• Study of average Thoroughbred racehorse speed on turf
• Males and geldings' speed on turf
• Females speed on turf
• Average weight carried on turf
• Study of average Thoroughbred racehorse speed on dirt
• Males and geldings speed on dirt
• Female speed on dirt
• Average weight carried on dirt
• The difference in performance between male and female Thoroughbred racehorses
• Growth of Thoroughbred racehorses

A 2015 study indicates that the peak running performance of Thoroughbred racehorses occurs at the beginning of their fourth year. The report's findings align with previous studies of horses in the United States, Brazil, and Japan.

The study focused on flat races held by the Japan Racing Association from January 1st, 2002, to December 31st, 2010. These races took place on both turf and dirt tracks with firm or standard track conditions. The racing speed of each horse was determined by dividing the race distance (in meters) by the horse's final time (in seconds). Average speeds per month for each age and distance condition were calculated for each gender group when there were 30 or more starters per month in each category.

The common change for all conditions was an average speed increase up until the first half of the age of 4 years old. The effect of increased carry weight on average speed was small, and average speed increased with the growth of the horse. After the latter half of the age of 4 years old, the horses’ average speed remained almost constant, with little variation. It is speculated that decreases in the weight carried and the retirement of less well-performing horses are responsible for the maintenance of average speed.

Study of average Thoroughbred racehorse speed on turf

The charts below show the speed of Thoroughbred horses by year and birth month at various distances.

Males and geldings' speed on turf

Male Thoroughbred horses experience a rapid increase in speed up until the beginning of their fourth year, a month or two later than female horses. After that, the speed remains fairly constant, showing a very slight improvement in speed until the age of around 8 years old.

Females speed on turf

Female Thoroughbred racehorse speed rises rapidly until the beginning of their fourth year. After that, it continues to improve slightly until around 7 years old, at which point it begins to decline slowly.

Average weight carried on turf

Study of average Thoroughbred racehorse speed on dirt

The average speed of Thoroughbred horses on dirt mimics the change in speed on turf for the most part. It may continue to improve a few months later, until around the middle of the fourth year, as the horse gains more experience on a surface that is not natural to them.

Males and geldings speed on dirt

Female speed on dirt

Average weight carried on dirt

The difference in performance between male and female Thoroughbred racehorses

The performance of male racehorses tends to exceed those of their female counterparts. However, a male horse's performance peaks quickly before leveling off, whereas a female racehorse's speed tends to peak more gradually, sometimes taking several years to reach their maximum performance.

Growth of Thoroughbred racehorses

The physiological development of Thoroughbred racehorses is thought to be completed during the latter part of the age of 4 years old. With respect to their skeletal development, the latest epiphysis closure occurs at the age of 4–5 years old in a cervical vertebra.