory as important elements for harness racing success. Further exploration into the mental capacity required for a horse to achieve racing success is likely warranted.

Molecular characterization of the apoptosis-related SH3RF1 and SH3RF2 genes and their association with exercise performance in Arabian horses

BackgroundApoptosis plays an important role in the regulation of healthy tissue growth and development as well as in controlling the maintenance of homeostasis in exercising muscles. During an intensive physical effort, the regulation of cell death by apoptosis results in the replacement of unaccustomed muscle cells by new cells that are better suited to exercise. The aim of this study was to determine the expression of two genes (SH3FR1 and SH3RF2) that control apoptosis in muscle tissues during training periods characterized by different intensities. The gene expression levels were estimated using real-time PCR method in skeletal muscle biopsies collected from 15 Arabian horses (untrained, after an intense gallop phase, and at the end of the racing season). An association study was performed on 250 Arabian horses to assess the effect of the SH3RF2:c.796 T > C (p.Ser266Pro) variant on race performance traits in flat gallop-racing.ResultsA gene expression analysis confirmed a significant decrease (p < 0.01) in the anti-apoptotic SH3RF2 (POSHER) gene during training periods that differed in intensity. The highest SH3RF2 expression level was detected in the muscles of untrained horses, whereas the lowest expression was identified at the end of the racing season in horses that were fully adapted to the exercise. A non-significant decrease in SH3RF1 gene expression following the training periods was observed. Moreover, a serine substitution by proline at amino acid position 266 (CC genotype) was negatively associated with the probability of winning races, the number of races in which a horse occurred and the financial value of the prizes. Horses with the TT genotype achieved the highest financial benefits, both for total winnings and for winnings per race in which the horses participated.ConclusionsThe present study showed the supposed regulation mechanism of exercise-induced apoptosis in horses at the molecular level. The identified SH3RF2: c.796 T > C missense variant was associated with selected racing performance traits, which is important information during the evaluation of horses’ exercise predisposition. The association results and frequencies of the CT and TT genotypes suggest the possibility of using SH3RF2 variant in selection to improve the racing performance of Arabian horses.

36 The DMRT3 “Gait keeper” mutation affects harness racing performance and riding traits in Finnhorses

s / Journal of Equine Veterinary Science 35 (2015) 398e399 399 36 The DMRT3 “Gait keeper” mutation affects harness racing performance and riding traits in Finnhorses K. J€aderkvist*, L. Johansson , A. Mykk€ anen , M. M€aenp€ a€ a , L.S. Andersson , L. Andersson , T. Arnason , and G. Lindgren 1 1 Swedish University of Agricultural Sciences, Uppsala, Sweden; University of Helsinki, Helsinki, Finland; 3 Suomen Hippos ry, Espoo, Finland; Uppsala University, Uppsala, Sweden; 5 IHBC AB, Knubbo, Morgongava, Sweden The DMRT3 “Gait keeper”mutation is well known for its effects on gaits and locomotion patterns in horses. Previous studies have shown the mutation to have a strong favorable effect on harness racing performance in Standardbreds, French and Nordic trotters. The mutation also affects riding traits in Icelandic horses and in Standardbreds. The aim of this study was to investigate the effect of the DMRT3mutation on harness racing performance and riding traits in Finnhorses. We genotyped for the DMRT3 mutation 180 Finnhorses of trotting type and 59 Finnhorses used for riding. For the trotters the genotypes were evaluated for association with racing performance traits (number of starts, victories, placings, earnings and race times) at different ages. For the Finnhorses used for riding the owners answered a 12 question survey about their horse and had to score how well the horse performed the gaits walk, trot and canter on a scale from 1 to 6. T€ olt and pace ability was also reported. These scores were then tested for an association with the DMRT3 genotypes. Racing performance analyses were performed usingWald tests in PLINK. Fisher's exact tests in R were used for analyses on t€ olt and pace ability, while pairwise t-tests were used for gait score analyses. The results showed that the DMRT3 mutation strongly influenced racing performance in Finnhorses. Between 3 and 6 years of age AA horses had a significantly higher proportion of victories (P1⁄4 1.4 10 6) and placings (P 1⁄4 4.1 10 7) compared with Chorses. Additionally, they also had better race times (P 1⁄4 0.01) and earned more money (P 1⁄4 0.009). Despite CA horses not performing as well as AA horses, they still performed better than CC horses. Thus supporting an additive genetic effect of the DMRT3 mutation on racing performance. Similar results were found when comparing performance at different ages (4, 5, 6 and 10 years), except for 3 years of age where no significant differences were present. Although AA horses were more successful as racehorses, the Chorses appear more adapted for classical riding disciplines. This is supported by significantly lower gait scores for AA horses compared with Chorses for the majority of gaits. With the exception of rhythm in extended canter (P 1⁄4 0.05), no significant differences were present between CA and CC horses for gait scores. A significant association (P 1⁄4 0.006) between DMRT3 genotype and the ability to show t€ olt was present; however, no significant association was present for pace (P 1⁄4 0.21). This study shows that different genotypes are optimal for different disciplines and the DMRT3 mutation clearly influences the pattern of locomotion in Finnhorses.

