Relationships between antral follicle count and reproductive characteristics of embryo-recipient mares.
Authors: Delchiaro Sofia Botsaris, Oliveira Pedro Victor de Luna Freire, Júnior Rubens José Paulossi, Gonçalves Gabrieli Dutra, Morotti Fábio, Seneda Marcelo Marcondes
Journal: Journal of equine veterinary science
Summary
# Editorial Summary: Antral Follicle Count and Embryo Recipient Success Antral follicle count (AFC) has emerged as a potential marker of ovarian reserve in mares, yet its relevance to embryo-recipient suitability remained unclear. Botsaris and colleagues examined 77 mares (43 with low AFC ≤11 follicles; 34 with high AFC >11 follicles) undergoing embryo transfer, with acyclic recipients receiving synchronisation protocols combining oestradiol benzoate and progesterone to mimic cyclicity, whilst measuring conception rates alongside uterine and endocrine parameters at transfer. Counterintuitively, conception rates favoured low-AFC recipients overall (79.1% versus 61.8%), with the most striking difference appearing in the high-AFC anoestrous group, which achieved only 37.5% pregnancy compared to 80–83.3% in other combinations. Cyclic mares consistently outperformed anoestrous recipients (81.4% versus 58.8%), and uterine oedema was significantly greater in anoestrous animals regardless of AFC status. These findings suggest that whilst reproductive seasonality is the dominant factor influencing recipient success, AFC may serve as an additional screening tool—particularly cautioning against selecting high-AFC anoestrous mares—and highlight the importance of careful endocrine synchronisation in seasonal breeders seeking to expand the recipient pool beyond naturally cycling candidates.
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Practical Takeaways
- •When selecting embryo-recipient mares, prioritize cyclic mares over anestrous mares—reproductive status is more predictive of success than AFC alone, with cyclic recipients showing 23% higher conception rates
- •Mares with lower antral follicle counts may actually be more suitable recipients despite conventional thinking; consider AFC ≤11 as potentially advantageous, particularly if the mare is cycling
- •In anestrous mares used as recipients, expect reduced conception rates (especially with high AFC) and implement supplemental progesterone protocols; reproductive seasonality significantly impacts uterine receptivity independent of other factors
Key Findings
- •Embryo-recipient mares with low AFC (≤11 follicles) had significantly higher conception rates (79.07%) compared to high AFC (>11 follicles: 61.76%)
- •Cyclic mares achieved conception rates of 81.40% versus anestrus mares at 58.82%, with the poorest outcome in high-AFC anestrus recipients (37.50%)
- •Reproductive seasonality influenced uterine edema, with anestrus mares showing higher degree of edema than cyclic mares, affecting pregnancy establishment
- •Optimal conception rate of 83.33% was achieved in cyclic recipients with high AFC, while low-AFC cyclic recipients achieved 80% conception rate