Validating a refractometer to evaluate Immunoglobulin G concentration in Jersey colostrum and the impact of multiple freeze-thaw cycles on evaluating colostrum quality
The objectives were: 1) validate an on farm method utilizing refractometry to rapidly and accurately determine immunoglobulin (IgG) concentration in Jersey colostrum and 2) evaluate the impact of freeze thaw (FT) cycles on radial immunodiffusion (RID) and refractometry to determine IgG concentration in bovine colostrum. Samples (n=58; 3 L) of first-milking colostrum were collected from a single dairy in northwestern Iowa. Samples were analyzed within 2 h of collection for IgG concentration by RID, %Brix and refractive index (nD) by refractometer and an estimate of IgG concentration by colostrometer. Samples were then frozen, placed on dry ice and transported to the laboratory at Iowa State University (Ames, IA). All samples arrived frozen and were placed in a -200C manual defrost freezer until further analysis. On day 7 (1FT), 14 (2FT) and 1 year (3FT) all samples were thawed, re-analyzed by RID, %Brix, nD and colostrometer and re-frozen. Fresh colostrum, had a mean IgG concentration, as determined by RID, of 72.91 mg/mL (SD = 3.30), mean %Brix of 21.21 (SD = 0.34) and mean nD of 1.3669 (SD = 0.0074). Immunoglobulin G concentration as determined by RID and IgG as estimated by colostrometer were impacted by the number of FT cycles. The estimates for IgG concentration by RID were greater in fresh and 1FT samples as compared to 2FT and 3FT samples (72.91, 75.38, 67.20 and 67.31 mg IgG/mL, respectively). The colostrometer reading was lower in 1FT samples compared to fresh and 2FT samples. There was no impact of multiple FT cycles on nD, or %Brix reading. In fresh samples, IgG concentration was moderately correlated with nD (r=0.79), %Brix (r = 0.79) and colostrometer reading (r = 0.79). Diagnostic test characteristics utilizing the recommended cut-point of 1.34966 nD resulted in similar sensitivities for 1FT and 2FT samples (94.87 and 94.74%, respectively). Cut-points of 18, 19, 20 and 21 %Brix were evaluated on Fresh samples. 18 and 19 %Brix cut-points resulted in the greatest sensitivities (92.31 and 84.62%) and specificity (94.74 and 94.74%, respectively). Using the 18% cut-point resulted in 94.83% of the samples being correctly classified. This data supports the use of refractometry (nD and %Brix) to accurately and rapidly determine IgG concentration in fresh Jersey colostrum. Additionally the data suggests that IgG concentration as determined by RID is impacted by multiple FT cycles, whereas estimates obtained via refractometry are not impacted by multiple FT cycles.
Keywords: Colostrum Jersey Refractometer