Optimizing performance of a qualitative zinc sulfate turbidity test for passive transfer of immunoglobulin G in calves.
OBJECTIVE
To determine optimal zinc sulfate test solution concentration for detecting failure of passive transfer in calves.


METHODS
235 calves (1 to 8 days old) from a calf-rearing operation in central Washington state.


METHODS
Zinc sulfate turbidity tests, using 200-, 250-, 300-, 350-, and 400-mg/L test solutions, were performed on calf serum. These increasing concentrations were evaluated for detection of failure of passive transfer. Using 1,000 mg of IgG1/dl as the threshold for adequate passive transfer, sensitivity, specificity, and accuracy of classification were determined by comparing the zinc sulfate test results with serum IgG1 concentration (mg/dl) measured by radial immunodiffusion.


RESULTS
The 200-mg/L zinc sulfate turbidity test solution was 100% sensitive; however, specificity was only 25.5%. Increasing concentrations of zinc sulfate test solution up to 350 mg/L improved specificity with either no change or small decreases in sensitivity.


CONCLUSIONS
The endpoint of the traditional 208-mg/L zinc sulfate turbidity test for failure of passive transfer in calves is too high. Increased test solution concentrations improve specificity with only minor adverse effects on sensitivity.
Hudgens
K A
KA
Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Washington State University, Pullman 99164-6010, USA.
Tyler
J W
JW
Besser
T E
TE
Krytenberg
D S
DS
D000818:Animals; D000831:Animals, Newborn; D002417:Cattle; D005260:Female; D007112:Immunity, Maternally-Acquired; D005779:Immunodiffusion / Q000379:methods; D007074:Immunoglobulin G / Q000097:blood*; D009391:Nephelometry and Turbidimetry / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
D007074:Immunoglobulin G