The use of laparoscopic intrauterine insemination to deposit semen directly into the tip of the uterine horn thus bypassing the involuting uterus ensures fertilization in ewes induced to ovulate at 3 to 5 weeks post-partum. Acceptable pregnancy rates are achieved if embryos from post-partum donors are transferred to a normal uterine environment (60%; Wallace, Robinson & Aitken, 1989a) but embryos rarely survive when transferred or returned to a post-partum uterus (0-25%; Wallace, Robinson & Aitken, 1989b; McKelvey, Wallace, Robinson & Aitken, 1989). Furthermore, when conceptus development was assessed at Day 16 after insemination only a small sub-set of post-partum ewes remained pregnant, suggesting that any defect in the maternal/embryonic dialogue which may inhibit the re-establishment of pregnancy in post-partum ewes occurs prior to this stage (Wallace, Ashworth, Aitken & Cheyne, 1991).

In the current study a novel blastocyst transfer procedure was developed to test whether the post-partum uterus can support conceptus development during the period of rapid growth coincident with the maternal recognition of pregnancy.