Oestrogen production by the preimplantation donkey conceptus compared with that of the horse and the effect of between-species embryo transfer.

The research investigates and compares the oestrogen production in preimplantation conceptuses of horses and donkeys and explores the effects of transferring embryos between the two species. Main findings reveal differences in aromatase activity and distribution in the examined tissues and show that the maternal environment does not significantly affect aromatase distribution.

Research Overview

• The research studies the aromatase activity and distribution in the yolk sac, chorionic girdle, and allantochorion of preimplantation conceptuses of both horses and donkeys.
• The approach for measuring aromatase distribution was the incorporation of a labelled precursor, [3H]androstenedione, into oestrone and oestradiol-17 beta.
• The researchers further controlled the experiment’s environment by performing between-species embryo transfers and observing the effects on aromatase distribution.

Key Findings

• Aromatase activity in a donkey conceptus was found to be similar across all tissues examined.
• In the horse conceptus, however, the activity was generally lower and displayed a specific relationship where the chorionic girdle showed more activity than the yolk sac, which, in turn, had more activity than the allantochorion.
• More labelled precursor was incorporated into oestradiol-17 beta by the donkey’s extra-embryonic tissues as compared to those of the horse.
• Aromatase activity in the chorionic girdle did not exhibit a progressive decline before migration into the endometrium on Day 36 to form the endometrial cups, contrary to previous findings.

Effects of Between-Species Embryo Transfer

• In the case of a donkey conceptus that was transferred and carried in a mare’s uterus, the chorionic girdle failed to invade the surrogate horse endometrium. However, the aromatase activity remained high in the tissue at Day 42.
• When observing transferred donkey-in-horse conceptuses, the distribution of aromatase aligned with the fetal (donkey) genotype, rather than the maternal (horse) genotype, Thus, indicating the maternal environment does not have a significant impact on the distribution of aromatase.