Prolactin levels and duration of postpartum anoestrus in lactating ewes

Abstract

THE length of the postpartum anoestrous period in sheep is related to the degree of mammary stimulation. If the ewe is milked by hand twice a day or ‘dried off’ immediately after parturition, the first oestrus occurs 30–40 d postpartum in the ‘Préalpes du Sud’ breed; if the ewe is nursing her lamb(s)—suckling 10–12 times per day—postpartum anoestrus lasts for 60–80 d (ref. 1). A similar phenomenon has been described in women; menses reappear within 10 weeks postpartum in 80% of women who are not breast feeding, but in only 10% of those who are². In both species suckling is accompanied by large discharges of oxytocin and prolactin; this reflex secretion of prolactin decreases as lactation progresses, and is almost nonexistent by the time of return of cyclical ovarian activity.