Faculty of Veterinary Science, University of Sydney, Sydney, New South Wales, Australia.
Equine Vet J. 2013 Jul;45(4):410-3. doi: 10.1111/j.2042-3306.2012.00651.x. Epub 2012 Sep 26.
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.
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.
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.
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.
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.
对纯种赛马种群的研究表明，对于 2 岁开始比赛的马，其赛马生涯有积极的影响。目前，针对澳大利亚纯种赛马种群中是否存在这种影响的研究有限。
调查澳大利亚纯种马种群中首次参赛年龄与赛马生涯长度之间的关系，并根据首次参赛年龄、职业生涯收入、2 岁时的参赛次数和参赛距离，估计澳大利亚赛马退役的风险。
收集了 1998 年 1 月 1 日或之后出生、2000 年 8 月 1 日至 2011 年 2 月 22 日期间在澳大利亚参赛的纯种马数据。按年龄组制作了职业生涯长度的 Kaplan-Meier 生存曲线。拟合 Cox 比例风险模型评估影响赛马退役风险的因素。该模型包括性别、首次参赛年龄、职业生涯收入、2 岁时的参赛次数、参赛距离和适当的交互项。
研究人群包括 117088 匹马。骟马的职业生涯明显长于母马和公马（P<0.001），母马的职业生涯明显长于公马（P<0.001）。首次参赛年龄越小、2 岁时的参赛次数越多、平均参赛距离越长，赛马退役的风险越低。对于公马，随着收入的增加，赛马退役的风险增加，而对于母马和骟马，随着收入的增加，赛马退役的风险降低。
向澳大利亚的年轻纯种马引入赛马似乎对这些马没有明显的不良影响。与退役相关的一些风险因素的影响因性别而异，在评估职业表现时应予以考虑。
