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¹ Department of Livestock, Dalaman Agricultural Enterprise, General Directorate of Agr. Enterprises, Muğla, Türkiye
² Department of Animal Sciences, Faculty of Veterinary Medicine, Ankara University, Ankara, Türkiye DOI : 10.46897/livestockstudies 1222935 - This study was aimed at determining and comparing the diagnostic accuracy of digital and optical Brix refractometers (D-Brix and O-Brix, respectively) for the estimation of passive immunity status (<16 and <24g/L) in beef calves. Blood was sampled from 163 one to sevenday- old calves. Immunoglobulin G (IgG) concentrations were estimated with D-Brix and O-Brix refractometers, and measured by the radial immunodiffusion (RID) assay used as the reference test. Correlation coefficients (r) were calculated for the results of each method. Youden`s Jindex was used to select optimal refractometer cut-off values for estimating IgG of <16 and <24 g/L. Overall test performance and refractometer agreement were assessed using AUCs, diagnostic test accuracy, Cohen's kappa coefficient (κ), and Bland-Altman analysis. Positive correlations existed between the RID-IgG concentrations and Brix percentages (r=0.903 for DBrix, r=0.885 for O-Brix), and between the results of the two refractometers (r=0.992). The overall test performances of the refractometers were excellent (AUC>0.90). For predicting serum IgG concentrations of <16 and <24 g/L, the optimal cut-off values were ≤8.3% and ≤9.4% for the D-Brix refractometer, and ≤8.4% and ≤9.6% for the O-Brix refractometer, respectively. At the optimal thresholds for estimating serum IgG concentrations of <16 g/L, the sensitivity and specificity were 91.89% and 97.62% for the D-Brix refractometer, and 91.89% and 96.83% for the O-Brix refractometer, respectively. At the optimal thresholds for estimating serum IgG concentrations of <24 g/L, the sensitivity and specificity were 88.14% and 80.77% for the DBrix refractometer, and 86.44% and 80.77% for the O-Brix refractometer, respectively. Cohen`s kappa coefficients suggested an almost perfect agreement between the results of the two refractometers for the estimation of IgG of <16 (κ=0.90) and <24 g/L (κ=0.86). In conclusion, digital and optical Brix refractometers could be safely used as monitoring tools for assessing passive immunity status in neonatal beef calves. Keywords : Beef calf Brix Optic Digital Passive immunity