Cortisol, adrenalin, noradrenalin and oxytocin release and milk yield during first milkings in primiparous ewes

Abstract

The experiment was conducted to verify whether the first machine milkings post-partum cause stress in primiparous ewes, and to study the profile of cortisol (CORT), adrenalin (AD), noradrenalin (NOR), oxytocin (OT) and milk parameters during the first milkings. Twelve Lacaune ewes milked twice daily were used in this experiment. Milk yield and milk composition were determined during the first 15 days of lactation. Blood samples were taken before, during and after the morning milking on days 1, 4, 7 and 15. Baseline levels of AD, NOR and OT did not change significantly during the successive milkings. However, basal levels of CORT varied between days and the highest level was observed before the first machine milking. From days 1 to 4, there was no significant release of OT, however on days 7 and 15, the onset of milking induced a significant and abrupt increase in OT levels. In contrast, AD and NOR measured on day 1 were higher than on day 15. On days 1 and 7, CORT release was greater than on day 4, but CORT release observed on days 1 and 7 did not differ from that on day 15. OT released during machine milking was significantly associated with milk yield, milk fat and milk protein, however total CORT release was negatively associated with milk yield. At the same time, three ewes never released OT during milkings. These ewes produced significantly less milk (660±140 ml/day) than other ewes (1386±115 ml/day), and two of these three ewes presented high AD and NOR levels. In the present research, milk yield, OT, AD and NOR levels suggest that the first milkings are important stressors, however the majority of the ewes had adapted to machine milking by day 15.