Maternal Recognition of Pregnancy Following Blastocyst Transfer to Ewes Induced to Ovulate at 28 Days Post-Partum

Abstract

In ewes that have recently lambed, the use of exogenous hormones to induce ovulation followed by laparoscopic intrauterine insemination to ensure fertilization, results in the production of viable oviductal-stage embryos. These embryos develop to term if transferred to a normal uterine environment on Day 3 of the cycle (Wallace et al., 1989a) but rarely survive beyond the duration of a normal oestrous cycle if returned to a post-partum uterus (Wallace et al., 1989b). In the ewe, the maternal recognition of pregnancy depends on adequate secretion of the conceptus interferon, ovine trophoblast protein 1 (oTP-1) into the uterine lumen. This protein interacts with its receptor on the maternal endometrium to locally suppress expression of the uterine oxytocin receptor. This in turn prevents establishment of a positive feedback loop between episodic ovarian oxytocin secretion and uterine prostaglandin F2α (PGF2α) release which would normally induce luteal regression at the end of the oestrous cycle. The present study examined the nature of these phenomena in the early post-partum ewe.