Plasma prolactin in the sow with emphasis on variation in resumption of ovarian activity after weaning.

Plasma prolactin in the sow was studied during pregnancy, lactation and during the post weaning period. The ovarian activity was monitored hy progesterone determinations. In the pregnant sows (2 sows) there was a distinct increase in prolactin values ahout a week before parturition, amounting to maximum levels around parturition. A moderate decrease in prolactin values during the lactation period (3 sows) was observed. After weaning the prolactin values dropped immediately to basal levels. Of the 91 sows studied in the post weaning period 72 sows resumed cyclic ovarian function within normal time (10 days) after weaning while 19 sows had delayed resumption of ovarian activity. The prolactin patterns in sows with prolonged periods of ovarian inactivity were similar to those seen in normal sows. None of our results indicate that post weaning anoestrus is caused by prolonged hyperprolactinaemia after weaning.