Post weaning plasma progesterone, prolactin and environmental influence in the resumption of ovarian activity in sows

Plasma progesterone levels were determined three days after weaning in 151 sows Landrace x Large White. Furthermore, the influence of bromocriptine (Parlodel, Sandoz) was studied on the resumption of ovarian activity in 19 sows during the hot season. An increased progesterone base-line level was shown during the June-July-August period as compared with May and September-October. No correlation was found between progesterone levels and the percentage of sows which returned to estrus 10 days after weaning except when progesterone levels reached and exceeded 0.9 ng/ml; in this case, no sow resumed ovarian activity in normal time. Bromocriptine treatment had no influence on the resumption of ovarian activity, suggesting that prolactin is not involved in the lack of estrus after weaning. An influence of environmental factors is also suggested.