Dynamics of mammary secretory cells in lactating dairy ewes

This study investigated the morphometrical changes in mammary glands of 25 Sarda dairy ewes (5 per period) at 10 days before parturition (LateP); 30, 60, 150 days in milking (30, 60 and 150DIM) and 8 days after the dry off (8IN). Total number of alveoli and mammary epithelial cells (MEC) decreased during lactation, being the highest in LateP (2.54×106 and 60.6×106, respectively), intermediate at 30DIM (1.36×106 and 27.7×106, respectively) and the lowest afterwards (0.56×106 and 12.3×106, respectively, at 8IN). Number of MEC per alveolus (20.8±1.58, mean±SE) and estimated milk yield per MEC (3.8×10-5±6.21×10-6) did not differ between periods. Mammary gland volume and internal morphology (number of MEC per alveolus, number of alveoli per udder half and volume of the alveolar lumen) explained, respectively, 62 and 47% of the variability of daily milk yield. The volume or weight of the mammary gland, which represent the black box in deterministic models, was more efficient in forecasting milk yield than the internal morphology of the udder, normally used in biomechanistic models.