An Australian study of 117,088 thoroughbreds found that those raced regularly as two-years-olds were more likely to have longer careers.
Researchers from the Faculty of Veterinary Science at the University of Sydney and the Sydney Medical School said overseas thoroughbred studies had provided evidence of a positive effect on racing careers for horses that started racing as two-year-olds, but research in the area was limited in Australia.
They set out to investigate the association between the age at first start and career length, and to estimate the risk of racing retirement for horses racing in Australia based on age at first start, career earnings, the number of starts as a two-year-old, and distance raced.
The researchers, whose findings have been published in the Equine Veterinary Journal, found no evidence of adverse effects in starting thoroughbreds at two-year-olds.
The researchers collected data for Australian thoroughbreds born on or after January 1, 1998, that had raced between August 1, 2000, and February 22, 2011.
The study population included 117,088 horses.
They found that geldings had significantly longer careers than mares and stallions, and mares had significantly longer careers than stallions.
The risk of retirement from racing decreased with a younger age at first start, a higher number of starts as a two-year-old, and a longer average distance raced.
For stallions, the risk of retirement from racing increased as earnings increased, while for mares 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 authors concluded.
“The impact of some risk factors associated with retirement from racing varied between sexes and should be considered when evaluating career outcomes,” they noted.
New Zealand research exploring a similar question was published last year in the Equine Veterinary Journal.
Velie, B. D., Knight, P. K., Thomson, P. C., Wade, C. M. and Hamilton, N. A. (2013), The association of age at first start with career length in the Australian Thoroughbred racehorse population. Equine Veterinary Journal, 45: 410–413. doi: 10.1111/j.2042-3306.2012.00651.x
The abstract can be found here.