Mammary gland secretions’ conductivity alone or coupled with pH as a novel and accurate predictor of foaling and its association with electrolytes

Abstract

Accurate prediction of parturition is paramount to providing assisted delivery and preventing foaling-induced complications. Assessment of pH and electrolyte concentrations of mammary gland secretions (MGS) are useful to detect impending parturition. The study's hypothesis was that changes in electrolytes and pH alter the conductivity of MGS, thus conductivity could be a more accurate foaling predictor than pH and electrolytes alone. In experiment 1, periparturient mares (n=23) had MGS assessed daily for pH, conductivity, and electrolytes (Ca2+, Na+, and K+) using bench-top analyzers (LAQUA-Twin D 771, Horiba LTDA, Kyoto Japan for pH and conductivity; and Hitachi 911 Roche Diagnostics, Basel Switzerland for electrolytes) and portable handheld devices. Handheld devices (LAQUA-Twin, Horiba) were also compared with bench top analyzers. Mixed-model analyses revealed significant reductions in pH, conductivity, Na+, and increases in Ca2+, and K+ upon impending parturition. Bland-Altman analyses showed no significant deviation from linearity for all devices. In experiment 2, periparturient mares (n=114) had daily MGS assessed for conductivity, pH, and electrolytes using hand-held devices (Laqua-Twin).Mixed-model analyses showed effects of time (P<0.05), but no effect of group (P>0.05) or interaction (group*time) (P>0.05) for all analytes. Conductivity was strongly associated with pH (r=0.90), and moderately associated with Na+ (r=0.77), Ca2+ (r= -0.60), and K+ (r= -0.70). Analyses of receiver operating characteristic (ROC) were performed to determine the cut offs for foaling in 24 h for all analytes; and then the cut off values were used to calculate the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV). The results were: conductivity for sensitivity, specificity, PPV, and NPV (0.82, 0.80, 0.82, and 0.60), pH (0.80,0.78,0.81, and 0.70), Ca2+(0.92,0.35,0.68, and 0.76), Na+ (0.65,0.28,0.53, and 0.39), and K+ (0.67,0.25,0.50,0.41). The sensitivity, specificity, PPV, and NPV, for conductivity coupled with pH, were 0.84,0.85, 0.81, and 0.90 respectively. In conclusion, the handheld devices tested herein are as accurate as bench-top analyzers for pH, conductivity, and electrolytes. The conductivity of MGS showed similar results to pH to predict of foaling, and the combination of pH and conductivity enhanced the prediction of parturition in mares.