Mid-infrared spectroscopy for a rapid assessment of immunoglobulins G level in bovine colostrum

The concentration of immunoglobulins G (IgG, g/l) defines colostrum quality in cattle. By convention, colostrum with IgG<50 g/l is not recommended for calves feeding in the first h of life due to insufficient antibodies level. On average, 15% of cows produce colostrum of unacceptable quality in dairy farms, exposing the calf to greater risk of mortality and morbidity and impairing the future heifer’s performance. In this study, first colostrum samples (521 Holstein cows) were collected between 2019 and 2020 in 9 farms within 6 h from calving. Each sample was aliquoted for IgG and protein content determination via gold standard, i.e. radial immunodiffusion and Kjeldahl, respectively, and for prediction of total protein content via mid-infrared spectroscopy (MIR) using the prediction model developed for mature milk. Before MIR analysis, colostrum samples were diluted in pure water (1:1) to reduce matrix density and avoid clogging issues. We demonstrated that MIR-predicted protein content was significantly correlated with both IgG (r=0.87) and protein content (r=0.97) measured with gold standard. Moreover, receiving operating characteristic analysis (ROC) showed that MIR-predicted protein content was able to accurately identify low- from high-quality colostrum samples regardless of the IgG threshold considered (50, 70, or 90 g/l). In parallel, we evaluated the discriminant ability of colostral refractive index (BRIX), whose performance were similar to those of MIR-predicted protein content. The area under the ROC curve was excellent, being 0.85 for MIR-predicted protein content and 0.83 for BRIX when IgG threshold was set at 50 g/l. The cut-off identified for MIR-predicted protein content was 13.08, 13.28, and 14.64% for IgG threshold at 50, 70, and 90 g/l, respectively. Findings do suggest that milk labs equipped with MIR devices may offer an indirect quality evaluation of bovine colostrum for screening purposes and to support farmers’ decision making. Finally, our results are of interest for industries that use bovine colostrum as an ingredient.