Comparison of refractometers and test endpoints in the measurement of serum protein concentration to assess passive transfer status in calves.
OBJECTIVE
To evaluate 3 refractometers for detection of failure of passive transfer (FPT) of immunity in calves, and assess the effect of refractometric test endpoints on sensitivity, specificity, and proportion of calves classified correctly with regard to passive transfer status.


METHODS
Prospective study.


METHODS
90 calves.


METHODS
Blood samples were obtained from calves that were < 10 days old. Serum IgG concentration was determined by use of a radial immunodiffusion assay. Accuracy of 3 refractometers in the prediction of serum IgG concentration was determined by use of standard epidemiologic methods and a linear regression model.


RESULTS
At a serum protein concentration test endpoint of 5.2 g/dL, sensitivity of each refractometer was 0.89 or 0.93, and specificity ranged from 0.80 to 0.91. For all refractometers, serum protein concentration test endpoints of 5.0 or 5.2 g/dL resulted in sensitivity > 0.80, specificity > 0.80, and proportion of calves classified correctly > 0.85. Serum protein concentrations equivalent to 1,000 mg of IgG/dL of serum were 4.9, 4.8, and 5.1 g/dL for the 3 refractometers.


CONCLUSIONS
The refractometers, including a nontemperature-compensating instrument, performed similarly in detection of FPT. Serum protein concentration test endpoints of 5.0 and 5.2 g/dL yielded accurate results in the assessment of adequacy of passive transfer; lower or higher test endpoints misclassified larger numbers of calves.
Calloway
Christopher D
CD
Department of Veterinary Medicine and Surgery, College of Veterinary Medicine, University of Missouri, Columbia, MO 65211, USA.
Tyler
Jeff W
JW
Tessman
Ronald K
RK
Hostetler
Douglas
D
Holle
Julie
J
D000818:Animals; D000831:Animals, Newborn; D001798:Blood Proteins / Q000032:analysis; D002417:Cattle / Q000097:blood* / Q000276:immunology; D005260:Female; D007112:Immunity, Maternally-Acquired; D005779:Immunodiffusion / Q000662:veterinary; D007074:Immunoglobulin G / Q000097:blood*; D011446:Prospective Studies; D012031:Refractometry / Q000295:instrumentation / Q000379:methods / Q000662:veterinary*; D012044:Regression Analysis; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
D001798:Blood Proteins; D007074:Immunoglobulin G