Heritability and repeatability of speed for 2- and 3-year-old standardbred racehorses.

The research article is about a study measuring the heritability and repeatability of racing time in 2- and 3-year old Standardbred racehorses to determine if it is a valid selection criterion.

Research Overview

• The article describes a study conducted on 7,206 2- and 3-year-old Standardbred pacers and trotters. The horses competed in 1-mile races at six different tracks from 1975 to 1978.
• A total of 38,487 records representing 2,387 sire progeny groups were analyzed. The records were divided into subsets according to gait, age and track.

Methodology and Findings

• Initially, the researchers recognized “class of race” as a subjective parameter which represented the nonrandom assignment of horses to races. However, after extensive investigation, they found it necessary to adjust the race times by linear regression using the time of the winning horse (the “pace” of the race).
• Regression coefficients of time on the pace ranged from .61 to .79 and were found to adequately account for the environmental effects of class.
• Heritability of racing time (the degree to which racing time can be inherited from parent to offspring) ranged from -0.25 to 0.66, while repeatability (consistency of racing time in the same horse) ranged from 0.32 to 0.55.

Overall Findings and Conclusion

• The overall estimates of repeatability and heritability were 0.44 and 0.29 respectively. However, when data were not adjusted for pace, these estimates were inflated due to environmental effects.
• The researchers concluded that racing time adjusted for pace is a valid and useful selection criterion for Standardbred horses.