Maternal Recognition of Pregnancy - Anatomy & Physiology

Overview

Species	Cow	Ewe	Sow	Mare	Queen	Bitch
Preganacy Recognition Factor	Bovine Interferon tau	Ovine Interferon tau	Oestrogen and Pituitary Prolactin	Unidentified	Pituitary Prolactin	None Required

The free-floating blastocyst produces specific proteins that signal to prevent luteolysis.
Sheep blastocysts produce ovine interferon tau (OIFN-τ)
Cattle blastocysts produce bovine interferon tau (BIFN-τ)
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.

The ruminant conceptus undergoes rapid elongation between day 14 and 16.
During this period, IFN-τ is secreted at high levels before decreaseing.
Small embryos produce much less IFN-τ than larger embryos.
There is a hige proportion of embryo loss in the first 3 weeks of gestation, as small embryos fail to secrete enough IFN-τ in this critical period. Thus they do not block luteolysis.
- This may be related to poor nutritional status of the mother.