Estimation of genetic trend in racing performance of thoroughbred horses.

The research investigates whether the genetic trend among thoroughbred racehorses might explain why winning race times have not improved recently despite strong selective breeding practices. The study concludes that insufficient genetic variance in the thoroughbred population is not the cause of this stagnation.

Introduction

• The authors begin by discussing the early history and practice of thoroughbred horse breeding, tracing its origin largely to horses imported from the Middle East and North Africa to England in the late seventeenth and early eighteenth centuries.
• They explain that over 80% of the gene pool of the thoroughbred population comes from 31 original ancestors recorded in the Stud Book, established in 1791, after which the thoroughbred population became isolated from outside gene sources.

The Research Problem

• Despite extensive selective breeding practices, particularly on the male side, and the high inheritability of various measures of racing performance, race winning times have not improved in recent decades.
• This led the researchers to hypothesize that perhaps the additive genetic variance in performance might have been exhausted due to the intense breeding selection.

The Research Method

• To test this hypothesis, the authors estimated the genetic trend in racing performance over the period of 1952-1977 using TIMEFORM handicap ratings.
• These ratings provide a weight, measured in pounds, expressing the horse’s racing merit based on its performance in an average free-handicap race.
• The rating considers many factors, such as the firmness of the ground, the distance of the race, and the level of competitors.

Results and Conclusion

• The authors found that the lack of improvement in racing times is not due to a lack of genetic variance in the thoroughbred population.
• This indicates that there may be other barriers to improvement in racing performance, beyond the genetic potential of the horses.