An investigation into progeny performance results in dual hemisphere stallions

An investigation into progeny performance results in dual hemisphere stallions Abstract The Thoroughbred has been intensely selected for speed and performance since its development over 300 years ago. The concept of shuttle stallions was introduced in 1990 in order to introduce novel bloodlines in Australia and maintain genetic diversity in the Thoroughbred population. However Thoroughbred racing varies in different racing regions with Australia requiring faster and more precocious 2 year old horses suitable for sprint races while Great Britain and Ireland has a higher demand for a horse more suited to middle distance races. The aim of this study was to test the hypothesis that environment influences progeny performance results in shuttle stallions. Thirteen stallions were identified as having shuttled between Australia and Great Britain in the 2007 and 2008 breeding seasons. This study evaluated the difference in performance among progeny of shuttle stallions that had horses racing in the Northern Hemisphere (n = 926) and Southern Hemisphere (n = 483). Overall horses in Great Britain and Ireland had a higher number of starts, wins and places than Australian progeny. They also ran in longer distance races than Australian progeny. When looked at per stallion, progeny sired by certain sires had a higher proportion of wins in Great Britain and Ireland. This study has shown that progeny performance results are influenced by the environment. Progeny of certain stallions are more likely to be suited to racing distances in Great Britain and Ireland. Stallions that are to shuttle to Australia should meet the market requirements of that country and produce progeny that are suited to that racing region. 1

Table of Contents Introduction 2 Materials and Methods 7 Results 8 Discussion 16 Conclusion 19 References 20 2

Introduction The Thoroughbred has long been valued as the most prized and high profile breed of horse in the world. The British Aristocracy in the 17 th century have been attributed with the development of the breed as a racehorse due to their enthusiasm for the sport of horse racing (Cassidy 2002). The modern day Thoroughbred horse can trace it s lineage to one of three foundation stallions; the Darley Arabian, the Godolphin Arabian and the Byerley Turk and approximately 74 foundation mares entered in the General Stud Book. Other stallions may have been responsible for the development of the Thoroughbred at the foundations stages however only three remained at the time of establishment of the General Stud Book (Cunningham, Dooley et al. 2001). The stud book was established in 1791 to preserve and maintain Thoroughbred breeding at which time the Thoroughbred became a closed population. Paternal lineages related to the Darley Arabian have been shown to be included in 95% of the population due to the popularity of his great grandson Eclipse. The Byerley Turk is accounted for through his great great grandson Herod and the Godolphin Arabian through his grandson Matchem. Thoroughbred flat racing is run over a flat track of predetermined distances. There are 5 distance groupings of races; Sprint ( 1,300 m), Mile (1,301 1,900 m), Intermediate (1,901 2,112 m), Long (2,114 2,716 m) and Extended (<2,717 m) races. Horses that compete in these races are commonly referred to as sprinters, milers or middle distance horses and stayers. Horses that are suited to sprint races are commonly found to be smaller, stockier and matured earlier than the longer distance horses. The recent discovery of the sequence variant at the MSTN gene locus has enabled prediction of the likelihood that an individual will be a sprinter (C:C), miler (C:T) or stayer (T:T) (Hill, Gu et al. 2010). The C allele has been attributed to be an indicator of speed and sprinting ability in the Thoroughbred. Thoroughbred horses have been intensely selected for their ability to excel at a particular type 3

of race with varying results depending on the continent of racing. In Australia there is a demand for a higher percentage of younger and faster sprint horses due to 37% of Group 1 races in Australia being over a distance of 1000 1400m compared to just 12% over similar distances in Great Britain. The development of racing from a long distance steeple chase race in the 1700s to a subdivision and inclusion of sprint races has led to the strong selection for speed in the Thoroughbred. This selection for speed and the incidence of sprint races has led to a varied distribution of the C allele frequency in different racing regions (Bower, McGivney et al. 2012). The selection pressures and the demand for at least one copy of the C allele has led to the distribution of C alleles in Australia being at a frequency of 0.64 while it is 0.51 in the Thoroughbred population in Great Britain (Bower, McGivney et al. 2012). The prohibition of artificial insemination in Thoroughbred breeding has led to the development of the concept of shuttling stallions between Northern and Southern hemispheres in order to gain access to novel and what may be perceived as superior bloodlines. Stallions are commonly shuttled between Australia and New Zealand in the Southern Hemisphere and Europe, North America and Japan in the Northern Hemisphere. Stallions are normally shuttled from the Northern Hemisphere in July to begin another breeding season in the Southern Hemisphere as seasons are reversed. The concept was pioneered by Arrowfield Stud, Australia in conjunction with Coolmore Stud, Ireland. While the concept was not a new one it increased in popularity from 1990 with the introduction of the Coolmore stallion Danehill. In 1990 Danehill began a shuttling career that spanned 25 consecutive seasons covering a total of 3300 mares. With his race performance and pedigree he became the first high profile shuttle stallion and was a fundamental stallion that has led to the success of the concept of dual hemisphere stallions. The influx of this pedigree into the local population has resulted in Australia s most successful stallions to date, Exceed and 4

