Comparison of two commercial radial immunodiffusion assays for detection of bovine immunoglobulin G in newborn calves.

Bovine failure of passive transfer (FPT), defined as inadequate transfer of colostral immunoglobulins from the dam to the calf, has been associated with increased risk in neonatal mortality. Currently, radial immunodiffusion (RID) assay is considered to be the gold standard in determining FPT in serum samples from calves. There are 2 commercial RID assays routinely used for serodiagnosis of FPT in calves: VET-RID and SRID. Discrepancies between results of these RID assays were observed in the authors' laboratory. The objective of this study was to compare 2 commercial RID assays by testing a paired panel of 30 blood samples collected from newborn Holsteins at birth before, and 24 hr after, ingestion of colostrum, a commercial bovine reference serum, and a panel of different concentrations of 2 purified bovine immunoglobulin G (IgG) products. Overall, the results of this study showed a high level of discrepancy and poor agreement between the 2 RID kits. The interassay precision study revealed lower between-run coefficients of variation for the VET-RID kit compared with the SRID kit. The spiking and recovery study using purified bovine IgG products demonstrated that the VET-RID kit more closely approximates the expected concentrations of the purified bovine IgG products, whereas the SRID kit consistently overestimates the concentration of purified bovine IgG products. It was concluded that this may be due to inaccuracies in the internal standards of the SRID kit.