Prediction of metabolic acidosis in sheep with acute rumen lactic acidosis using urinary pH

This study aimed to determine whether urinary pH can be used to predict metabolic acidosis in sheep with acute rumen lactic acidosis (ALRA). ALRA was induced by administering sucrose intraruminally to 40 apparently healthy sheep. Venous blood and urine samples were collected before induction (‒18 h) and prior to treatment (0 h) to measure blood pH, base excess (BE), and urinary pH. Associations between urinary and blood pH, and between urinary pH and BE, were examined using Pearson correlation and linear regression. Blood and urinary pH were positively correlated (r = 0.633; P < 0.001), as were BE and urinary pH (r = 0.602; P < 0.001). The regression coefficients were r² = 0.401 and r² = 0.362, respectively, and the relationships were described by the following equations: pH = (urinary pH × 0.063) + 6.909; BE = (urinary pH × 3.66) ‒ 30.512. Calculated values of blood pH and BE did not differ from measured values ​​(7.346 ± 0.072 vs. 7.346 ± 0.114; P = 0.979; and ‒5.11 ± 4.21 mmol/L vs. ‒5.11 ± 6.99 mmol/L; P = 0.998, respectively). When used as a diagnostic criterion for metabolic acidosis, the BE calculated from urinary pH demonstrated a sensitivity of 81.8%, specificity of 82.5%, negative predictive value of 84.6%, positive predictive value of 79.4%, and accuracy of 82.2%. These findings indicate that urinary pH can be used as a practical predictor of metabolic acidosis in sheep with ALRA.