Hormonal changes during parturition in heifers and goats are related to the phases and severity of labour

Parturition is a natural event that involves stress and pain for the mother . We thus hypothesized that levels of stress hormones measured during partu rition could reflect levels reached in response to severe discomfort and pa in of other kinds as well. The aim of this study was therefore to determine whether plasma concentrations of cortisol, adrenaline, noradrenaline, beta -endorphin, met-enkephalin, vasopressin and oxytocin vary depending on the phase and severity of labour in dairy heifers (ten) and dairy goats (six), and how these hormones interact with each other. Blood samples were taken o nce a day for 3 days before labour and for 3 days afterwards and at predete rmined phases during labour. All heifers delivered one calf and five of the m needed obstetrical assistance. Two of the goats delivered one kid, and fo ur had mins; all kidded without help. The cortisol concentration peaked whe n the calf and the first kid were born. In the heifers, plasma adrenaline i ncreased after delivery, while the noradrenaline concentration did not chan ge significantly in heifers that needed assistance, but increased during ex pulsion in heifers calving without help. In the goats, adrenaline and norad renaline concentrations increased in association with expulsion of the firs t kid. The P-endorphin concentration increased during labour in goats. In h eifers that needed assistance, beta-endorphin concentration increased 1 h a fter labour but there was no change in heifers that did not need assistance . The mel-enkephalin concentration was elevated during expulsion in heifers and fluctuated in the goats. Both oxytocin and vasopressin increased durin g expulsion in both groups of heifers, but vasopressin increased four times more in heifers needing assistance. In the goats, oxytocin reached its hig hest levels just as the feet of the first kid became visible, and vasopress in peaked as the head emerged. Parturition look longer in heifers that need ed assistance than in those that did not. II is concluded that, even though the pattern of change differed between hormones during labour, the changes were related to the phases of labour. A longer labour therefore meant that the hormone concentrations stayed elevated for longer. Vasopressin reached high levels in goats and was the only hormone for which plasma concentrati ons were higher in heifers that needed assistance than in those that did no t, indicating that this hormone is released in order to deal with the pain- related stress associated with labour.