EXERCISE is associated with changes in acid–base status. Exercising horses often show a tendency to both metabolic acidosis, due to the accumulation of lactate, and respiratory alkalosis, as a consequence of hyperventilation. Moreover, changes in plasma water content and modification of the ionic composition of blood are also associated with exercise. Changes in acid–base status during and immediately after exercise are well documented in horses, but most studies have been carried out either in research horses and ponies performing high intensity-short time exercise on a treadmill (Parks and Manohar 1984, Forster et al 1990a, Taylor et al 1995a, Taylor et al 1995b), or during endurance rides (Rose et al 1979). To our knowledge, there are no data reporting acid–base status in horses participating in show jumping competitions. Show jumping is both an Olympic sport and a popular athletic discipline. The knowledge gained with stud- ies on acid–base status in jumpers could aid our understand- ing of the physiologic adaptations to exercise in these athletes, and help to prevent and treat disorders associated with show jumping. Interpretation of acid–base balance during exercise is complicated by the fact that many relevant variables change simultaneously and, in many instances, in opposite direc- tions. In the early 1980s, Stewart proposed a comprehensive approach to acid–base balance which is commonly known as quantitative analysis of acid–base status (Stewart 1983). Instead of focussing exclusively on the equilibrium of car- bonic acid, as traditional methods do, quantitative analysis seeks to study all the variables that influence acid–base status. This comprehensive approach requires distinction between independent and dependent variables involv acid–base balance. The independent factors responsible changes in acid–base status are: partial pressure of carb dioxide (PCO 2 ), strong ion difference (SID) and total weak acid concentrations (A T ). All the other variables commonly used for acid–base estimation (eg pH or bicarbonate dependent variables which change only when one or mo of the independent variables are modified (Stewart The quantitative approach has been reported to be usefu evaluation of acid–base balance in humans and anim both in resting and exercising individuals (Weinstein et 1991, Lindinger et al 1992, Pieschl et al 1992, Taylor et 1995a, Taylor et al 1995b, Aguilera-Tejero et al 199 Aguilera-Tejero et al 1998). Moreover, in humans, Stewa analysis has been shown to provide adequate understan of changes in the acid–base balance of venous blood dur exercise (Weinstein et al 1991). The purpose of the work reported here is to anal changes in the acid–base status of venous blood in jumpers after exercise and to evaluate the interpretation these changes using a quantitative approach. MATERIALS AND METHODS Horses Seventeen horses participating in an amateur show ju ing competition were selected. The group included geldings, seven mares and one stallion belonging to Quantitative analysis of acidÐbase balance in show jumpe before and after exercise E. AGUILERA-TEJERO, J.C. ESTEPA, I. LÓPEZ, S. BAS, R. MAYER-VALOR, M. RODRÍGUEZ* Departamento de Medicina y Cirug’a Animal, Universidad de C—rdoba, Campus Universitario de Rabana Madrid-C‡diz km. 396, 14014 C—rdoba, Spain and *Unidad de Investigaci—n, Hospital Reina Sof’a de C— SUMMARY The acid–base status of venous blood was studied in 17 show jumpers before and after exercise using both a tradition titative approach. Partial pressure of carbon dioxide (PCO 2 ), pH, haemoglobin, and plasma concentrations of sodium (Na + ), chlo- ride (Cl – ), potasium (K + ), ionized calcium (Ca 2+ ), total proteins, albumin, lactate and phosphorus were measured in jugular veno blood samples obtained before and immediately after finishing a show jumping competition. Bicarbonate, anion gap a concentration were calculated from the measured parameters. ‘Quantitative analysis’ of acid–base balance was perfor values for three independent variables: PCO 2 , strong ion difference [SID = (Na + + K + + Ca 2+ ) – (Cl – + Lact)] and total concentration of weak acids [A T = Alb (1·23 pH – 6·31) + Pi (0·309 pH – 0·469) 10/30·97]; plasma concentrations of hydrogen ion ([H + ]) were also calculated from these variables using Stewart’s equation. No significant changes in blood pH were detected after jumping competition. Exercise resulted in a significant increase in lactate, Na + , K + , haemoglobin, total proteins, albumin, globulin and anion gap, and a decrease in bicarbonate, Cl – and Ca 2+ . PCO 2 decreased after exercise while SID and A T increased. A significant correlation between measured and calculated [H + ] was found both before and after exercise. However, individual [H + ] values were not accurately predicted from Stewart’s equation. In conclusion, even though pH did not change, significant modifica acid–base balance of horses have been found after a show jumping competition. In addition, quantitative analysis has to provide an adequate interpretation of acid–base status in show jumpers before and after exercise. © 2000 Harcour 0034-5288/00/020103 + 6 $35.00/0 © 2000 Harcourt Publishers Limited Research in Veterinary Science 2000, 68, 103Ð108 doi:10.1053/rvsc.1999.0341, available online at http://www.idealibrary.com on