Evolution of oxytocin, prolactin and cortisol release during the first milkings of primiparous ewes

摘要

This experiment was conducted to verify whether the first post-partum milking induces oxytocin (OT), prolaclin (PRL) and cortisol (CORT) release and lo study the evolutionary profile of these hormones during the first milkings, in eight primiparousewes. Blood samples were taken and milk yield and milk composition recorded on days 1, 4, 7, and 15 after parturition. From day 1 to 4, there was no significant increase in OT release. However, on day 7, the maximum OT concentration was observed at 0.5min. after the onset of milking and OT levels decreased after the end of the milking. The highest OT release was measured on day 15. During the milking. PRL release increased slowly; the maximum level was observed at 0.5min. after the onset of the milkingand plateaued afterwards. During this study, PRL release induced by milking was shown to increase. The highest PRL release was measured on day 15. The CORT levels increased significantly 6mn after the start of milking, and the naximum CORT level was recorded at lOmin. The CORT release increased significantly hroughout lactation with the highest release of CORT being measured on day 1 and the lowest on day 4 post-partum. The present experiment supports the hypothesis that OT, PRL and CORT released duringmilking machine was influenced by the day of lactation. However, OT, PRL and CORT release decreased or increased at different levels during the lactation days studied. These variations suggest that neither the udder sensitivity nor the activation of theascending nervous pathways is involved in this mechanism of regulation. The results confirmed also that in early lactation, many ewes did not adapt to the milking machine. These ewes not adapted to milking machine never released OT during the experimental milkings, had minimal PRL release and produced significantly less milk (660.00 +/- 140ml) than the other ewes (1279.00 +/- 160.00ml).