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

BackgroundInadequate absorption of colostral IgG1is termed failure of transfer of passive immunity (FTPI). Dairy calves withFTPIhave increased mortality and morbidity in their first 6 months of life.ObjectivesThis study compared the clinical performance of 5 methods for diagnosingFTPIin Holstein calves.MethodsAn observational study was performed using 160 Holstein heifer calves. Serum was harvested at 48 hours of age, andFTPIwas assessed using a digital Brix refractometer for total solids measurements, and digital refractometry and the biuret method to measure serum total protein (STP) concentrations. Serum gamma‐glutamyltransferase activity was measured with an automated analyzer, and serum IgG was measured with the zinc sulfate turbidity test and an enzyme‐linked immunosorbent assay. Diagnostic test performance was compared with that of the reference method (FTPIdefined as a serum total IgG concentration <10 g/L). Test performance was evaluated using the area under the receiver operating characteristic curve, the sensitivity, the specificity, and the positive likelihood ratio at the optimal test cut point, and by calculating the kappa coefficient.ResultsA serum digital Brix percentage of <7.8% and anSTPconcentration of <52 g/L measured using digital refractometry were the best methods to identify calves withFTPI. TheSTPconcentration measured with digital refractometry was 0.1 g/L lower than that measured with the biuret method.ConclusionsThe digital Brix refractometer and the digital refractometer provide accurate and clinically useful methods for identifying dairy calves withFTPI. In this study, the excellent performance of the Brix refractometer was likely due to the use of a fixed sample volume (200 μL) and a uniform sample temperature at the time of measurement.