Resumption of ovarian activity in post-partum ewes: Role of the uterus

Abstract

The effect of the involuting uterus on luteal life span and pattern of secretion of progesterone was studied in suckled ewes and in ewes with lambs removed on Day 1 after an autumn lambing (breeding season). Total hysterectomy, performed the day of parturition or the day after, resulted in all cases within two weeks in the formation and development of persistent (more than 65 days) and actively progesterone-secreting corpora lutea immediately after the first post-partum LH surge. However, during the early post-partum period, progesterone secretion increased at a slower rate than later at the time of resumption of cyclic ovarian activity in control ewes. It may be inferred from these results that frequent short duration of first post-partum ovarian cycles results from: (1) the luteolytic influence of the involuting uterus due to an increased and prolonged release of prostaglandin F 2α as found by other workers; (2) an incompleted restoration of LH release leading to insufficient follicular growth and maturation.