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

Abstract

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 11d of age. Serum IgG concentration was determined by radial immunodiffusion (RID) assay. The mean IgG concentration was 1,764±1,035mg/dL, with a range from 133 to 5,995mg/dL. The ZAPvet Bovine IgG test was used to assess FTPI (serum IgG <1,000mg/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.

Evaluation of 5 methods for diagnosing failure of passive transfer in 160 Holstein calves

“…For Passing‐Bablok regression, the intercept value reflects constant bias, and the slope reflects proportional bias . Agreement was also examined using the Bland‐Altman difference plots assessing the difference in the measured values by the 2 methods ( y ‐axis) against the mean of the measured values ( x ‐axis) . The upper and lower limits of agreement for the Bland‐Altman difference plots were calculated from the bias ± 1.96 × SD; the bias estimate reflects the mean bias over the range of measured values and therefore includes both the constant and proportional biases identified using Passing‐Bablok regression.…”

“…41 Agreement was also examined using the Bland-Altman difference plots assessing the difference in the measured values by the 2 methods (y-axis) against the mean of the measured values (x-axis). 42 The upper and lower limits of agreement for the Bland-Altman difference plots were calculated from the bias AE 1.96 9 SD; the bias estimate reflects the mean bias over the range of measured values and therefore includes both the constant and proportional biases identified using Passing-Bablok regression. Acceptable agreement between the 2 methods for determining STP concentration (95% limits of agreement) was designated as À3 to 3 g/L, based on the range of published values for FTPI cut points (52-55 g/L).…”

Short communication: Validation of methods for practically evaluating failed passive transfer of immunity in calves arriving at a veal facility

“…If the ZAPvet test line was lighter in color than the referent line, the calf was considered to have FPT. However, if the test line was similar or darker in color than the referent line, the calf was considered to have successful passive transfer of immunity (Elsohaby and Keefe, 2015). The vacuum tube blood samples were allowed to clot and then were centrifuged at 1,500 × g for 15 min at approximately 20°C.…”

“…Serum total protein (STP) determined by refractometry has been shown to be well correlated with immunoglobulin concentrations measured by RID in dairy calves (Naylor and Kronfeld, 1977), but it has not been validated in calves upon arrival at veal facilities, where the age of the calves is unknown and many calves are dehydrated (Renaud et al, 2018). A new semiquantitative antibody test (ZAP test) has been validated using serum from dairy calves; however, it has not been used on whole blood (Elsohaby and Keefe, 2015). Utilizing this test on whole blood may allow for a quicker point-of-care decision and reduce the amount of time required to determine passive transfer of immunity status.…”

“…Despite showing efficacy when assessing FPT on serum (Elsohaby and Keefe, 2015), the semiquantitative IgG test used on whole blood was not valuable in identifying veal calves with FPT. The test had moderate sensitivity, but the low specificity would lead to a large number of false positives.…”