We investigated the components of mammary gland secretions in dairy cattle after drying off, and found marked changes. In mammary gland secretion protein, the concentration of lactoferrin (Lf) reached maximum level at 7 days after drying off, and somatic cell counts (SCC) showed over 400* 10 sup (4) cells/ml at 15 days after drying off, mainly CD11 b sup (+) cells. These findings indicated that Lf induced apoptosis of mammary gland (MG) epithelial cells and phagocytosis by increased leukocytes. On the other hand, CD4 sup (+)/CD8 sup (+) ratio was increased just after drying off, and the peak of both CD4 sup (+)/CD sup (8)+ ratio and B-B sup (2+) lymphocyte counts occurred at 20 days before parturition. The principal lg of colostrum for neonatal immunity is lgG1 , which reached at maximum concentration just before parturition. Moreover, high CD4 sup (+)/CD8 sup (+) cell ratio of bovine peripheral blood mononuclear cells were induced in vitro by coculture of Lf. Therefore, Lf may induced the CD4 sup (+) T lymphocyte infiltration into the MG in non-lactating period. Our findings suggested that MG maternal antibody synthesis in the non-lactating period changed dramatically due to the physiological effects of Lf and known hormonal effects. Nihon Chikusan gakkaiho, 75 (2) : 205-212. 2004