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.