A parallel evaluation of 5 indirect cost-effective methods for assessing failure of passive immunity transfer in neonatal calves.

The aim of this study was to evaluate the diagnostic accuracy of 5 indirect methods that may be used in veterinary practices to assess the success of maternal immunoglobulins transfer in neonatal calves. Blood samples (n = 245) were collected from 2- to 6-d-old calves. Serum immunoglobulin concentrations were determined by radial immunodiffusion. Serum total protein and albumin concentrations and γ-glutamyl transferase activity were determined by veterinary practitioners using their own biochemistry analyzer. Globulin concentration was calculated. Veterinary practitioners were also asked to assess serum total protein using a digital Brix refractometer (%Brix) and an optical refractometer (g/L). Test sensitivity (Se) and specificity (Sp) were calculated using radial immunodiffusion as the reference standard, with failure of transfer of passive immunity defined as IgG <10.0 g/L. Receiver operating characteristics curves were created and optimal cutoff values for each of the 5 indirect measurement methods were selected based on the maximization of the Youden's statistic. In this study, Globulin concentration yielded the highest accuracy to identify failure of transfer of passive immunity (Se = 89.4%; Sp = 89.3% at 34 g/L). For %Brix, the optimal combination of Se and Sp was at 8.4% Brix (Se = 86.5% and Sp = 83.8%). The use of an optical refractometer was associated with the lowest diagnostic accuracy (Se = 69.7% and Sp = 81.6% at 52 g/L). For γ-glutamyl transferase activity, the optimal cut-points were different for 2- to 3-d-old calves (Se = 87.5% and Sp = 87.8% at 393 IU/L) or 4- to 6-d-old calves (Se = 90.0% and Sp = 86.4% at 254 IU/L). Because it does not require any specialized laboratory equipment, digital Brix refractometer can be a valuable and inexpensive tool for on-farm use, to help producers and veterinary practitioners in their calf health management programs.