Relationship between sire breeding values for the rating score on turf and dirt racing tracks in thoroughbred racehorses

Abstract

This study was conducted to determine whether there is a relationship between the rankings of sires ' breeding values, evaluated based on progeny rating scores, for turf and dirt racing tracks in Thoroughbred racehorses in Japan. Data for analysis were taken from the records of rating scores appearing in the Rating Magazine in May, 1997. Sires with at least 10 progeny having both turf and dirt rating scores were studied along with their progeny. The study populations were 116 sires and 2,754 progeny for turf racing tracks, and 116 sires and 2,797 progeny for dirt racing tracks. Sires' breeding values (EPD) were estimated with the BLUP sire model from progeny rating scores for either turf or dirt racing tracks. The fixed effects included in the BLUP sire model were sex, age of progeny and training center, whereas the sire and residuals were treated as random effects. The effect of the sire on rating scores was highly significant (P<0.001)for both kinds of racing tracks. Estimates of heritability for rating scores were 0.29 ± 0.04 at turf racing tracks and 0.18 ± 0.02 at dirt racing tracks. The correlation of a sire's EPD estimated for each kind of racing track clearly showed a positive trend, and the Spearman rank correlation was 0.502 (P≤0.001). Based on this result, we conclude that most Thoroughbred stallions produce progeny suited to both turf and dirt racing tracks.