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Evaluation of a Brix Refractometer to Estimate Serum Immunoglobulin G Concentration in Neonatal Dairy Calves
The objective of this study was to evaluate the utility of a digital Brix refractometer for the assessment of success of passive transfer of maternal immunoglobulin, as compared to the measurement of serum total protein (STP) by refractometry. Blood samples (n = 400) were collected from calves 3 to 6 days of age. Serum IgG concentration was determined by radial immune-diffusion (RID), and STP and percent Brix (%Brix) using a digital refractometer. The mean [± standard deviation (SD)] IgG concentration was 24.1 ± 10.0 g/L with a range from 2.1 to 59.1 g/L. The mean STP concentration was 6.0 ± 0.8 g/dL with a range from 4.4 to 8.8 g/dL. The mean %Brix concentration was 9.2 ± 0.9% with a range of 7.3 to 12.4%. Brix percentage was highly correlated with IgG [correlation coefficient (r) = 0.93]. Test characteristics were calculated for the assessment of failure of passive transfer (FPT; serum IgG < 10 g/L). The sensitivity and specificity of STP at 5.5 g/dL were 76.3% and 94.4%, respectively. However, it is noteworthy that relatively few samples had IgG levels < 10 g/L. As such, further evaluations of different populations are warranted. A receiver operating characteristic curve was created to plot the true positive rate against the false positive rate for consecutive %Brix values. The optimal combination of sensitivity (88.9%) and specificity (88.9%) was at 8.4% Brix. Serum total protein was also positively correlated with %Brix (r = 1.00) and IgG (r = 0.93). The results of the current project suggest that dairy producers can successfully monitor their colostrum management and the overall success of passive transfer using a digital Brix refractometer to estimate IgG concentration of colostrum and calf serum.
Keywords: passive transfer, refractometer, calf