Histology of induced bovine lactogenesis

Nine cycling nonlactating dairy cows were treated hormonally to induce lactation with progesterone, estradiol-17beta, and dexamethasone. Mammary tissue biopsies were taken on days 18, 21, and 23 after initiation of treatment (different three cows for each period). First milking was initiated on day 21 in the latter two groups. Mean differences in tissue development (percent area) between day 18 and 23 were, epithelium + 11.1%, stroma -25.9%, alveolar lumen + 13.9%, adipose + 1.58%, duct - 974%, and + 15 nuclei/alveolar section. On day 18 epithelia containing small lipid droplets predominated but were replaced with mixed lipid droplets by day 23. Epithelia day 18 had elongated dark staining nuclei. Epithelia on day 23 had spherically shaped nuclei often containing several nucleoli and an increased cytoplasmic/nuclear ratio. Marked histological development occurred from 18 to 23 days after initiation of treatment. Mammary tissue development in nongravid hormonally treated animals was equal to or greater than 2-wk-prepartum tissue but less than 2-day-prepartum tissue for natural lactations.