Evaluation of passive immunity transfer in Danish dairy calves measured by enzyme-linked immunosorbent assay and Brix refractometer

Calves are born agammaglobulinemic and depend on transfer of passive immunity from colostrum. Failure of transfer of passive immunity (FTPI) and adequate transfer of passive immunity (ATPI) are defined as serum immunoglobulin G (IgG) levels < 10 and ≥ 10 mg/mL, respectively. The objective of this study was to evaluate the level of passively transferred immunity in Danish dairy calves measured with Enzyme-linked immunosorbent assay (ELISA) and Brix refractometer. Blood samples from 834 calves (430 bull calves and 404 heifer calves) aged two to nine days were included in the study. Serum IgG concentration was determined by ELISA and percentage Brix (%Brix) with a digital refractometer. Median serum IgG concentration was 17.05 mg/mL and mean %Brix was 8.5%. A total of 592 (71.0%) and 242 samples (29.0%) had a serum IgG concentration ≥ 10 mg/mL and < 10 mg/mL, respectively. For %Brix 541 (64.9%) and 293 (35.1%) was ≥ 8.1 and < 8.1%, respectively. Serum IgG concentrations and %Brix measurements were highly correlated (r = 0.88). The level of passive immunity in Danish dairy calves seems low and does not meet new recommendations. However, applying cut-offs based on radial immunodiffusion to serum IgG concentrations derived from ELISA are not straightforward and determination of new cut-off values for FTPI based on ELISA are recommended.