Excel and Redoute s Choice. The shuttle stallion concept effectively doubles the book of mares that a stallion will receive and has been seen to contribute new pedigrees and bloodlines to the Australian population. To date, no significant link between inbreeding and reduction in athletic performance has been seen (Mahon and Cunningham 1982; Cothran, MacCluer et al. 1984) however it is a concern that an increase in the inbreeding coefficient and a reduction in genetic diversity may result in an increase in the incidence of diseases (Holden 1991) and in the case of Thoroughbreds, unsoundness. The introduction of shuttle stallions to Thoroughbred breeding was thought to be cause for concern in the reduction of genetic diversity (Torshizi, Nicholas et al. 1996) however it has been shown through a pedigree analysis study that between 1990 and 2005, foals in Australia that are born to one imported parent are on average less inbred than foals of Australian parentage (Castle 2007). Molecular evidence has shown that as a breed the Thoroughbred has shown increasing levels of homozygosity and increased levels of inbreeding over the last 40 years and worryingly this increase in inbreeding has been linked to the introduction of the shuttle stallion concept (Binns, Boehler et al. 2011). Heritability of best race distance has been estimated to be 0.94 and should be considered when choosing sires (Williamson and Beilharz 1998). The desirability of a stallion when choosing a sire is often influenced by earnings and previous progeny earnings. There is a breeding value of 0.33 with log of earnings as a predictor for future progeny earnings however this may be an overestimation in the case of flat racing as there are numerous training and environmental factors that will affect progeny performance (Langlois and Blouin 2004). 5

Selection for desirable traits such as sprinting ability will vary between racing regions based on the need for a particular type of horse in that region. The aim of this study was to test the hypothesis that environment influences progeny performance results in shuttle stallions. 6

Materials and Methods Using the Australian Stud Book (www.studbook.org.au), 13 stallions were identified as having consecutive breeding seasons in Australia and Great Britain/Ireland in 2007 and 2008. Three stallions covered mares in 2007 only while ten stallions covered mares in 2007 and 2008. Progeny performance data was collected for Australian horses (n = 483) from the Australian Stud Book service in coordination with Racing Information Service Australia (RISA). Progeny performance data for British and Irish horses (n = 926) was collected from the Racing Post website (www.racingpost.com). Data collected included the following variables; name of horse, sex, year of birth, total number of starts, number of wins, number of places, earnings and average distance ran. A ratio of earnings per start and percentage of winners to start was also calculated. Data analysis consisted of performing Students t-tests to compare Northern Hemisphere and Southern Hemisphere data overall, by sex, by age and by stallion. The Students t-test was also used to compare data relating to males and females within hemispheres. 7

Results Stallions were shuttled predominantly by two stud farms, Darley (n = 5) and Coolmore (n = 7) with the exception of one stallion (Tiger Hill) who was shuttled between Beechwood Grange, UK and Eliza Park Stud, Australia. Stallions had a higher number of covers in the country in which they had their race career, with the exception of Dubai Destination who had an equal number of covers in both hemispheres in the 2007 breeding season. Stallion Name Stud Farm Racing region Aus Covers 07 GB/Ire covers 07 Aus Covers 08 GB/Ire Covers 08 Tobougg Darley GB/Ire 71 136 Noverre Darley GB/Ire 35 130 Encosta de Lago Coolmore Aus 193 66 Exceed and Excel Darley Aus 183 132 148 122 Oratorio Coolmore GB/Ire 126 187 173 186 Choisir Coolmore Aus + 130 177 194 166 GB/Ire Dubai Destination Darley GB/Ire 150 149 103 141 Holy Roman Coolmore GB/Ire 131 150 180 192 Emperor Tiger Hill Darley GB/Ire 103 153 85 112 Ad Valorem Coolmore GB/Ire 84 147 82 74 Antonius Pius Coolmore GB/Ire 69 156 92 117 Aussie Rules Coolmore GB/Ire 76 141 82 136 Danbird Eliza Park Stud/ Beechwood Grange UK Aus 33 47 125 31 Table 1 exported to Great Britain in 2008 retired from stud duties no longer shuttling to Ireland 8

