Conductivity of mammary gland secretions is a sensitive and specific predictor of parturition in mares

Background: Accurate prediction of parturition is paramount to ensuring monitoring of delivery and preventing complications. Assessing the pH and electrolytes of the mammary gland secretions (MGS) helps detect impending parturition. As conductivity is related to electrolyte concentrations and pH, it could be a useful alternative for predicting impending parturition; however, this hypothesis warrants a critical assessment. ObjectivesTo assess the ability of conductivity, pH, and Brix in the MGS to predict parturition and to investigate their associations. Study design: Field study. Methods: The MGS of periparturient mares (n = 241) was assessed daily for conductivity, pH, and Brix index from 320d until parturition. Receiving operating curve cut-off values for conductivity (<= 4.8 mS/cm), pH (<= 6.4), and Brix index (>23.6%) were used to calculate sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for predicting parturition in <= 24 h. Results: Impending parturition was associated with a reduction in conductivity and pH (p < 0.05), and conductivity was strongly correlated with pH (r = 0.88) and Brix (r = -0.80) (p < 0.05). Sensitivity, specificity, PPV, and NPV for parturition in <= 24 h for conductivity (82%, 91%, 77%, and 92%, respectively), pH (79%, 84%, 81%, and 71%, respectively), and Brix (72%, 79%, 66%, and 83%, respectively) were determined separated and pairwise. Of interest, the sensitivity, specificity, PPV, and NPV, of combining conductivity and pH, were 80%, 95%, 90%, and 88%, respectively. Conductivity (<= 4.8 mS/cm) presented the greatest odds ratio for predicting parturition in <= 24 h, and coupling it with pH (<= 6.4 pH units) doubled its odds ratio (i.e., 25.4-62.3). Main limitations Field study. Conclusion: The conductivity of MGS is a sensitive and specific method to predict parturition. This is the first large-scale study showing that a combination of conductivity and pH is useful for predicting parturition in mares. The methods employed can likely apply to other settings with similar results.