This study was carried out to calculate genetic trends on racing speed traits of Thoroughbred racehorses, using a total 208,043 racing records of 9,934 heads collected from January, 1990 to December, 2006 in Gwacheon racecourse. Repeated time, winning time and annual best time were used racing speed traits. The estimated heritabilities and repeatabilities for repeated time, winning time and annual best time were 0.288, 0.275, 0.341 and 0.502, 0.475, 0.496, respectively. Average phenotypic improvement per race year for racing speed traits were ranged from 0.115 to 0.148 second. The other side, the genetic improvement per race year for repeated time was 0.027 second but winning time and annual best time were not shown consistent trends. Therefore, we concluded that repeated time is recommended improvement trait of Thoroughbred racehorses.

The objective of this study was to estimate effects of the condition of racetrack on racing time in Thoroughbred racehorses, using 148,865 racing records for 8,189 heads that collected from KRA (Korea Racing Association). The results obtained were as follows. Based on moisture contents, the condition of racetrack was classified into Heavy, Good, Soft, Yielding and Sloppy. The condition of racetrack for last 12 years was 40.7%, 34.4%, 14.4%, 8.7% and 1.8% for Heavy, Good, Soft, Yielding and Sloppy, respectively. The frequency of heavy condition for racetrack was the highest and those of Yielding and Sloppy were relatively low. On the other hand, the frequency of heavy condition for racetrack was increased in spring and winter, whereas frequency of sloppy racetrack was increased in summer. The frequency of good condition was the highest in autumn. The regression coefficients of moisture contents in racetrack for racing time by racing distance ranged from 0.068~0.162 seconds and the racing time was faster in sloppy condition than other track conditions. The time differences between Heavy and Sloppy ranged from 1.47~3.41 seconds by distance.