Cellular studies of mammary tissue from cows hormonally induced into lactation: lactose and fatty acid synthesis.

Temporal changes in ability of mammary gland to synthesize lactose and fatty acids were identified during the treatment of cows hormonally induced to lactate, and animal differences were compared to subsequent milk production. Hormonal treatment involved 17 beta-estradiol + progesterone on days 1 to 7 and dexamethasone on days 17 to 19. Mammary tissue obtained by biopsy on days 0, 8, 16, and 26 of treatment was examined for biosynthetic capacity by tissue slice incubations. In terms of peak daily milk yield, one cow was very successful (greater than 30 kg), two were intermediate (9 to 10 kg), and one cow was unsuccessful (less than 3 kg). Differences between cows in the capability to synthesize lactose and fatty acids were evident as early as day 8 and were further magnified by day 16. In particular, the tissue from the successful cow was undergoing lactogenesis by day 8 while this was not evident until the day 16 biopsy sample in the less successful cows. In contrast to the other cows, tissues from the unsuccessful animal regressed in its ability to synthesize lactose and fatty acids between day 16 and 26. Relative differences between animals in measurements of metabolic capacity were consistent with subsequent milk production.