Shamay, A., Institute of Animal Science, Volcani Center, P.O. Box 6, Bet Dagan, 50250, Israel
Shinder, D.A., Institute of Animal Science, Volcani Center, P.O. Box 6, Bet Dagan, 50250, Israel
Bruckental, I., Institute of Animal Science, Volcani Center, P.O. Box 6, Bet Dagan, 50250, Israel
Silanikove, N., Institute of Animal Science, Volcani Center, P.O. Box 6, Bet Dagan, 50250, Israel

The regulation of milk constituents, synthesis and secretion in tissue cultures of the bovine mammary gland was altered by a whey fraction of bovine milk. α-Casein gene expression, casein secretion and fatty acid synthesis were inhibited by the whey fraction in a dose-dependent manner. The whey fraction inhibited the enhancement activity of prolactin on α-casein gene expression and fatty acid synthesis, and also inhibited casein secretion to the medium, in explants cultured in a medium with or without prolactin. No effect on the expression of the β-lactoglobulin gene was found.