Maternal Recognition of Pregnancy - Anatomy & Physiology

Ruminants

The free-floating blastocyst produces specific proteins that signal to prevent luteolysis.
Sheep blastocysts produce ovine interferon tau (OIFN-tau)
Cattle blastocysts produce bovine interferon tau (BIFN-tau)
Interferon tau is a small protein produced by trophoblastic cells of the blastocyst.
It is present in the uterus at day 13-21 after ovulation.
It is not luteotrophic, so does not enhance progesterone production by the corpus luteum.
Instead, it binds to the uterine endometrium and inhibits the synthesis of oxytocin receptors.
In addition to preventing the upregulation of oxytocin receptors, interferon tau binds to the apical portion of uterine glands to promote synthesis of proteins that are critical for embryonic survival pre-implantation.
As a result, there is no production of the luteolytic factor PGF2α and the corpus luteum is maintained.
The corpus luteum then produces progesterone to maintain the pregnancy.