Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: January 5, 2004
Publication Date: June 20, 2004
Citation: Annen, E.L., Capuco, A.V., Gentry, P.C., Baumgard, L.H., Collier, R.J. 2003. Late gestation and advanced lactation at cessation of milking do not delay mammary epithelial apoptosis in dairy cattle. Journal of Dairy Science [abstract]. 86(Suppl 1):117
Advanced pregnancy and concurrent lactation at cessation of milking are two factors thought to slow mammary involution in dairy animals. Our objective was to characterize the temporal pattern of apoptosis in the bovine mammary gland following milk stasis. Serial mammary biopsies were performed on 11 Holstein cows during late lactation and the dry period. Cows were dried-off 60d before expected calving. Mammary biopsies were taken at -5, 0, 1, 2, 3, 4, 5, 6, 7, 8, 10, 14, and 21d relative to cessation of milking. Tissues were fixed in neutral buffered formalin, and paraffin sections were subjected to TUNEL assay for immunohistochemical detection of apoptotic cells. The incidence of mammary epithelial cells undergoing apoptosis was lowest in lactating tissue, peaked (P< 0.0001) 2d following cessation of milking and then declined through d8. At d2, the incidence of apoptosis was 4 to 8-fold greater than that in lactating tissue. By d8, the number of apoptotic mammary epithelial cells did not differ (P > 0.05) from pre-stasis values. Rodents and ewes typically initiate apoptosis by 2d post-stasis and reach peak apoptosis at approximately 4d. Because these species are not typically in advanced gestation and lactation when milk removal ceases, we hypothesized that onset of apoptosis would be slower and incidence of apoptosis reduced in cows as compared to sheep and rodents. Our data indicate that onset of epithelial apoptosis in cows is rapid but transient and alveolar integrity is maintained throughout the 21d post dry-off. Further, a second wave of apoptosis involving intralobular stromal elements appears to initiate at d4 and peak at d5 (P<0.05). The balance between apoptosis and cell proliferation during this time frame is currently under investigation. Data are consistent with rapid initiation of tissue remodeling of both epithelium and stroma during the dry period of dairy cows.