Effects of secretion removal on bovine mammary gland function following anextended milk stasis

The objective of this study was to determine whether lactation function cou ld be reinitiated after a period of extended milk stasis. Involution was in duced 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 contr alateral side remained unmilked for the 14-d experimental period. Cows were slaughtered, and mammary tissue was collected from both udder halves for f urther analysis. Mammary secretion volume was partially restored in the mil ked udder half, but reestabished milk yields were variable among cows. A pa rtial recovery of lactation function was further indicated by elevated leve ls of lactose and protein profiles resembling milk in mammary secretions fr om the milked glands. Lactose and protein profiles fi om the unmilked gland s were similar to those of glands undergoing involution. Lactoferrin levels were elevated in secretions from the milked and unmilked udder halves. Cas ein and lactoferrin synthesis by mammary explants and beta-casein and lacto ferrin mRNA abundance in mammary tissues corresponded to protein profiles f rom milked and unmilked mammary secretions. alpha-lactalbumin mRNA was vari able but was more abundant in the milked glands compared with the unmilked glands. Lectin fluorescence microscopy for soybean agglutinin preferentiall y stained the apical surface of the mammary epithelial cells from the milke d glands. Staining was absent in the unmilked glands and suggested resumpti on of lactation function in all such milked glands. These results suggest t hat mammary involution can be partially reversible after 11 d of milk stasi s.