N. A. Hamilton

The association of age at first start with career length in the Australian Thoroughbred racehorse population

REASONS FOR PERFORMING STUDY Studies of Thoroughbred racing populations have provided evidence of a positive effect on racing careers for horses that commence racing as 2-year-olds. Currently, research investigating the presence of this effect in the Australian Thoroughbred racing population is limited. OBJECTIVES To investigate the association between age at first start and career length in the Australian Thoroughbred population and estimate the risk of racing retirement for horses racing in Australia based on age at first start, career earnings, number of starts as a 2-year-old and distance raced. METHODS Data were collected for Thoroughbreds, born on or after 1 January 1998, that had raced between 1 August 2000 and 22 February 2011 in Australia. A Kaplan-Meier survival curve, stratified by age group, was produced for career length. A Cox proportional hazard model was fitted to assess factors influencing the risk of retirement from racing. The model included sex, age at first start, career earnings, number of starts as a 2-year-old, distance raced and appropriate interaction terms. RESULTS The study population included 117,088 horses. Geldings had significantly (P<0.001) longer careers than females and intact males, and females had significantly (P<0.001) longer careers than intact males. Risk of retirement from racing decreased with a younger age at first start, a higher number of starts as a 2-year-old, and a longer average distance raced. For intact males, the risk of retirement from racing increased as earnings increased, while for females and geldings the risk of retirement from racing decreased as earnings increased. CONCLUSIONS AND POTENTIAL RELEVANCE The introduction of young Thoroughbreds to racing appears to have no apparent adverse effects on these horses racing in Australia. The impact of some risk factors associated with retirement from racing varied between sexes and should be considered when evaluating career outcomes.

The association of age at first start with career length in the Australian racehorse population

REASONS FOR PERFORMING STUDY Studies of Thoroughbred racing populations have provided evidence of a positive effect on racing careers for horses that commence racing as 2-year-olds. Currently, research investigating the presence of this effect in the Australian Thoroughbred racing population is limited. OBJECTIVES To investigate the association between age at first start and career length in the Australian Thoroughbred population and estimate the risk of racing retirement for horses racing in Australia based on age at first start, career earnings, number of starts as a 2-year-old and distance raced. METHODS Data were collected for Thoroughbreds, born on or after 1 January 1998, that had raced between 1 August 2000 and 22 February 2011 in Australia. A Kaplan-Meier survival curve, stratified by age group, was produced for career length. A Cox proportional hazard model was fitted to assess factors influencing the risk of retirement from racing. The model included sex, age at first start, career earnings, number of starts as a 2-year-old, distance raced and appropriate interaction terms. RESULTS The study population included 117,088 horses. Geldings had significantly (P<0.001) longer careers than females and intact males, and females had significantly (P<0.001) longer careers than intact males. Risk of retirement from racing decreased with a younger age at first start, a higher number of starts as a 2-year-old, and a longer average distance raced. For intact males, the risk of retirement from racing increased as earnings increased, while for females and geldings the risk of retirement from racing decreased as earnings increased. CONCLUSIONS AND POTENTIAL RELEVANCE The introduction of young Thoroughbreds to racing appears to have no apparent adverse effects on these horses racing in Australia. The impact of some risk factors associated with retirement from racing varied between sexes and should be considered when evaluating career outcomes.

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.

Profiling the careers of Thoroughbred horses racing in Australia between 2000 and 2010

REASONS FOR PERFORMING STUDY Research investigating trends in racehorse careers require a benchmark for accurate comparison. Currently little whole population data exists for horses racing in Australia. OBJECTIVES To determine the range and variation in career length and number of career starts for horses racing in Australia. To document and provide evidence regarding the current differences between the sexes for career length and careers starts. METHODS Racing data were collected for Thoroughbreds over a 10-year period. Career length, number of career starts and spells per year were evaluated. Statistical analyses were performed using the statistical package R. RESULTS A total of 2,782,774 performance records yielded career information for 164,046 horses. Median career length and number of career starts for the population were 14.7 months and 10 starts, respectively. Significant differences (P<0.001) were present between the sexes for all career outcomes. Between 2000 and 2010, the percentage of Thoroughbreds racing in Australia with careers longer than 12, 24, 36 and 48 months was 56.65, 32.35, 16.66 and 7.74, respectively. CONCLUSIONS AND POTENTIAL RELEVANCE Clear differences in career outcomes exist between intact males, females and geldings racing in Australia. Future research should be conscious of these differences when analysing population data.

