Comparison of creamatocrit and protein concentration in each mammary lobe of the same breast: does the milk composition of each mammary lobe differ in the same breast?

Objective: We sought to determine if different mammary lobes produce milk of varying composition.

Study Design: Seventeen mothers were enrolled in this study. Foremilk was obtained from three nipple openings on each breast. After the breastfeeding session, hindmilk was sampled in the same manner. We measured creamatocrit (CrCt) and analyzed the protein concentration. Data were analyzed with the paired t test and Wilcoxon signed-rank sum test where appropriate. Coefficient of variance (COV) was calculated to identify the variation of protein content among different mammary lobes.

Results: The fat and protein contents of the foremilk and hindmilk from each milk duct differed despite being expressed from the same breast. When we compared the CrCt values and protein content obtained from three ducts, a greater than 5% difference between the maximum and minimum value was observed in 64 out of 68 breasts (94%) for CrCt and in 61 out of 68 breasts (91%) for protein content. The mean COV of protein content in each breast was 13.2 +/- 8.0 (range, 1.2-45.3).

Conclusions: These study results demonstrate that milk synthesis differs in each mammary lobe, even in the same breast. The degree of fullness in each mammary lobe seems to play the most important role in the fat content. The protein content in the milk from each mammary lobe is determined by other factors, presumably by the feedback inhibitor of lactation, accumulated in the corresponding mammary lobe.