University of Sydney researchers have addressed this issue in the most comprehensive study yet undertaken to determine whether the age at which thoroughbreds start their career has an effect on the length of their career.
They found no detrimental effect on a horse's career if it started racing as a two-year-old, and that thoroughbred horses beginning their careers in Australia at younger ages were more likely to have longer careers than those starting their careers later in life.
"This is the largest and most extensive study of its type as we investigated the careers of over 115,000 Australian thoroughbred racehorses and evaluated them throughout a 10 year period," said Natasha Hamilton, the supervising author at the University's Faculty of Veterinary Science. Dr Hamilton is co-supervisor of PhD candidate Brandon Velie, lead author of the study published in the Equine Veterinary Journal.
The study also used the horse's exact age at each race as defined by its birth date, rather than simply by year of birth, making it more accurate than comparable studies.
"The survival analysis showed the risk of retirement from racing decreased the younger the horse was when it ran its first race," Dr Hamilton said.
Risk of retirement also decreased with the number of starts a two-year-old had, and with average distance raced.
"Our study supports earlier findings but is based on a much larger sample," said Dr Hamilton, who alongside her university career has worked as a race day official for more than 15 years.
Overall, the research suggests that the racing and training of two-year-old thoroughbreds is not harmful as long as there is an awareness that combining an inappropriate training regime with a genetic predisposition to injuries can result in injuries that prevent the horse from continuing or beginning its racing career.
"We still advise caution when introducing young horses to racing," Dr Hamilton said.
"It is important to note that this study is not able to claim causation and does not mean that any thoroughbred horse can be raced at two. Instead we observed that for those thoroughbreds that have started racing at two no ill effect can be detected."