295 Effects of a Supraphysiological Oxytocin Injection After Parturition on Blood-Milk-Barrier Closure and Igg Transfer into Milk in Dairy Cows

Abstract

Abstract Oxytocin (OT) can affect the blood-milk-barrier integrity by modulating the closure of tight junctions. Earlier research demonstrated a transfer of circulating immunoglobulins (Ig) into milk upon OT application during an LPS-induced mastitis. The role of OT in colostrogenesis, i.e., IgG transfer into colostrum, is not fully understood. Our study aimed at retarding the postpartum closure of the blood-milk-barrier and concomitantly prolonging the transfer of IgG into colostrum of dairy cows by a supraphysiological OT injection. Multiparous Holstein cows (n = 28) were enrolled. Blood and milk samples were collected at the first 2 milkings after parturition and milk yields were recorded. Ten cows received 50 IU OT i.v. at 30 min after the first milking (OT+30), 9 cows were injected 50 IU OT i.v. at 120 min before the second milking (OT-120), and 9 cows remained untreated (CTRL). Cows were milked at 6.7 ± 0.7 h after parturition (first milking) and 11.5 ± 0.3 h later (second milking). Milk was analyzed for fat, protein, lactose and IgG, serum albumin (SA), and electrolytes (Na, K, Cl) concentrations and for lactate dehydrogenase (LDH) activity. Concentration of α-lactalbumin (α-LA) was measured in blood plasma. Data were evaluated using a mixed model (SAS) with group, milking number, and group x milking number as fixed effects, and cow as random subject. In all groups, concentrations of protein, IgG, SA, LDH in milk decreased from first to second milking, while lactose content in milk increased (P < 0.05). Milk yield and milk fat content did not differ between first and second milking (P > 0.05). Concentration of α-LA in plasma tended to decrease from first to second milking. Treatments did not affect changes in blood and milk from first to second milking. In conclusion, a single injection of supraphysiological OT either at 30 min after the first milking postpartum or 2 h before the second milking postpartum did not retard the closure of the blood-milk-barrier in dairy cows. Furthermore, OT application did not prolong the active transport of IgG into milk after the first milking.