Evaluation of Optical Refractometer for Assessing Failure of Transfer of Passive Immunity in Foals

The aim of the present study is to evaluate the correlation between the total protein measured by an optical refractometer and the concentration of IgG by radial immunodiffusion (RID) to determine the performance of the optical refractometer to diagnose the failure of passive transfer of immunity (FPTI) in 12-hour-old foals. Blood was collected from foals (n = 30) 12 hours after birth. A study was carried out to measure the serum IgG concentration by RID test and measure total protein (TP) by optical refractometer. The correlation coefficient was measured between the TP concentration and the IgG-RID. Correlation was made between the IgG-IDR levels of colostrum in mares and the IgG-IDR concentration of the plasma of the foals. A ROC curve was made to identify the ideal cutoff point, in addition to the tests for sensitivity and specificity. The area under the curve (AUC) was calculated. The IgG concentration by RID was positively correlated with a refractometer. Colostrum IgG concentration by RID was moderately correlated with foal plasma IgG-RID concentration. In the ROC curve, AUC was 0.931, and the cutoff point found was ≤5,7 g/dL as the most optimal combination, with 100% sensitivity and 73.3% specificity. Thus, it can be concluded that the total protein concentration by refractometer shows effective utility in the evaluation of FPTI in foals since they are highly sensitive, associated with a low cost, easy to handle, and easily carried out in the field.