Performance selection for Thoroughbreds racing in Hong Kong

REASONS FOR PERFORMING STUDY 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. OBJECTIVES To identify heritable indicators of racing performance for horses racing in Hong Kong. STUDY DESIGN Heritability analysis of racing performance traits. METHODS 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. RESULTS 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. CONCLUSIONS Although significantly affected by multiple environmental factors, certain indicators of Hong Kong racing performance can be reliably used to predict the performance of the individuals progeny or siblings. However, despite Hong Kongs controlled racing environment, these indicators appear to be no more heritable than in other less controlled racing environments.

Heritability of racing durability traits in the Australian and Hong Kong Thoroughbred racing populations

REASONS FOR PERFORMING STUDY Many attempts have been made to improve the well-being of racing Thoroughbreds through improvements in management and veterinary care. However, these attempts are often limited by the industrys ability to regulate a large number of environmental variables and as a result have arguably had limited success in providing long-lasting change for the breed. OBJECTIVES To identify heritable durability traits for Thoroughbred horses racing in Australia and Hong Kong. STUDY DESIGN Heritability analysis of a longitudinal dataset. METHODS Performance data on the Thoroughbred populations racing in Australia and Hong Kong between 2000 and 2011 (n = 168,993) were used to estimate the heritabilities and probability values of fixed effects and covariates for a range of racing durability traits. Heritabilities for all durability traits were estimated using a single trait animal model. Each model included, as a minimum, the effects of sex and trainer. RESULTS Racing longevity (0.12 ± 0.01), racing persistence (0.10 ± 0.01), racing frequency (0.03 ± 0.01), spells (a time period between consecutive races, official trials and/or jump-outs greater than 90 days in length) per year (0.05 ± 0.01), spells per 10 starts (0.03 ± 0.01) and variation of days between races (0.08 ± 0.03) were all significantly heritable for horses racing in Australia. Racing longevity (0.08 ± 0.02), racing persistence (0.04 ± 0.02), spells per year (0.06 ± 0.02) and spells per 10 starts (0.11 ± 0.04) were significantly heritable for horses racing in Hong Kong. CONCLUSIONS The heritabilities estimated for durability traits in this study provide support for the successful and practical application of genetic selection methodologies to improving the well-being of racing Thoroughbreds.

Sequence analysis of the equine ACTN3 gene in Australian horse breeds

The sarcomeric α-actinins, encoded by the genes ACTN2 and ACTN3, are major structural components of the Z-line and have high sequence similarity. α-Actinin-2 is present in all skeletal muscle fibres, while α-actinin-3 has developed specialized expression in only type 2 (fast, glycolytic) fibres. A common single nucleotide polymorphism (SNP) in the human ACTN3 gene (R577X) has been found to influence muscle performance in elite athletes and the normal population. For this reason, equine ACTN3 (eACTN3) is considered to be a possible candidate that may influence horse performance. In this study, the intron/exon boundaries and entire coding region of eACTN3 have been sequenced in five Australian horse breeds (Thoroughbred, Arabian, Standardbred, Clydsdale and Shire) and compared to the eACTN3 GenBank sequence. A total of 34 SNPs were identified, of which 26 were intronic and eight exonic. All exonic SNPs were synonymous; however, five intronic SNPs showed significant differences between breeds. A total of 72 horses were genotyped for a SNP located in the promoter region of the eACTN3 gene (g. 1104 G>A) which differed significantly between breed groups. We hypothesize that this polymorphism influences eACTN3 expression and with further studies may provide a novel marker of horse performance in the future.

Profiling the careers of Thoroughbred horses racing in Hong Kong between 2000 and 2010.

