Oxytocin release and milk ejection parameters during milking of dairy ewes in and out of natural season of lactation

Two groups of 40 milking Lacaune ewes were monitored during their natural (spring) and off-season (autumn) lactation. Serial samples collected before, during and after milkings were used to study oxytocin release in relation to milk flow patterns recorded during milking. Overall, oxytocin release was significant in 92.5% of the ewes but only 56% of them exhibited clear alveolar milk ejection. Oxytocin is essential for milk ejection but no correlation between oxytocin ejection and milk fraction volumes of milking was detected. Baseline oxytocin and progesterone concentrations and the proportion of cisternal milk were significantly higher in autumn than in spring. It was concluded that clear alveolar emission of milk during milk flow recordings are not reliable indicators of milk ejection efficiency in high producing animals with large cisternal volumes. Likewise, the amount of oxytocin released during milking cannot be used to select the animals best adapted to machine milking or the best producers. Nevertheless, this study suggests that luteal oxytocin has a major role in milk transfer between milkings.