Colostrum quality associations with passive immunity transfer in foals

Abstract

The equine epitheliochorial placentation precludes the transfer of passive immunity (TPI) from the mare to the fetus; thus colostrum serves as the sole source of TPI. Colostrum assessment at foaling with a Brix-refractometer is the primary method used in practice to determine colostrum quality and its potential for a complete TPI (>800mg/dL); however, guidelines have not been critically established. In addition, with new tools to monitor mammary gland secretions to detect impending foaling (e.g. handheld pH and conductivity devices), it would be helpful to determine if those devices can add value to the colostrum evaluation at foaling. The objectives of this study were to determine whether pH, conductivity, and Brix-index at foaling can be used to predict the TPI. One-hundred and fourteen periparturient mares had colostrum assessed at foaling for pH, conductivity, and Brix-refractometer (Laqua-Twin-Horiba, Japan). Foaling was assisted and time to stand and time to nurse were recorded. At 24h post-foaling, foals had a complete blood cell count performed, and TPI was assessed using a commercial analyzer (ARS, Foal-IgG-analyzer). Foals were grouped based on IgG concentrations as complete-TPI (i.e., ≥800 mg/dL) and failure (i.e., <800 mg/dL). Data were assessed for normality with Shapiro-Wilk's test and multiple logistic regression. The cutoff values for the Brix-index (>24.4 %), conductivity (<4.5), and pH (<6.4) were determined by ROC. The sensitivity, specificity, positive predictive value (PPP), andnegative predictive value (NPV) for the Brix-index, conductivity, and pH of the colostrum at foaling were calculated to predict the TPI. Of all foals, 74.5 % (85/114) had complete TPI, and 25.4% (29/114) failed. Foals with full-TPI had IgG (1912±278.1mg/dL) four-fold greater than those failing (480.4±260.6mg/dL P<0.0001); their Brix-indexes were 26.5±4.3 vs. 21.4±5.9 (P=0.0007), respectively. The conductivity and pH differed between complete- and failed-TPI (Conductivity 4.4±0.6 vs. 5.4±1 1.7 P=0.007, respectively; pH 6.2±0.2 vs. 6.5±0.4, P=0.02, respectively). There were strong associations between conductivity and pH (r=0.87) and a negative and strong correlation between pH, conductivity, and the Brix-index (r=-0.87; r=-0.78). The IgG was moderately correlated with RBC (r=0.70) and the Brix-index (r=0.71). Sensitivity, specificity, PPP, and NPV of the Brix-index, conductivity, and pH of colostrum at foaling to predict the TPI were 0.80, 0.76,0.95, 0.38; 0.77,0.71,0.93,0.38, and 0.75,0.37,0.71, and 0.42, respectively. TPI of Brix-index coupled with conductivity or pH presented a sensitivity, specificity, PPP, and NPV of 0.85,0.60,0.89,0.40 P=0.02, and 0.83,0.50,0.89,0.37 P=0.0.1, respectively. Combining conductivity and pH resulted in a sensitivity 0.91, specificity 0.91, PPP 0.33, and NPV 0.33. In conclusion, colostrum's Brix-index, pH, and conductivity are closely linked with TPI in foals; ROC-values could indicate if a foal could benefit from colostrum supplementation or hyperimmune plasma administration.