The objective of this study was to determine whether lactation function could be reinitiated after a period of extended milk stasis. Involution was induced by milk stasis in lactating Holstein cows for a period of 11 d. On d 11, one side of the mammary gland was milked twice daily for 3 d. The contralateral side remained unmilked for the 14-d experimental period. Cows were slaughtered, and mammary tissue was collected from both udder halves for further analysis. Mammary secretion volume was partially restored in the milked udder half, but reestabished milk yields were variable among cows. A partial recovery of lactation function was further indicated by elevated levels of lactose and protein profiles resembling milk in mammary secretions from the milked glands. Lactose and protein profiles from the unmilked glands were similar to those of glands undergoing involution. Lactoferrin levels were elevated in secretions from the milked and unmilked udder halves. Casein and lactoferrin synthesis by mammary explants and β-casein and lactoferrin mRNA abundance in mammary tissues corresponded to protein profiles from milked and unmilked mammary secretions. α-Lactalbumin mRNA was variable but was more abundant in the milked glands compared with the unmilked glands. Lectin fluorescence microscopy for soybean agglutinin preferentially stained the apical surface of the mammary epithelial cells from the milked glands. Staining was absent in the unmilked glands and suggested resumption of lactation function in all such milked glands. These results suggest that mammary involution can be partially reversible after 11 d of milk stasis.
Key words
mammary gland
involution
milk proteins
Abbreviation key
Lf
lactoferrin
REM
remilked
SBA-FITC
soybean agglutinin conjugated with fluorescein isothiocyanate
Supported by the Illinois Agricultural Experiment Station as part of Hatch Project 35-0315 and by the Cooperative State Research, Education and Extension Service, USDA under projects AG 94-37024-0849 and AG 97-35206-5098.