Selected Metabolites Found in Equine Oviductal Fluid do not Modify the Parameters Associated to Capacitation of the Frozen-thawed Equine Spermatozoa In Vitro.
Authors: Fernández-Hernández Pablo, García-Marín Luis Jesús, Bragado María Julia, Domingo Andrés, González-Fernández Lauro, Macías-García Beatriz
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Achieving reliable in vitro fertilisation in horses remains elusive, with incomplete sperm capacitation suspected as a significant barrier to protocol development. Researchers investigated whether five metabolites naturally present in equine oviductal fluid—myoinositol, lactate, glycine, β-alanine and histamine—could enhance capacitation markers in frozen-thawed stallion spermatozoa when added to culture medium over a 2-hour incubation period. Using flow cytometry and computer-assisted sperm analysis across multiple functional endpoints (motility, viability, mitochondrial membrane potential, acrosome reaction, reactive oxygen species production and protein tyrosine phosphorylation), the team found no significant improvements in any measured parameter, regardless of metabolite concentration tested. Whilst this null result may seem disappointing, it meaningfully narrows the focus for future investigations and suggests that either higher physiological concentrations of these metabolites, different combinations, or additional signalling molecules present in oviductal fluid warrant exploration. For practitioners involved in equine breeding programmes, particularly those utilising cryopreserved semen, these findings underscore that simple metabolite supplementation alone is unlikely to be the missing piece in optimising in vitro fertilisation protocols.
Read the full abstract on PubMed
Practical Takeaways
- •Current knowledge of individual metabolites in mare reproductive tract fluid has limited application to improving in vitro equine sperm handling—further research on metabolite combinations or concentrations is needed
- •Practitioners using frozen-thawed equine semen for breeding should not expect simple metabolite supplementation to improve in vitro fertilization outcomes based on this evidence
- •The incomplete success of equine IVF protocols appears related to factors beyond the metabolites tested; alternative approaches to achieving sperm capacitation should be investigated
Key Findings
- •Five metabolites found in equine oviductal fluid (myoinositol, lactate, glycine, β-alanine, histamine) at tested concentrations produced no significant effects on frozen-thawed sperm motility, viability, or acrosome reaction
- •Mitochondrial membrane potential, reactive oxygen species production, and protein tyrosine phosphorylation were not modified by metabolite addition
- •The tested dosages of individual metabolites did not enhance sperm capacitation parameters in modified Whitten's medium
- •Study demonstrates that metabolite concentration matching equine oviductal fluid levels may require optimization beyond the ranges tested