Effects of lactation, suckling and oxytocin on post-partum ovulation and oestrus in ewes.

The first ovulation and first oestrus after parturition were recorded in four groups of Merino ewes which: (a) reared their lambs normally, (b) were allowed to suckle their lambs only during three 1-hr periods each day, (c) had their lambs removed on the day after birth, or (d) had their lambs removed on the day after birth and were injected intramuscularly with 5 i.u. oxytocin ten times each day for the first 17 days after parturition. Ewes with restricted suckling activity or with lambs removed on the day after birth showed their first post-partumovulation and oestrus at about the same times as ewes which reared their lambs normally. Ewes injected with oxytocin showed their first post-partum ovulation and oestrus significantly earlier than ewes in the other three groups.