Embryo transfer into anestrous recipient mares prepared using clomiphene citrate and short-acting progesterone.
Authors: Derbala M K, Mosallam T E, Sindi R A
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Embryo transfer remains a cornerstone of equine breeding programmes, yet preparing recipient mares—particularly those in seasonal or prolonged anoestrus—remains a practical challenge in the field. Researchers in this 2024 study investigated whether a simplified oral protocol combining clomiphene citrate (250 mg for 4 days) and short-acting progesterone (Altrenogest for 6 days) could reliably condition acyclic mares with small or absent follicular structures, comparing outcomes in 60 treated anoestrous mares against 12 naturally cycling controls. The protocol proved remarkably successful, achieving an 83.3% pregnancy rate in the anoestrous group versus 66.6% in cycling controls, with treated mares developing significantly elevated serum progesterone concentrations (P < 0.001) that matched or exceeded natural cycling levels, whilst maintaining appropriate oestradiol responses. For practitioners managing breeding programmes, particularly in regions with pronounced seasonal breeding restrictions, this approach offers a practical means of extending the breeding season and utilising recipient mares year-round without reliance on injectable hormones or complex synchronisation protocols. The oral administration route and short treatment window suggest potential advantages in compliance, cost-effectiveness and mare welfare compared to traditional recipient preparation methods.
Read the full abstract on PubMed
Practical Takeaways
- •This oral protocol offers a practical alternative to traditional hormone treatments for preparing out-of-season mares as embryo recipients, potentially improving convenience and cost-effectiveness
- •The 83.3% pregnancy rate in acyclic mares treated with this protocol exceeds the control cycling group, suggesting the induced uterine environment may be favorable for embryo implantation
- •Practitioners can use this approach to extend breeding season or utilize non-cyclic mares for embryo transfer programs, expanding genetic improvement opportunities year-round
Key Findings
- •Clomiphene citrate (250 mg for 4 days) followed by Altrenogest (6 days) successfully induced cyclicity in 60 non-cyclic mares with follicles ≤15 mm
- •Pregnancy rate in treated acyclic mares (G1) was 83.3% compared to 66.6% in naturally cycling control mares (G2)
- •Serum progesterone concentrations were significantly higher in treated acyclic mares than cycling controls (P<0.001)
- •No significant difference in estradiol concentrations between groups during diestrus phase (P>0.05)