In recent months Brandon Velie, a PhD student at Sydney University has published three very interesting population studies on horses in Australia and Hong Kong in the Equine Veterinary Journal.
Brandon's particular interest is durability of the breed on a population basis (tens of thousands of horses) and his studies have thrown up some interesting facts (my comments in brackets).
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. (This is a very similar finding to other studies on the breed. Basically saying that you should not race a horse at two is counter to what is best for the horse. The more they race at two, the sounder they are as older horses. By owners/trainers delaying the first start of a horse they are more likely to just delay whatever muscoskeletal issue they have until they are three and effectively shorten their whole career).
In Hong Kong, differences in career outcomes within a racing population appear to be partially influenced by the region from which a horse originates. (Horses that are bought in from Europe seem to last longer in Hong Kong than those brought in from other countries. Some countries are producing less sound horses than others)
In Australia, geldings had significantly longer careers than females and intact males (no surprise there)
Females had significantly longer careers than intact males. (that is a little surprising as I would have thought mares would be retired to stud at the same rate as stallions)
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 (that makes sense in that once a horse wins a big G1 race it is only a matter of time before he is retired as a stallion whereas mares that are earning and racing well stay in training)