WAP-Brk mammary glands exhibit delayed post-lactational involution. A, Carmine alum staining of inguinal mammary gland whole mounts, INV D6. B, H&E staining of inguinal mammary glands from INV D1-INV D6. 200 × magnification. C, Quantification of mammary epithelium from H&E sections, INV D1-D14. Inset, epithelial content quantified by area on Day 6. Asterisks signify statistically significant differences between groups (P < 0.05).