Preliminary validation of a calf-side test for diagnosis of failure of transfer of passive immunity in dairy calves

The objective of this study was to evaluate the utility of an initial version of a calf-side test (ZAPvet Bovine IgG test, ZBx Corp., Toronto, ON, Canada) for diagnosis of failure of transfer of passive immunity (FTPI) in dairy calves. Blood samples (n = 202) were collected from calves from 1 to 11 d of age. Serum IgG concentration was determined by radial immunodiffusion (RID) assay. The mean IgG concentration was 1,764 ± 1,035 mg/dL, with a range from 133 to 5,995 mg/dL. The ZAPvet Bovine IgG test was used to assess FTPI (serum IgG <1,000 mg/dL) and test characteristics were calculated. The number of samples that had FTPI from the RID assay and ZAPvet test was 55 and 96 samples, resulting in a true prevalence of 27% and an apparent prevalence of 47.5%, respectively. The sensitivity, specificity, and positive and negative predictive values of the ZAPvet test were 0.82, 0.65, 0.47, and 0.91, respectively. The results of the ZAPvet test were derived from 2 observers, and the overall level of agreement between the results of the 2 observers was 84%, with a kappa value of 0.67. The ZAPvet Bovine IgG test showed good potential for further development as a cost-effective, rapid calf-side test for monitoring FTPI in dairy calves.