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

BackgroundRecently, 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.ResultsHeritability 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 σy lower for CC than for TT. Genotype CT was also unfavorable for qualification (40%) and earnings at 3 years (-0.21 σy), but favorable for earnings at ages greater than 5 years: +0.41 σy (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.ConclusionsThe use of mature horses in the French racing circuit can explain that the CA genotype is still present in the French trotter horses.

Heritability of racing performance in the Australian Thoroughbred racing population.

Performance data for 164,046 Thoroughbreds entered in a race or official barrier trial in Australia were provided by Racing Information Services Australia. Analyses estimating the heritability for a range of racing performance traits using a single-trait animal model were performed using ASREML-R. Log of cumulative earnings (LCE; 0.19 ± 0.01), log of earnings per race start (0.23 ± 0.02) and best race distance (0.61 ± 0.03) were all significantly heritable. Fixed effects for sex were significant (P < 0.001) for all performance traits aside from LCE (P = 0.382). With the exception of annual earnings, trainer was also significant for all performance traits. As the application of modern genetic selection methodologies continues to gain popularity in the racing industry, contemporary heritability estimates from the current population of Thoroughbreds will play a vital role in identifying which traits are better suited to selection and in the development of more accurate genomic evaluations for racing performance.

Performance selection for Thoroughbreds racing in Hong Kong

Different indicators of racing performance are commonly used in the racing industry to assess the genetic superiority of racing Thoroughbreds. However, how well these indicators predict the performance of future progeny or siblings varies depending on the population and circumstances in which the indicators were recorded or achieved. To identify heritable indicators of racing performance for horses racing in Hong Kong. Heritability analysis of racing performance traits. Performance data on the population of Thoroughbreds racing in Hong Kong between 3 September 2000 and 12 March 2011 (n = 4947) were acquired and used to estimate the heritabilities and probability values of fixed effects and covariates for a range of racing performance traits. Heritabilities for all performance traits were estimated using a single trait animal model. Each model included, as a minimum, the effects of sex, region of origin and trainer. Heritability estimates for traits relating to finish position ranged from 0.01 to 0.06. Average handicap weight had a heritability of 0.07 ± 0.03. The effects of sex (fixed) and trainer (random) were significant (P<0.05) for all performance traits relating to earnings measures, handicap weights and finish positions. The heritability of win time at 1600 m was 0.52 ± 0.06 and was the only significant estimate of heritability for win time in the current study. Although significantly affected by multiple environmental factors, certain indicators of Hong Kong racing performance can be reliably used to predict the performance of the individual's progeny or siblings. However, despite Hong Kong's controlled racing environment, these indicators appear to be no more heritable than in other less controlled racing environments.

Estimation of Genetic Parameters for Finished and Furlong Times in Thoroughbred Racehorses

The objective of this study was to estimate genetic parameters for racing performance traits of thoroughbred racehorses, using a total of 58,124 racing records of 4,200 horses at Gwacheon Racing Park collected from January 2002 to December 2006. This study measured start one furlong time, last three and last one furlong times, and the resulting furlong time averages were 14.2 seconds, 39.9 seconds and 13.9 seconds, respectively. Furlong time means a split time measured based on a 1/8-mile (or approximately 201 m) distance and finished time means total racing time measured from start position to finish line. In the shortest distance races of 1,000 m, the average last three and last one furlong time was fastest at 38.7 seconds and 13.6 seconds, respectively. The correlation between finished time and start one furlong time decreased as the race distance increased, and the same trend was recognized from the correlation between finished time and last three furlong time. In short distance races of 1,400 m or less, the starting ability was found to be an important trait. The average speed was highest at 56 km/h for a 1,000 m race and lowest at 53.2 km/h for a 1,700 m race. Heritabilities of the start one furlong time, the last three and last one furlong time were estimated to be 0.337, 0.245 and 0.210, respectively; and repeatabilities for them were 0.452, 0.353 and 0.309, respectively. Phenotypic and genetic correlations between the

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.

