In the bovine species, 25%-40% of all embryos are lost during the first month of pregnancy. During this period, dramatic cellular transformations in both the maternal epithelium and the conceptus are accompanied by the transient expression at the materno-fetal interface of potent molecules ensuring the survival, accommodation, and growth of the conceptus.
The most important of these molecules in ruminant species is probably interferon-tau (IFN-т), the pregnancy recognition signal, produced by the bovine conceptus between Days (d) 12-28 of pregnancy (P), peaking at d15P-d19P. Indeed, IFN-т inhibits the expression of estrogen receptors in the ovine uterine epithelium, preventing up-regulation of the oxytocin receptor (OTR) by estradiol and subsequent generation of luteo-lytic pulses of prostaglandin (PG) F2a by oxytocin (OT). In cattle, the relationship between IFN-т, estrogen receptor, and OTR is not clear, and IFN-т may directly inhibit the expression of OTRs.
Pregnancy or intrauterine treatment with IFN-т also induces the expression of several proteins that can be classified as chemokines, antiviral proteins, cytokines, cell surface markers, signal transducers, and transcription factors.