A, mean daily milk yield of left (L) and right (R) glands before and after unilateral cessation of twice-daily milking for 1, 2 or 3 weeks. Values are means ±s.e.m. when n≥ 2 (values of n are given inthe text). B-F, morphology of mammary tissue from glands milked twice daily (B) or unmilked for 3 days (C), 1 week (D), 2 weeks (E) or 3 weeks (F). B, arrow, large secretory alveolus; s, alveolar secretion. C, arrow, columnar alveolar cell; n, polymorphic neutrophil. D, large arrow, alveolar cells; arrow, alveoli; small arrow, apoptotic bodies. E, arrow, alveolar cell with pycnotic nucleus and indistinct cell membrane; a, alveolar lumen containing flocculent material; m, myoepithelial cell; n, neutrophil. F, large arrows, lobules of ductules; e cuboidal epithelial cell; f, fibrocollagenous stroma; small arrows, body defence cells; arrowhead, apoptotic bodies. Scale bar, 50 μm; applies to all panels.