Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: March 12, 2008
Publication Date: July 1, 2008
Citation: Soberon, F., Lukas, J.L., Van Amburgh, M.E., Capuco, A.V., Overton, T.R. 2008. The effects of increased milking frequency during early lactation on metabolism and mammary cell proliferation in Holstein cows. [abstract].Journal of Dairy Science.
Primiparous (n=30) and multiparous (n=30) cows were assigned randomly at calving to one of 2 treatments to evaluate metabolic and mammary cell responses to increased milking frequency (IMF). Controls were milked twice daily (2X) for 119 d and the IMF group was milked four times daily (4X) from d 2 until d 21 postpartum and 2X from d 22 until d 119. Early lactation IMF did not affect overall milk yield (42.0 vs. 40.6 kg/d; P > 0.10). An interaction of treatment by week (P < 0.01) indicated that IMF cows yielded 4.8 kg/d more milk than control cows during wk 2 and 3 but comparable amounts of milk thereafter. Although there was no interaction of treatment and parity (P = 0.31), a trend (P = 0.08) for an interaction of treatment by parity and week suggested that overall responses were more pronounced in primiparous cows. When cows subjected to mammary biopsies were excluded, an overall interaction of treatment by parity existed (P < 0.01) such that milk yield was increased throughout the study period by IMF (40.1 vs. 34.2 kg/d) in primiparous but not multiparous cows (47.1 vs. 50.1 kg/d). Plasma nonesterified fatty acids were elevated in multiparous cows subjected to IMF (679 vs. 468 µEq/L) but not in primiparous cows (583 vs. 562 µEq/L; treatment by parity, P < 0.05). Plasma ß-hydroxybutyrate was not affected by IMF. Mammary tissue was biopsied from a subset of cows (n=8 per lactation group and treatment) at calving, 21 d postpartum, and 75 d postpartum and used for immunohistochemical localization of Ki-67. A treatment by day interaction (P = 0.03) indicated that IMF cows had fewer labeled epithelial cells than controls at d 21 (0.31 vs. 0.82%) but more labeled epithelial cells at d 75 (1.37 vs. 0.65%). Overall, results suggest that metabolic health may influence the milk yield response of cows to early lactation IMF. Further analysis of mammary cellular dynamics is needed to determine specific mechanisms for milk yield responses to early lactation IMF.