TOTAL BLOOD VOLUME (TBV):
TBV varies among racehorses and is normally distributed in the racehorse population. Thus, about 60% of racehorses have average (A) or near average TBV, about 20% have below average (BA) TBV and the remaining 20% have above average (AA) TBV relative to their size. TBV is inherent to the individual and is due to differences in spleen size, and likely the amount of capillary density within the skeletal muscling of the individual. TBV increases with growth, age and intensive exercise (training) of the individual, and is greater in intact males compared to females and gelded males due to the additional muscle mass these individuals naturally possess. TBV is related to body size, but can still vary more than 10% in individuals of the same size, age and gender. Consequently, given two yearlings of the same size, age, and gender, one could possess as much as 3 additional liters of blood, which may be of interest to sellers making marketing decisions, a s well as most potential buyers.