Endometrial Histomorphometry of Anestrous Mares Under the Influence of Different Embryo Transfer Hormonal Protocols.
Authors: Silva Elisa S M, Leite Raíssa O, Maciel Luciana F S, Francia Camila C D A, Padovani Carlos R, Oliveira-Filho José P, Meira Cezinande
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Reproductive specialists managing embryo transfer programmes in anestrous mares must balance the need for endometrial preparation against the risk of hormonal over-stimulation, making this histomorphometric study particularly relevant to clinical practice. Twenty-six anestrous mares received one of four protocols: escalating doses of estradiol benzoate (EB) alone—2.5 mg, 5 mg, or 10 mg across consecutive days—each followed by 1,500 mg of long-acting progesterone (LAP4), or LAP4 monotherapy; endometrial biopsies were analysed for luminal and glandular epithelial height, endometrial thickness, and glandular density before treatment and five days post-progesterone, with cyclic mares sampled during oestrus and day 5 post-ovulation serving as controls. By day 5, the three EB-primed groups (EB2.5LAP4, EB5LAP4, EB10LAP4) demonstrated comparable endometrial morphometry to naturally cycling control mares across all measured parameters, whilst the LAP4-only group showed similar luminal epithelium height and endometrial thickness but significantly reduced glandular density and glandular epithelium height compared with controls. These findings demonstrate that oestradiol priming substantially enhances glandular development and secretory capacity in the anestrous endometrium, suggesting that even minimal EB dosing (2.5 mg) may suffice for adequate endometrial conditioning whilst minimising hormone exposure—a practical consideration for practitioners balancing efficacy with cost and physiological safety in embryo transfer recipients.
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Practical Takeaways
- •Estradiol priming before progesterone is essential for optimal endometrial development in anestrous mares undergoing embryo transfer; progesterone alone is insufficient
- •Lower estradiol doses (2.5–5 mg) appear as effective as higher doses (10 mg) when combined with long-acting progesterone, potentially reducing drug costs and handling stress
- •By day 5 post-treatment, EB-primed mares achieve endometrial characteristics comparable to naturally cycling mares, suggesting this is an appropriate window for embryo transfer procedures
Key Findings
- •EB5LAP4 and EB10LAP4 protocols produced similar endometrial morphometric changes with no dose-response relationship observed
- •All EB-treated groups achieved endometrial morphometry similar to cyclic control mares by day 5 post-treatment
- •LAP4 alone produced reduced glandular density (GD) and glandular epithelium height (GEH) compared to control group, indicating estradiol priming is important for glandular activity
- •Luminal epithelium height, glandular epithelium height, endometrial thickness, and glandular density were the key morphometric parameters affected by hormonal protocols