This study evaluated the difference in performance among progeny of shuttle stallions that had horses racing in the Northern and Southern Hemispheres. There was a significant difference between the number of starts, wins and places in Northern Hemisphere and Southern Hemisphere progeny. Horses in Australia had significantly (P = 5.54 x 10-21 ) fewer starts (4.2 starts ± 0.133) than horses in Great Britain and Ireland (6.35 ± 0.173). Horses in Great Britain and Ireland had a higher number of wins in comparison to Australian horses (P= 0.0020). AUS GB/IRL P-value (n = 483) (n = 926) Overall Start 4.26 6.35 5.54E-21 Win 0.54 0.70 0.0020 Place 0.93 1.43 3.68E-09 Distance (m) 1214.59 1562.52 2.18E-89 Table 2 Among females there was a significantly a higher number of starts (P = 2.23 x 10-11 ), wins (P = 0.007) and places (P = 0.0001) for horses racing in Great Britain and Ireland compared to females in Australia (Table 3). AUS (n = 233) GB/IRE (n = 434) P-value Females Start 4.248927039 6.33640553 2.23E-11 Win 0.454936 0.642857 0.0073 Place 0.914163 1.370968 0.0001 Table 3 9

Among males there was a significantly higher number of starts (P = 3.42 x 10-11 ) and places (P = 8.76 x 10-6 ) for horses racing in Great Britain and Ireland compared to males in Australia. There was no significant difference between wins (Table 4). AUS GB/IRE P-value (n = 250) (n = 492) Males Start 4.272 6.367886 3.42E-11 Win 0.62 0.75813 0.07867 Place 0.956 1.49187 8.76E-06 Table 4 The average distances of races competed by horses was significantly higher (P = 2.18 x 10-89 ) in Great Britain and Ireland (1562.5 m) compared to Australia (1214.6m) for all horses when grouped by age, sex and by sire (Table 5). AUS GB/IRE P-value (n = 489) (n = 926) overall 1214.596 1562.527 2.18E-89 male 1237.6 1582.114 5.47E-16 female 1189.914 1540.323 3.45E-44 2 year olds 1003.846 1385.379 4.49E-94 3 year olds 1255.185 1687.477 9.52E-81 Table 5 10

In the Australian population, males had a greater proportion of wins than females (p < 0.05). 0.8 0.7 0.6 0.5 0.4 Wins 0.3 0.2 0.1 0 Male Female Fig 1. Number of wins 11

In Great Britain and Ireland, males had a higher ratio of wins per start than females (p < 0.05) and also had a higher ratio of earnings per start than females (p < 0.05). On average, males earned 1854.52 ± 248.87 while females earned 1276.49 ± 150.69. 0.35 0.3 0.25 0.2 0.15 Wins per start 0.1 0.05 0 Males Females Fig 2. Wins per start 12

For all stallion progeny, horses that raced in Great Britain and Ireland ran significantly longer distances than Australian horses. 2000 1800 1600 1400 1200 1000 800 600 400 200 0 AUS GB/IRE Fig 3. Distance ran 13

There was a significantly higher number of starts in Great Britain and Ireland for stallions Noverre, Tobougg, Encosta de Lago, Exceed and Excel, Chosir, Dubai Destination, Holy Roman Emperor, Ad Valorem, Antonius Pius and Aussie Rules. 10 9 8 7 6 5 4 3 2 1 0 AUS GB/IRE Fig 4. Number of starts (P < 0.05) 14

There was a significantly higher number of wins in Great Britain and Ireland for progeny of Tobougg (P < 0.05), Encosta de Lago (P < 0.05), Dubai Destination (P < 0.05), Holy Roman Emperor (P < 0.01) and Aussie Rules (P < 0.05). 1.2 1 0.8 0.6 0.4 AUS GB/IRE 0.2 0 Fig 5. Number of wins (P < 0.05) 15

