Diagnostic accuracy of digital Brix and serum total protein refractometers in estimating different passive immunity levels in dairy calves

Changes in serum total protein and immunoglobulin G concentrations and Brix percentages in neonatal Arabian foals from birth up to 21 days of age

The aim of this study was to evaluate changes in the serum immunoglobulin G (IgG) and serum total protein (STP) concentrations and serum Brix percentages of neonatal Arabian foals during first 3 weeks of life. Blood samples were collected from 12 apparently healthy foals by jugular venipuncture at birth and at 12-hours, 24-hours, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15 and 21 days of age. Serum IgG and STP concentrations and Brix percentages were measured by the radial immunodiffusion assay, and digital STP and Brix refractometers, respectively. Based on the serum IgG concentrations measured at 24 h, two foals were diagnosed with failure of transfer of passive immunity (FTPI). While IgG concentrations were determined using the data of foals with adequate transfer of passive immunity, other calculations were made using the data of all foals. The mean IgG concentration of the foals increased from birth (<200 mg/dl) to 12 (2068.5 mg/dl) and 24 h (2184.7 mg/dl), and progressively decreased up to 21 days of age (1318.5 mg/dl). The serum IgG concentrations at 12 h were highly correlated with each of the IgG concentrations measured over the 21-day period. The serum IgG and STP concentrations and Brix percentages of the foals diagnosed with FTPI at 12 h did not reach the adequate strata over time. These results suggest that foals can be reliably tested for passive immunity status at 12 h after birth.

Evaluation of refractometry methods for estimating passive immunity status in neonatal foals

The objective of this cross-sectional study was to determine the accuracy of the digital Brix and serum total protein (TP) refractometers for estimating different passive immunity status in neonatal foals. In total, 18- to 40-h old purebred Arabian foals (n = 185) were used. Serum TP concentrations, total solid percentages and IgG concentrations were measured with a digital serum TP refractometer, digital Brix refractometer and the gold standard radial immunodiffusion (RID) assay, respectively. Correlation coefficients were calculated between the refractometer and RID assay results. A receiver operating characteristic analysis was used to select the optimal cut-offs for both refractometers. Test performance and agreement were evaluated using diagnostic test characteristics at optimal thresholds and areas under the ROC curve, and by calculating Cohen's kappa coefficient. The sensitivity and specificity of the digital Brix refractometer at optimal cut-offs (≤7.8%, ≤7.9%, ≤8.2%, ≤8.3%, ≤9.0%) were 100 and 69.3%; 100% and 68.5%; 70.5% and 71.0%; 88.3% and 85.5%; 88.1% and 76% to estimate RID-IgG of <400 mg/dL, <800 mg/dL, <1500 mg/dL, <2500 mg/dL and < 3000 mg/dL, respectively. The sensitivity and specificity of the digital serum TP refractometer at optimal cut-off (≤4.6 g/dL, ≤4.6 g/dL, ≤4.8 g/dL, ≤5.0 g/dL, ≤5.4 g/dL) were 100 and 69.3%; 100% and 72.8%; 90% and 72.8%; 72.9% and 83.9%; 84.4% and 88% to estimate RID-IgG of <400 mg/dL, <800 mg/dL, <1500 mg/dL, <2500 mg/dL and < 3000 mg/dL, respectively. In conclusion, the refractometers showed a good potential as screening tools for the estimation of different IgG concentrations in neonatal foals.