CASE STUDY: Using Urine pH as a Predictor for Ketosis in Transition Dairy Cows1

An experiment was conducted to determine whether urine pH could be used to predict the incidence of ketosis in transition dairy cows. Urine was collected three times weekly from 41 Holstein cows from approximately 21 d prepartum until 21 d postpartum. Concentrations of acetoacetate and the pH of the urine were measured immediately; then, the urine was stored frozen until later analysis for concentrations of β-hydroxybutyrate (BHBA). Correlations between urine pH and concentrations of acetoacetate and BHBA were −0.50 and −0.65, respectively. Stepwise regression was used to determine variables that were related to concentrations of ketones in the urine. Urine pH was a significant (P<0.05) predictor for both acetoacetate and BHBA concentrations in urine. Additional predictor variables for acetoacetate concentrations were somatic cell count score (SCCS), DMI, milk protein yield, day relative to calving, and calving date. Additional predictor variables for BHBA concentrations were SCCS, DMI, milk protein percentage, milk fat yield, day relative to calving, calving date, and animal identification. Inclusion of the cow-specific variables calving date, day relative to calving, and animal identification as significant predictors is an indication that urine pH is not a good predictor of ketosis status across an entire herd but may be useful for specific cows with a known history.