Artificial Long Estrus Protocols Administered Prior to Progesterone Increase Endometrial Uterocalin Expression in Anestrous Mares.
Authors: Silva Elisa S M, Vaz Isabela S, Rodrigues Tamiris S, Brandão Felipe Z, Oquendo Pedro S, Oquendo Fabiana M G, Beletti Marcelo E, Cuervo-Arango Juan
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Uterocalin (P19), a uterine lipid-binding protein essential for early embryonic survival, is expressed at higher levels in the endometrium of acyclic mares when they undergo artificially-induced prolonged estrus before progesterone treatment, yet the optimal oestrogen dosing regimen has remained unclear. This 2021 study investigated whether a simplified two-dose oestradiol benzoate protocol could match the uterocalin-stimulating effects of the traditional five-dose approach in 15 anestrous mares, with all animals subsequently receiving long-acting progesterone. Both extended-estrus protocols (whether using two or five oestradiol administrations) significantly elevated endometrial P19 expression compared to a single-dose control, producing comparable uterine oedema scores and plasma hormone profiles despite their different dosing schedules. The practical implication for practitioners preparing recipient mares in field conditions is substantial: the two-dose long-estrus protocol achieves equivalent endometrial priming with fewer injections and simplified handling, though confirmation through subsequent embryo transfer success rates would strengthen the evidence base for this more economical approach. Whilst these findings suggest that the reduced protocol offers genuine utility for stud farms and breeding operations, clinicians should recognise that enhanced uterocalin expression alone does not guarantee improved pregnancy outcomes, and further research tracking actual embryo viability and implantation rates remains necessary to validate this simplified preparation method.
Read the full abstract on PubMed
Practical Takeaways
- •For preparing anestrous recipient mares, the simplified 2-injection estradiol benzoate protocol (3 mg and 5 mg on Days -7 and -4) is as effective as the traditional 5-injection protocol for promoting uterocalin expression, making it more convenient for farm management
- •Long estrus protocols consistently outperform single-dose estrogen treatments for improving endometrial receptivity markers in acyclic mares, supporting their use in recipient mare preparation
- •While these protocols improve uterocalin expression (a marker of embryo support), field practitioners should await further research confirming improved embryo survival and pregnancy rates before changing current practice protocols
Key Findings
- •Both long estrus protocols (LE2 and LE5) significantly increased endometrial uterocalin (P19) expression compared to short estrus protocol (P < 0.05)
- •The simplified 2-administration long estrus protocol (LE2) produced equivalent P19 expression to the 5-administration protocol (LE5), with no statistical difference between them
- •Both long estrus protocols maintained high uterine edema (score 2-3) for at least 6 days, indicating sustained estrogenic stimulation
- •The LE2 protocol is more practical for field conditions while maintaining the reproductive benefits of longer estrogen exposure in acyclic mares