Discussion Danehill has been the most successful of the shuttle stallions to enter the Australian market and has topped the Leading Sires table for 9 years in Australia. Interestingly, six of the stallions included in this study are sired by Danehill and two stallions are from the same sire line as Danehill. In the 2007 breeding season there was a total of 859 stallions standing in Australia, 32 (3.75% of total stallion population) of which were stallions that shuttled between America, Europe and Japan to Australia. In 2007 shuttle stallions covered 12.6% of mares in Australia. In the 2008 breeding season there were 888 stallions standing in Australia, 44 were shuttle stallions which comprised 4.95% of the stallion population. Shuttle stallions covered 18.2% of mares in the 2008 season. Shuttle stallions have covered a large proportion of mares in the Australian population which may further impact on the reduction of genetic diversity in the Thoroughbred population. It has been reported that there has been an increased level of inbreeding in the Thoroughbred horse since 1990 (Binns, Boehler et al. 2011) which would coincide with the introduction of the shuttle stallion concept. Horses that were more successful in the northern hemisphere when looked at on a per stallion basis were sired by stallions that had raced themselves in Great Britain and Ireland. The exception to this is Encosta de Lago who sired a greater number of winners in Great Britain and Ireland than he did in Australia. Tobougg was seen to be more successful as a sire in GB/Ireland than in Australia however this may be explained by looking at the Stallion Stamina Index (SSI). The Stallion Stamina Index has been compiled by combining the average winning distance of a stallion s progeny aged 3 years old and upwards. Tobougg has a SSI distance of 1840m which would indicate that his progeny are more successful over longer distances. As stallions had a higher number of covers in the countries that they themselves had their race career this suggests that breeders of Thoroughbred horses are 16

focussed on the potential success of progeny when choosing a stallion for particular mares as they are more familiar with that stallions own race successes. In an overall view, progeny were more successful in the Northern Hemisphere, where they won more races and were placed in more races in comparison to Australian progeny. However, Australian horses earned more money overall and per start but this may be explained by the fact that Australian racing has a higher level of prize money than racing in Great Britain and Ireland. In this instance it is not applicable to use earnings as a measure of success when comparing progeny of shuttle stallions in both hemispheres. There were a higher number of starts in the northern hemisphere horses compared to Australian horses. Of the covers by shuttle stallions (n = 1384) in Australia in 2007 29% made it to the track, however in 2008 only 6.17% of the 1264 covers ran as two year olds compared to 30.06% of the progeny in Great Britain and Ireland. This may be explained by the fact that there is a higher demand for faster, precocious two year old horses in Australia and the progeny in this study may not have matured early enough to run to date. Factors such as shin soreness, tying up and foot problems have also been reported as the most common causes of two year old Thoroughbred horses in Australia not making it to the racetrack (Bailey, Rose et al. 1997). Males were more successful than females in both hemispheres which would agree with previous studies in this area (Mota, Oliveira et al. 1998; More 1999; Mota, Abrahão et al. 2005). Males may be more successful than females due to the different physiological effects experienced by both during a race. In both hemispheres, male and female horses had an equal number of starts. Horses in Great Britain and Ireland ran over distances that were longer distances than the races ran by horses in Australia. This may have contributed to the higher proportion of wins 17

and places that is seen in the progeny from Great Britain and Ireland. There is a large genetic contribution to the ability of a Thoroughbred to perform optimally at a certain race distance. The heritability of best race distance is 0.94 in the Thoroughbred (Williamson and Beilharz 1998) which indicates that horses are born suited to a particular race distance. It can be inferred from the data that progeny of Tobougg, Encosta de Lago, Dubai Destination, Holy Roman Emperor and Aussie Rules ran at a more suitable race distance in Great Britain and Ireland than the progeny of these stallions in Australia due to the higher level of wins and places. The use of a stallion that may be deemed as a long distance horse or a stayer, may not be entirely suited to the Australian market and racing region due to the fact that racing in Australia is predominately over shorter distances than in Great Britain and Ireland. Similarly horses that are more suited to sprint races will not be the main focus requirement for a European market as there is a larger proportion of middle distance and longer races in these countries. 18

Conclusion The aim of this study was to investigate whether environment has an influence on progeny performance results in dual hemisphere stallions. The success of a Thoroughbred racehorse is dependent on a number of factors from the environment and from genetics or inherited influences. This study has shown that progeny performance results in the shuttle stallions included in this cohort are influenced by the environment they are bred and produced in. Stallions that are to be shuttled to Australia should meet the market and racing requirements of that region to ensure future progeny successes. 19

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