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The association of age at first start with career length in the A ustralian T horoughbred racehorse population
Author(s) -
Velie B. D.,
Knight P. K.,
Thomson P. C.,
Wade C. M.,
Hamilton N. A.
Publication year - 2013
Publication title -
equine veterinary journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.82
H-Index - 87
eISSN - 2042-3306
pISSN - 0425-1644
DOI - 10.1111/j.2042-3306.2012.00651.x
Subject(s) - earnings , demography , population , hazard ratio , proportional hazards model , medicine , economics , confidence interval , finance , sociology
Summary Reasons for performing study Studies of T horoughbred 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 A ustralian T horoughbred racing population is limited. Objectives To investigate the association between age at first start and career length in the A ustralian T horoughbred population and estimate the risk of racing retirement for horses racing in A ustralia based on age at first start, career earnings, number of starts as a 2‐year‐old and distance raced. Methods Data were collected for T horoughbreds, born on or after 1 J anuary 1998, that had raced between 1 A ugust 2000 and 22 F ebruary 2011 in A ustralia. A K aplan– M eier survival curve, stratified by age group, was produced for career length. A C ox 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 T horoughbreds to racing appears to have no apparent adverse effects on these horses racing in A ustralia. The impact of some risk factors associated with retirement from racing varied between sexes and should be considered when evaluating career outcomes.