Main content area

Technical note: Evaluation of digital refractometers to estimate serum immunoglobulin G concentration and passive transfer in Jersey calves

McCracken, M.M., Morrill, K.M., Fordyce, A.L., Tyler, H.D.
Journal of dairy science 2017 v.100 no.10 pp. 8438-8442
Holstein, Jersey, blood sampling, blood serum, brix, calves, immunoglobulin G, models, protein content, rapid methods, refractive index, Arizona
Previous data have demonstrated that refractometers can be used to estimate serum IgG, and that a cut-point of 7.8% Brix should be used to identify failure of passive transfer (FPT) in 1-d-old Holstein calves. The objective of the present study was to validate the use of refractometry to estimate serum IgG concentrations and evaluate FPT in Jersey calves. Blood samples (n = 97) were obtained from 1- to 3-d-old Jersey calves and centrifuged at 3,300 × g for 20 min at 25°C. Serum was analyzed for % Brix, total protein (TP), and refractive index (nD) using a Sper Scientific Digital Refractometer (model #300036, Sper Scientific, Scottsdale, AZ) within 12 h of sampling. Samples were then frozen and later analyzed in the laboratory for IgG by radial immunodiffusion. The mean serum IgG concentration for all calves was 23.7 mg/mL (SD = 12.5), with a range of 2.3 to 65.5 mg/mL. Mean serum % Brix was 8.9 (SD = 1.1; range 6.5 to 12.0). Serum % Brix was moderately correlated with IgG concentration (r = 0.77). Total protein and IgG were moderately correlated (r = 0.790). Regression was used to determine cut-points for approximately 10, 12, and 14 mg of IgG/mL and to determine the sensitivity and specificity of refractometry to identify FPT (serum IgG <10 mg/mL at 24 h of life). Brix cut-points analyzed were 7.1, 7.3, and 7.6%; TP cut-points were 4.6, 5.0, and 5.5 g/dL; and nD cut-points were 1.34332, 1.34271, and 1.3448, respectively, for 10, 12, and 14 mg of IgG/mL. The 7.3% Brix and 4.6 g/dL TP cut-points resulted in the greatest percentage of samples being correctly classified. These data suggest that digital refractometry is an acceptable and rapid method to estimate immunoglobulin G in Jersey calf serum.