Injections of Oxytocin in the Early Postpartum Period Affect the Status of Mammary Tight Junctions in Swine

The goal of this project was to determine if injections of oxytocin in the early postpartum period affect the quality of mammary tight junctions, milk composition and immune status of sows and piglets. Post-parturient sows received im injections of either saline (CTL, n = 10) or 75 IU of oxytocin (OXY, n = 10). A total of 4 injections were given, the first 12 h after the end of farrowing, then twice per day (08:00 and 16:30). Milk samples were obtained following an iv injection of 20 IU of oxytocin before the first treatment injection, before the second injection, and 24 and 48 h after the last injection. Standard milk composition was measured as well as the Na/K ratio, and IGF-1, IgG and IgA concentrations. Blood samples were obtained from sows prior to the first, second and last milkings to measure prolactin, IGF-1, lactose, IgG and IgA concentrations. On d 5 of lactation, a blood sample was obtained from 3 piglets per litter to measure immunocrit and concentrations of IGF-1, IgG, IgA, and interleukin-2 (IL-2). The MIXED procedure of SAS was used for statistical analyses and means were compared using the Tukey’s test. Circulating concentrations of prolactin, IGF-1, lactose and IgA in sows did not differ between treatments at any time (P > 0.10) but OXY sows had less IgG than CTL sows (P < 0.01) before the second oxytocin injection. There were also differences in milk composition before the second injection, with OXY sows having more IGF-1 (P < 0.01), DM (P < 0.05), protein (P < 0.001), energy (P < 0.05), and IgA (P < 0.01) and a greater Na/K ratio (P < 0.001) than CTL sows. These differences were not seen in the next 2 milk samples, except for protein and IgA that still tended (P < 0.10) to be greater in OXY vs CTL sows 24 h (for protein) and 48 h (for IgA) after the last injection. Values for immunocrit, IGF-1, IgG and IgA in piglet blood did not differ between treatments (P > 0.10), whereas concentrations of IL-2 tended to be greater (P< 0.10) in OXY compared with CTL piglets. Data demonstrate that injecting oxytocin in the early postpartum period increases leakiness of the mammary tight junctions, improves composition of early milk, and potentially affects immune status in neonatal piglets.