THE great triviality that is horse racing is full of unanswered questions, most of which are destined to remain unanswered for as long as thoroughbreds are raced. However, today for the very first time, one such question can finally be addressed using robust statistical evidence that has never before been collected or examined.

The effect that being in-foal has on the racing performance of fillies has been the subject of discussion for decades. Every year without fail, fillies win races in the 120-day period during which they are permitted to race after becoming pregnant.