Origin of PMSG/eCG Hormone

PMSG (or Equine Chorionic Gonadotropin/eCG) is secreted by the endometrial cups of the equine placenta and is a hormone of which origin?

Correct Answer: Foetal origin

PMSG (eCG) is secreted by the endometrial cups of the equine placenta. Although the endometrial cups are located in the maternal uterine tissue, they are formed from foetal trophoblast cells that invade the endometrium around day 36–38 of pregnancy. Therefore, PMSG is considered a hormone of foetal origin.

Timeline of PMSG in Mares

• Chorionic girdle forms at ~day 25 of pregnancy
• Trophoblast cells invade the endometrium at ~day 36–38 forming endometrial cups
• PMSG secretion begins from day 40, peaks at days 60–70, then declines
• Detectable until day 120–150 of pregnancy

Detection Tests for PMSG

• Aschheim-Zondek (A-Z) test: Detects PMSG in serum of pregnant mare
• Cuboni test: Detects estrogen in urine of pregnant mare