Prerace venous blood acid-base values in standardbred horses

The administration of sodium bicarbonate (NaHCO3) or 'milk shakes' to Standardbred horses before racing is widespread. This study analysed nonrace day (CTL) and prerace venous acid-base values from Standardbred horses racing in Pennsylvania (PA) and New Jersey (NJ). Mean +/- s.d. CTL bicarbonate (HCO3) and base excess (BE) values, for a group of horses stabled during the 1993 racing season at Pocono Downs, Pennsylvania, were 28.6 +/- 1.9 and 2.6 +/- 1.7 mmol/l, respectively. In the same population of horses, mean +/- s.d. values for prerace HCO3- and BE values were 33.1 +/- 2.8 and 7.0 +/- 2.3 mmol/l, respectively, for horses administered frusemide (F) 4 h before race time and 31.5 +/- 2.4 and 5.5 +/- 2.0 mmol/l for the horses not administered frusemide (NF). There were differences (P < 0.05) in pHv, PvCO2, HCO3- and BE values between the CTL and prerace samples. The venous acid-base values of the CTL horses were normally distributed. The prerace acid-base values measured during 1993 were not normally distributed, indicating changes due either to the administration of alkalising substances or other manipulations of the horses on race day. Changes in all acid-base values were observed during the subsequent 1994 racing season with further changes observed when horses were placed in a secured stable 8 h before the race. The criteria used in some racing jurisdictions for disqualifying a horse were the elevations in HCO3-, Na+ and pH. The correlation coefficients (r2) for the least squares regression for HCO3- vs. pH and HCO3- vs. Na+ in prerace venous blood samples were 0.31 and 0.21, respectively, indicating a poor relationship between the 3 acid-base values. To discourage the administration of NaHCO3 to horses before a race, the use of a BE value of > or = 10 mmol/l for NF and > or = 12 mmol/l for F was adopted as a single index for the disqualification of horses from a race. The results of this study indicate that the use of a single index and, in this case BE, has curtailed the prerace administration of NaHCO3 to horses.