Comparison of Different Methods to Determine the Absorption of Colostral IgG in Newborn Foals

The timely diagnosis of abnormalities in the passive transfer of colostral immunoglobulins is important for the health and development of newborn foals. This study investigated three different methods for measuring immunoglobulin G concentration in neonatal foals. Comparison of a commercial SNAP assay, total protein concentration determination, and total globulin calculation by subtracting the albumin fraction from total protein as an indirect parameter was performed on a quantitative ELISA, which served as a reference method. The study included 119 samples from 148 foals between the age of 1 and 6 days. A blood concentration of 800 mg/dL was considered to indicate adequate absorption of immunoglobulins, and a concentration of less than 400 mg/dL was considered to be hypogammaglobulinemia. The sensitivity of the SNAP test was 64.5% and specificity was 94.7% for diagnosing sufficient absorption of immunoglobulin G at a value of 800 mg/dL. A value of 54 g/L was found to be most appropriate for the use of total protein and provided a sensitivity of 67.3% and specificity of 84.2%. For total globulins, the most appropriate value was 27 g/L, which yielded a sensitivity of 74.5% and specificity of 81.6%. At values under 400 mg/dL, the sensitivity of the SNAP test was 89.4% and the specificity was 83.0%. Here, the most suitable value for the total protein was 51 g/L. This provides a sensitivity of 65.2% and a specificity of 76.8%. The most suitable concentration for the use of total globulin was determined to be 24 g/L, which provided a sensitivity of 75.8% and a specificity of 78.1%. The study and its results show that the SNAP test, the TP, and the TP-A method perform similarly well compared to the ELISA in determining IgG concentration of ≥800 mg/dL. Based on the 95% confidence intervals, however, the Snap test and the TP-A method appear to perform similarly well but better than the TP approach for IgG concentrations <400 mg/dL.