Total blood volume and thoroughbred racing performance

Total blood volume (TBV) was measured on 47 mature race-retired Thoroughbreds and compared with individual performance records. TBV had a near normal distribution with a mean of 49.2 ± 5.0 L. Thirty-three of the 47 horses (70.2%) were stakes horses (SH). There was a difference (P < .01) in the percentage of SH with below average (BA) TBV (36.4%) compared with the percentage of SH with average (A) TBV (73.1%) and an even greater difference (P < .001) when compared with horses with above average (AA) TBV (100%). Further, there was a difference (P < .001) in the percentage of graded stakes horses (GSH) with BA-TBV (0%) compared with those with A-TBV (23.1%) and AA-TBV (30%). TBV was related (P < .05) to overall performance level (r = 0.45). There was no difference in the average earnings per start (AEI) of horses with BA- and A-TBV; however, horses with AA-TBV had a higher (P < .05) AEI, and overall TBV was related to AEI (r = 0.34). TBV is a measure of oxygen delivery capacity, and since it is inherent to the individual, values from yearlings and unraced 2-year-olds should provide buyers with an objective, performance-related physiologic parameter to use in selection.