REASONS FOR PERFORMING STUDY Research in Thoroughbred racehorses is often specific to horses from a given racing population or region. In order to investigate trends in racehorse careers across populations accurately, population-specific benchmarks for performance outcomes must be established. OBJECTIVES To provide summary statistics for performance outcomes for Thoroughbreds racing in Hong Kong between 2000 and 2010 and to document and provide evidence on the current differences in racing careers across sexes and regions of origin for horses racing in Hong Kong. STUDY DESIGN Performance data on the population of Thoroughbreds racing in Hong Kong between 3 September 2000 and 12 March 2011 (n = 4950) were acquired and used to describe and compare the careers of Thoroughbred racehorses in Hong Kong. METHODS Career length, number of career starts and number of spells from racing per year were evaluated. Kaplan-Meier survival curves, stratified by sex, age group, country of origin and region of origin were produced for career length. A Coxs proportional hazards model was fitted to assess factors influencing the risk of retirement from racing in Hong Kong. RESULTS Log-rank tests for equality of career length survivor functions showed significant differences (P<0.001) across sexes, age groups, countries of origin and regions of origin. An increased age at first start in Hong Kong tended to increase the hazard rate for retirement from racing in Hong Kong, whereas greater earnings per race and originating from Europe tended to reduce the hazard rate for racing retirement. CONCLUSIONS AND POTENTIAL RELEVANCE Differences in career outcomes within a racing population appear to be influenced partly by the region from which a horse originates, with specific effects on each performance outcome also varying between regions. Future research should take into account these potential differences when comparing results across populations.

Multi-Species Comparative Analysis of the Equine ACE Gene Identifies a Highly Conserved Potential Transcription Factor Binding Site in Intron 16

Angiotensin converting enzyme (ACE) is essential for control of blood pressure. The human ACE gene contains an intronic Alu indel (I/D) polymorphism that has been associated with variation in serum enzyme levels, although the functional mechanism has not been identified. The polymorphism has also been associated with cardiovascular disease, type II diabetes, renal disease and elite athleticism. We have characterized the ACE gene in horses of breeds selected for differing physical abilities. The equine gene has a similar structure to that of all known mammalian ACE genes. Nine common single nucleotide polymorphisms (SNPs) discovered in pooled DNA were found to be inherited in nine haplotypes. Three of these SNPs were located in intron 16, homologous to that containing the Alu polymorphism in the human. A highly conserved 18 bp sequence, also within that intron, was identified as being a potential binding site for the transcription factors Oct-1, HFH-1 and HNF-3β, and lies within a larger area of higher than normal homology. This putative regulatory element may contribute to regulation of the documented inter-individual variation in human circulating enzyme levels, for which a functional mechanism is yet to be defined. Two equine SNPs occurred within the conserved area in intron 16, although neither of them disrupted the putative binding site. We propose a possible regulatory mechanism of the ACE gene in mammalian species which was previously unknown. This advance will allow further analysis leading to a better understanding of the mechanisms underpinning the associations seen between the human Alu polymorphism and enzyme levels, cardiovascular disease states and elite athleticism.

Handedness of whip use by Australian Jockeys

OBJECTIVE To compare handedness of whip use by Australian jockeys in Melbourne (where racing is counterclockwise) and Sydney (where racing is clockwise). METHODS Photographs of finishes of Thoroughbred horse races in Melbourne and Sydney were examined. Where whip use was clearly visible, the venue, the hand in which the whip was held and the names of the jockey and the horse were determined. Comparisons of whip hand use between cities were made using the Chi-squared test. RESULTS A total of 771 identifications were made, 328 from Melbourne and 443 from Sydney, representing 78 jockeys and 506 horses. Right-handed whip use was identified in 244 (74.39%) photographs of Melbourne races and in 313 (70.65%) photographs of Sydney races. There was no difference between right-handed whip use in Melbourne and Sydney (P = 0.53), nor in the handedness of whip use by individual jockeys (P = 0.74). Predominantly right-handed jockeys demonstrated significantly stronger dominance (84.51 ± 14.03%) compared with left-hand dominant riders (71.07 ± 9.40%; P = 0.01). A total of 84 horses were identified being ridden by the same jockey in different races. In 64 of the 84 cases, the whip was used in the same hand in all photographs. In the remaining instances, the whip was observed to be used in both hands by the one jockey. CONCLUSION The findings support the view the whip can be used as an aid to steering during races.