Effects of Preimplantation Bovine and Porcine Conceptuses on Blood Flow and Steroid Content of the Uterus

The embryonic signal that initiates luteal maintenance occurs by about Day 12 in the sow (Dhindsa and Dzuik, 1968), Day 13 in the ewe (Moor and Rowson, 1966), and Day 16 in the cow (Betteridge et al., 1978). The mechanism responsible for maintenance of a corpus luteum (CL) during early pregnancy, and in particular the way in which the embryo influences this process, is not clearly understood but may involve a local affect of the conceptus on utero-ovarian blood flow. Data presented by Ford et al. (1976) demonstrated a preferential effect of the ovine and bovine conceptus for reducing in vitro constriction of the uterine artery supplying the gravid horn on Day 15 and Day 17 postcoitus, respectively. Transient increases in blood flow to gravid uterine horns of ewes have been observed on Days 13 to 15 of pregnancy (Greiss and Anderson, 1970).