Shamay, A., Agricultural Research Organization (ARO), Volcani Center, Institute of Animal Science, PO Box 6, Bet Dagan, 50250, Israel
Shapiro, F., Agricultural Research Organization (ARO), Volcani Center, Institute of Animal Science, PO Box 6, Bet Dagan, 50250, Israel
Mabjeesh, S.J., Hebrew University of Jerusalem, Faculty of Agricultural, Department of Animal Science, PO Box 12, Rehovot 76100, Israel
Silanikove, N., Agricultural Research Organization (ARO), Volcani Center, Institute of Animal Science, PO Box 6, Bet Dagan, 50250, Israel

Mammary involution is triggered by local stimuli, but the precise mechanism has not been defined. Milk stasis accumulate local signals, which makes the tight junctions (TJ) leaky. The aim of the study was to check the hypothesis that casein hydrolyzates (CNH) compromise TJ integrity and dry up milk secretion. A single dose of CNH transiently (12 to 24 h) compromised TJ integrity in the treated udder. This was associated by a transient (12 to 96 h) decline in milk secretion. No such changes were recorded in the contralateral gland that served as a control. Four repeated doses of CNH after each milking caused drastic changes in mammary secretion and composition, which were associated with irreversible cessation of milk secretion within 96 h. No such changes were recorded in goats treated with de-phosphorylated casein (control). We conclude that CNH are the milk-borne factors that cause the disruption of TJ integrity and induction of involution, and that the serine-Ps in the CNHs are essential for the excretion of biological activity. © 2002 Elsevier Science Inc. All rights reserved.