Novel Aspects of the Physiology of Pregnancy in Domestic Ruminants.

Mammals exhibit unique and highly variable mechanisms for the establishment and maintenance of pregnancy. Ruminants (e.g., sheep, cows, and goats) have novel mechanisms whereby the conceptus (embryo and its extra-embryonic membranes) signals for the establishment of pregnancy and exhibits unique metabolic pathways favoring conceptus development. Embryos of ruminants reach the spherical blastocyst stage at 5 to 10 mm in diameter and then elongate rapidly to elongated filamentous conceptuses of greater than 250 mm as they make contact with the uterine luminal epithelium (LE) for implantation. During conceptus elongation the trophectoderm cells secrete interferon tau (IFNT), a novel pregnancy recognition signal for ruminants to ensure maintenance of a functional corpus luteum (CL) to secrete progesterone (P4) required for pregnancy. P4 induces uterine epithelia cells to express the endogenous Jaagsiekte Retrovirus (enJSRV) that may transactivate toll-like receptors 7 and 8 in the conceptus trophectoderm to induce secretion of IFNT, a classical viral-antiviral mechanism. IFNT silences expression of receptors for estradiol (E2) and oxytocin (OXTR), which abrogates the mechanism whereby oxytocin from CL and posterior pituitary would otherwise induce large pulses of prostaglandin F