Hormonal and immunological changes in blood and mammary secretion in the sow at parturition.

The purpose of the present study was to record possible variations of estradiol-17 beta (E2) and cortisol concentrations, and parameters related to granulocyte phagocytosis in mammary secretions from healthy sows at parturition. The study was comprised 8 primiparous sows (Landrace x Yorkshire). Blood and mammary secretion samples were collected twice daily from 3 d before (only blood) until 3 d after farrowing. Estradiol-17 beta and cortisol concentrations were determined in plasma and in cell-depleted skimmed mammary secretions. Phagocytic capacity of polymorphonuclear cells (PMN) was assessed in whole blood and in cell suspensions derived from mammary secretions. Opsonic activity was assessed in serum and in cell-depleted skimmed mammary secretions. The 2 assays were based on chemiluminescence. Estradiol-17 beta concentration in plasma decreased (P < 0.001) directly after parturition. In skimmed secretions, the highest E2 concentration was recorded in the first sample after parturition and decreased (P < 0.01) thereafter. The highest cortisol concentration in plasma was recorded in the evening before parturition (P < 0.01). In skimmed secretions, there was no significant variation in cortisol concentration. The concentrations of both steroid hormones were lower in mammary secretions than in plasma. The phagocytic capacity of PMN in blood and mammary secretion, expressed as peak chemiluminescence per PMN, showed no significant change. This was also true for the opsonic activity in serum. In skimmed secretions the opsonic activity increased (P < 0.01) after parturition. These data emphasize the differences between plasma and mammary secretion concentrations of steroid hormones as well as between systemic and mammary gland immune competence. Regarding the phagocytosis process in mammary secretions, the part directly related to the PMN function seemed not to be altered at parturition compared with later on in lactation, whereas the part related to opsonic activity seemed to be impaired at parturition. The latter may play a role in the development of coliform mastitis at this time.