Administration of 2.5 mg of estradiol followed by 1,500 mg of progesterone to anovulatory mares promote similar uterine morphology, hormone concentrations and molecular dynamics to those observed in cyclic mares.

The study hypothesizes and provides evidence that administering 2.5 mg of estradiol followed by 1,500 mg of a long-acting progesterone induces similar morphological and molecular changes in the uterine tracts of anovulatory mares as observed in cyclic mares.

Research Methodology

• To test their hypothesis, the researchers examined the changes in estrogen and progesterone receptors in various reproductive states of mares (anestrous, transitional and cyclic) using RT-qPCR and immunohistochemistry.
• The team also evaluated other physiological aspects such as uterine edema, tonus (muscle tone) and the plasma profiles of estrogens and progesterone.
• They conducted endometrial biopsies on anestrous and transitional mares at three separate intervals – right before the injection of estradiol, 48 hours after its administration and five days after the administration of the long-acting progesterone. In cyclic mares, biopsies were taken during estrus and five days post ovulation.

Findings

• The study found similarities in estrogen peaks between treated and cyclic groups following the injection of a single dose of estradiol. It also reported maximum uterine edema in both groups.
• Uterine tone in the treated mares was shown to increase to diestrus levels after the administration of 1,500 mg of long-acting progesterone.
• The study also reported comparable changes in relative abundance of progesterone receptor, estrogen receptor α and estrogen receptor β when a progesterone stimulated endometrium was compared with its estrogen-stimulated counterpart. This was observed in both cyclic and non-cyclic treated mares.
• In non-cyclic mares however, a noticeable decrease in progesterone receptors in the endometrial glandular epithelium was not observed five days after the administration of long-acting progesterone – a phenomenon usually observed five days post ovulation in cyclic mares.

Conclusion

• The research concluded that the administration of 2.5 mg of estradiol benzoate followed by 1,500 mg of long-acting progesterone can induce changes in uterine morphology, hormone concentrations and molecular dynamics that mirror those observed in cyclic mares. These changes include similar endometrial edema, uterine tonus and changes in relative abundance of PR, ERα and ERβ transcripts, as well as comparable estradiol and estrogen conjugate plasma concentrations.