The influence of fetal genotype upon endometrial cup development and PMSG and progestagen production in equids.

The influence of fetal genotype upon gonadotrophin (PMSG) and progestagen production in mares and donkeys during the first half of pregnancy was examined. The production of PMSG was greatly reduced in mares carrying mule conceptuses and greatly increased in donkeys carrying hinny conceptuses. Fetal genotype had no obvious influence upon progestagen production in mares, but donkeys carrying hinny conceptuses showed extremely high peripheral plasma progestagen concentrations when serum PMSG levels were elevated. Fetal genotype profoundly influences the intensity and rate of success of the maternal leucocyte response directed against the endometrial cups. The suggestion is advanced that PMSG may constitute an immuno-protective barrier around endometrial cup cells which partly protects the cells from attack by sensitized maternal lymphocytes.