Relationships between racing times of Standardbreds and v^sub 4^ and v^sub 200^1

The objective of the study was to examine the validity of v^sub 4^ [velocity run under the defined conditions inducing 4 mmol/L of blood lactate concentration ([LAD])] and v^sub 200^ (velocity run under the defined conditions inducing a heart rate of 200 beats/min) to differentiate performance level among Standardbred racehorses. For this purpose, 19 Standardbred trotting racehorses with differing racing time records in 2 training yards were submitted to a standardized exercise test to determine their v^sub 4^ and v^sub 200^ (6 horses of one yard only). The test consisted of 4 or more consecutive intervals depending on when the blood [LA] of a horse increased above 4 mmol/L. Speed and time trotted, in each interval as well as time between consecutive intervals were the same for horses of a training yard. The blood [LA] measured after each interval was plotted exponentially against running speed to derive v^sub 4^ from the blood lactate-running speed relationship, and the mean heart rate during the intervals was plotted linearly against running speed to derive v^sub 200^ from the heart rate-running speed relationship. The correlation coefficient between v^sub 4^ and the racing time record was 0.77 and 0.75 for horses in racing yard A and B, respectively. There was no correlation between v^sub 200^ and the racing time record. Therefore, v^sub 4^ is a valid indicator of performance level of Standardbred trotting racehorses; however, v^sub 200^ may not be or to a lesser extent. [PUBLICATION ABSTRACT]