Maternal stress during gestation might be one of the causes of decreased piglet survival, and the impairment of the transfer of maternai immunity to the neonate might be involved. The present study involved sows raised during gestation in a group housing system on slat (SL, n=18) or in an enriched group housing system (on straw with larger pens, E, n=19), where rates of piglet pre-weaning mortality were steadily different (E: 8% vs. SL: 15%). Sows were blood sampled on the day of gestation (DG) 105 and one day after farrowing (L 1) for blood ce li numeration and haptoglobin level measurement. Mammary secretions were collected at farrowing (LO, 1-2 h after the birth of the first piglet) and 4 days later (L4, milk collection after 1 ml oxytocin administration), and cells were phenotyped by flow cytometry. At DG105, E sows had lower haematocrit (P(It]0.05) and granulocyte counts (P[It]0.05) but comparable haptoglobin levels than SL sows. Haptoglobin levels increased from DG1 05 to L 1 in both groups (P[It]0.001 ). The absolute numbers per ml of mammary secretion of CD172+ cells in the gate of polynuclear cells (neutrophils) and of CD172+ (monocytes), CD2+CD8+high (cytotoxic T cells), CD2+CD8+1ow (memory T cells) and CD2+CD8- cells in the gate of mononuclear cells increased between LO and L4 (P [lt] 0.001 ), and were greater in E than SL sows at L4 (tendancy at P [lt] 0.1 for CD172+ cells and P [lt] 0.05 for others). Thus, sow's immune activation around farrowing was different in the two systems and associated with consequences on the numbers of immune cells transmitted by the mother to the young in milk but not colostrum.