Objective--To test the usefulness of measuring pH and refractometry index, compared with measuring calcium carbonate concentration, of preparturient mammary gland secretions for predicting parturition in mares. Design--Evaluation study. Animals--27 pregnant Thoroughbred mares. Procedures--Preparturient mammary gland secretion samples were obtained once or twice daily 10 days prior to foaling until parturition. The samples were analyzed for calcium carbonate concentration with a water hardness kit (151 samples), pH with pH test paper (222 samples), and refractometry index with a Brix refractometer (214 samples). The sensitivity, specificity, and positive and negative predictive values for each test were calculated for evaluation of predicting parturition. Results--The PPV within 72 hours and the NPV within 24 hours for calcium carbonate concentration determination (standard value set to 400 ug/g) were 93.8% and 98.3%, respectively. The PPV within 72 hours and the NPV within 24 hours for the pH test (standard value set at 6.4) were 97.9% and 99.4%, respectively. The PPV within 72 hours and the NPV within 24 hours for the Brix test (standard value set to 20%) were 73.2% and 96.5%, respectively. Conclusions and Clinical Relevance--Results suggested that the pH test with the standard value set at a pH of 6.4 would be useful In the management of preparturient mares by predicting when mares are not ready to foal. This was accomplished with equal effectiveness of measuring calcium carbonate concentration with a water hardness kit. (J Am Vet Med Assoc 2013;242:242-248) [ABSTRACT FROM AUTHOR]