Estimate of serum immunoglobulin G concentration in Jersey calves using refractometry
Previous data from our lab demonstrated that refractometry could be used to estimate serum IgG in Holstein calves; data suggested that a %Brix cut-point of 7.8 should be used to identify failure of passive transfer in 1 day old Holstein calves. The objective of the present study was to validate the use of refractometry to determine serum IgG concentrations and evaluate failure of passive transfer in Jersey calves. Blood samples (n=108) were obtained from 1-3 day old Jersey calves and centrifuged at 3,300 x g for 20 minutes at 25 0 C. The serum was analyzed for %Brix and refractive index (nD) using a digital refractometer and IgG concentration was determined by radial immunodiffusion. The mean serum IgG concentration for all calves was 23.7 mg/ml (SD = 12.2), with a range of 2.2 to 65.0 mg/ml. Mean serum %Brix for all calves was 8.8 (SD = 1.1), with a range of 6.5 to 12.0. Mean serum nD for all calves was 1.34596 (SD = 0.00173), with a range of 1.34280 to 1.35110. Serum %Brix and nD were positively correlated with IgG concentration (r = 0.74 and 0.73 respectively; n=107). Regression analysis was used to determine cut points for 10, 12, and 14 mg IgG/mL and diagnostic characteristic test characteristics were calculated to determine the sensitivity and specificity of refractometry to identify failure of passive transfer (serum IgG < 10mg/mL at 24 h old). The %Brix were 7.1, 7.3, and 7.6 and the nD cut-points were 1.24332, 1.34271 and 1.3448, respectively. The 7.3% Brix and 1.34271 nD cut-point resulted in the greatest percentage of samples being correctly classified (92.59 and 93.52%, respectively) and the best combination of diagnostic test characteristics. Our data suggest that a digital refractometer is an acceptable, rapid and low cost method to estimate immunoglobulin G in Jersey calf serum but that breed-specific cut points may need to be utilized.
Keywords: Passive transfer, Refractometer, Jersey, Validate