Figure 4.

Time course of IgG secretion by the mammary gland reveals substantially greater amounts secreted in transition milk. (A) Representative Western blot showing colostrum (COL) and transition milk IgG levels in periodic postpartum milking (1, 4, 16, 28, 40, and 52 hr). (B) Graph showing changes to IgG concentration and colostrum/transition milk volume during the periodic post-partum milking (n = 9). The threshold line (at 50 g/L) indicates minimum concentration recommended for feeding by industry standards. Data show that colostrum/milk IgG secretion in the mammary gland continues beyond the first milking (colostrum), with a gradual decline over the sampling period in transition milk. IgG concentrations were not significantly different (ns) between <1-, 4-, and 16-hr milking. Increases to volume was not significantly different between <1-, 4-, and 16-hr milking, but progressively increased at the 28-, 40-, and 52-hr milkings. (C) Graph showing total postpartum mammary IgG secretion (cumulative values) across the different timepoints indicating the overall mammary output over time. Notable are the increased combined IgG output over 4- and 16-hr milking that are timepoints without significant changes to volume. Overall, there remains a linear increase in total mammary IgG released over time (R² = 0.7076; P = 0.0004). Of the total mammary IgG released, 25% is contained in colostrum and 32.3% is contained in the 4- and 16-hr transition milk. (D) Comparing total IgG produced in the first milking compared with transition milk combined (4 to 52 hr) indicated that an ~3-fold significantly higher levels of total IgG is secreted as part of transition milk (****P < 0.00001).