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).

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

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 parameters of racing performance traits of Quarter horses in Brazil

The data used in the present study were recorded at the Jockey Club of Sorocaba for 5094 racing performance of 1350 Quarter Horses at the Paulista Race Track of Sorocaba, state of São Paulo, Brazil, from 1991 to 1997. The considered traits were time and final rank. The model used in analysis included random animal and permanent environmental effects, and race, sex, age and origin as fixed effects. The variance and covariance components were estimated by the restricted maximum likelihood for an animal model, using the derivative‐free process method and the MTDFREML software. For the time, heritability was 0.17 (0.05), while estimate of repeatability 0.55 (0.05). The lower heritability for the final rank, 0.13 (0.04), indicate that this trait is not the most appropriate one for inclusion in programs of Quarter horse selection in Sorocaba racetrack. The repeatability estimate for rank was 0.44 (0.04) and the genetic correlation between this trait and time was 0.99.

Genetic evaluation of Swedish standard‐bred trotters for racing performance traits and racing status

IntroductionThe BLUP methodology has been applied to the genetic evaluation of Swedish standard‐bred trotters for well over a decade. Initially a BLUP sire model was applied for evaluating breeding values of stallions on the basis of the racing performance of their offspring (Árnason et al. 1989). In 1992 an animal model (AM‐) BLUP was introduced and official publication of index values were offered as an aid for effective selection of stallions and brood mares (Árnason 1992; Árnason and S vendsen 1991). The implementation of the BLUP animal model index has apparently caused profound enhancement in the selection intensity for both stallions and mares (Árnason 1997). The AM‐BLUP evaluation has involved the following traits, which were all based on accumulated racing results as 3‐ to 5‐year‐olds: Number of races (starts); % of races ranked first to third at the finish (i.e. placed first to third); earnings per race; total earnings; best racing time per km; and racing (or start) status, which is denoted as one if the horse did race at least once as a 3‐ to 5‐year‐old and zero otherwise. The two traits: number of races and racing status were initially treated as single traits, in the AM‐BLUP analyses, uncorrelated with the other racing performance traits. Those other traits are direct measures of racing performance for horses that have actually competed on the race track. They are highly intercorrelated and have been treated as a multivariate complex in the analyses. The computational load of general multivariate analyses has been considerably reduced by transformation of the records into uncorrelated canonical variates (e.g. Árnason 1982).In Sweden, about 40% of standard‐bred trotters do not enter a race course and their racing performance variables have previously been treated as missing. Early analysis on the population of standard‐bred trotters in Sweden did not show any correlation between racing status of brood mares and the racing performance of their offspring (M. B endroth, unpublished results). That gave justification for assuming that racing status had mainly environmental causes, and to be practically genetically uncorrelated with performance. The exclusion of nonracers (nonstarters) was therefore not expected to bias genetic evaluations for the performance traits. The expansion of the population during the 1980s and the early 1990s, and increase in the level of prize money, has probably invalidated the implication of these results and partly changed the racing status into a preselection criterion for racing performance. K lemetsdal (1992) has clearly illustrated that such a culling process can result in substantial bias in estimated breeding values. In 1995 a new enhanced procedure replaced the older version used for routine genetic evaluation of Swedish standard‐bred trotters, with the aim of eliminating, or at least reducing, the selection bias and increasing the accuracy in the genetic evaluations.The main objective of this paper was to describe the enhanced procedure for genetic evaluation of Swedish standard‐bred trotters where racing status and racing performance traits were treated in a complete multiple trait framework. The task was made computationally feasible by the application of a procedure which allows solution of multiple trait AM‐BLUP with missing data on some traits using multiple step canonical transformation of records and solutions during the iterative solution phase (D ucrocq and B esbes 1993). The pertinence of the method for establishing a sound selection criterion was verified by stochastic simulations on simplified data structures. The second objective of this study was to evaluate the model and assess the set of genetic parameters used in the BLUP analysis, by linear regressions of the genetic predictions based on the most recent data on genetic predictions obtained in subsamples of the whole data set (method R, R everter et al. 1994a, b).