Diagnostic accuracy of a Brix refractometer to estimate porcine colostrum quality

Background: The objective of this study was to investigate the validity of the Brix refractometer to accurately estimate immunoglobulin G (IgG) concentrations in porcine colostrum, using radial immunodiffusion (RID) as a reference standard. Methods: Eighty-seven composite colostrum samples were collected from sows on a single pig farm between September 2022 and September 2024. Brix measurements were compared with IgG RID test results for each colostrum sample. Results: Brix measurements ranged from 10.80% to 28.05% (mean = 20.13; standard deviation = 3.78). Samples from 40 of the 87 sows (45.98%) were below the colostrum quality threshold of 50 g/L IgG. Pearson's correlation coefficient revealed a strong correlation of 0.81 (p < 0.001) between Brix (%) and RID IgG concentration. Receiver operating characteristic (ROC) curves were constructed to determine the optimal threshold to accurately determine poor colostrum quality (<50 g/L IgG) using the Brix refractometer. At an RID IgG concentration threshold of less than 50 g/L, ROC analysis (Youden index) defined an optimal Brix threshold of 20.05% (sensitivity = 0.75, specificity = 0.75 and area under the curve = 0.76). Limitations: The retrospective design of this study led to some inherent limitations with the quality and quantity of the data collected. Conclusions: The results of this study indicate that the Brix refractometer can be used as an accurate pen-side tool for estimating IgG concentrations in porcine colostrum.