Estimation of Genetic Parameters for Racing Time and Ranking in Thoroughbred Horses.

Abstract

This study aimed to estimate genetic parameters for race time in seconds and final ranking, as well as to analyze the genetic trends associated with race time. The study utilized a dataset consisting of 23,290 records of race times and final ranks at distances of 1,000, 1,600, and 2,000 m from 6,213 Thoroughbred horses from the São Paulo Jockey Club. Our model considered the year of the run, animal sex, race class, track conditions, the linear effect of horse weight and age, and the quadratic effect of age as fixed covariates. Random effects included direct additive genetic, animal permanent environmental, and residual effects. Heritability estimates ranged from 0.01±0.03 to 0.17±0.04 (race time); 0.04±0.03 to 0.09±0.04 (final ranking), and repeatability from 0.19±0.02 to 0.37±0.02 (race time) and 0.15±0.02 to 0.23±0.04 (final ranking). Pearson's correlations of estimated breeding values between race time and ranking ranged from -0,027±0.16 to 0.84±0.01. When analyzing the genetic trend for races at a distance of 1,000 m, we observed a decrease in race time over time. However, for races at 1,600 and 2,000 m, a clear pattern of time reduction was not apparent. Race time offers a more promising response to selection, particularly in shorter races. Selecting for race time is expected to have a greater indirect impact on final rank. Genetic trends have revealed limited genetic progress over the years; therefore, it is advisable to reevaluate the current selection process.