Postponing first colostrum collection: impact on immunoglobulin G in goat colostrum

This experiment was motivated by the need to understand the impacts of delaying the first colostrum collection on immunoglobulin G (IgG) concentrations in goat colostrum, addressing a gap in caprine-specific research, despite its significance in dairy farming. Concurrently, we examined the relationship between colostral IgG, total protein (TP) and Brix values. Two colostrum samples were collected from 56 Saanen goats, one from each udder half. The first sample was collected from the right teat immediately postbirth, and the second sample was collected from the left teat at one of the predetermined postpartum intervals: 0, 4-6, 8-10, or 12-14 h postpartum, each time interval comprising 14 goats. Colostral IgG was determined by ELISA, Brix was determined by digital refractometry, and TP was determined by the Bradford protein method. Sperman's correlations and Lin's concordance correlation coefficient were used to determine the direction and strength of the association and to assess agreement (prediction accuracy) between methods, respectively. Receiver operator characteristic analysis was used to determine Brix and TP thresholds for predicting good-quality colostrum using several cut-offs (20, 30, 40, and 50 g/L IgG). Mean (± SD) for colostral IgG, Brix, and TP were 54 ± 22.6 g/L, 22 ± 5.0%, and 12 ± 2.8 g/dL, respectively. The statistical analysis did not provide evidence of a significant impact of time of first collection (up to 14 h postpartum), on IgG, Brix, and TP. Brix and IgG values exhibited both a high degree of correlation (r = 0.89-90) and concordance (ρ_c = 0.89-90), indicating a strong and reliable relationship between the two measurements. The prevalence of samples ≥ 20, 30, 40, and 50 g of IgG/L were 96, 88, 71, and 54%, respectively. Optimal Brix and TP thresholds predicting IgG ≥ 20, 30, 40, and 50 g/L IgG were 13.8, 17.5, 20.1, and 22.5%, and 6.8, 9.3, 10.8, and 11.1 g/dL, respectively. Increasing the IgG threshold resulted in lower sensitivity but higher specificity for estimating colostral IgG using Brix or TP values. The present findings indicate that delaying the first colostrum collection up to 14 h postpartum did not result in conclusive changes in colostral IgG concentration, Brix values, or total protein levels. Our results also confirm the reliability of Brix refractometry as an on-farm tool for estimating IgG concentrations in goat colostrum. These results are particularly relevant to intensive dairy systems, offering insights to enhance colostrum management and task prioritisation, especially during the bustling kidding periods.