Colostrum conductivity, pH and Brix index as predictors of passive immunity transfer in foals

Foal immunity relies heavily on the absorption of colostrum immunoglobulins; thus, colostrum evaluation is used to predict the transfer of passive immunity (TPI), and its conductivity is associated with TPI in cattle. Leading up to and at parturition, a reduction in colostrum pH and conductivity is thought to be necessary for TPI; however, this remains to be determined.  The objective of this study was to assess the conductivity, pH, and Brix refractometer index of colostrum to predict the TPI in foals. The colostrum of 241 mares was assessed for conductivity, pH, and Brix index using handheld devices immediately after parturition. Twenty-hour postpartum foals had complete blood cell count and plasma IgG concentrations assessed. Foals were split into complete versus incomplete TPI (i.e., IgG ≥8 g/L vs. <8 g/L). Mare (breed, duration of pregnancy, parity, and age), foal (sex), and colostrum (conductivity, pH, and Brix index) data were computed to assess factors affecting TPI. Multivariate regression and receiver operating characteristic (ROC) curves were employed for analysis.