Plasma relaxin, estrogens and progestogens concentration in coldblooded and hot-blood mares in the second half of gestation.
Authors: Kędzierski Witold, Kowalik Sylwester, Maśko Małgorzata, Janczarek Iwona, Bełkot Zbigniew
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Breed-related variation in reproductive hormone profiles during equine pregnancy has received limited investigation, particularly in coldblooded mares, despite known differences affecting clinical interpretation of results. Witold Kędzierski and colleagues analysed blood samples from 94 healthy mares in late gestation (36 coldblooded and 58 hotblood animals) to establish comparative reference ranges for relaxin, estrone sulphate, estradiol-17β and progestogens using species-specific immunoenzymatic assays. Coldblooded mares demonstrated substantially lower hormone concentrations across all measured parameters, with relaxin levels approximately three times lower and both oestrogen metabolites roughly half those observed in hotbloods (P < 0.05). Given relaxin's critical role in cervical remodelling and myometrial compliance before parturition, the markedly depressed relaxin concentrations in coldblooded breeds warrant investigation as a potential physiological contributor to the documented higher incidence of dystokia and obstetric intervention in these populations. Veterinary practitioners should exercise caution when applying hotblood reference ranges to coldblooded mares; breed-specific hormone baselines may improve risk stratification for pregnancies requiring closer monitoring or planned intervention in the final gestation period.
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Practical Takeaways
- •Coldblooded mares carrying pregnancies in the second half of gestation have markedly different hormone profiles than hotblood mares—reference ranges must be breed-specific to avoid misinterpretation of pregnancy risk
- •The substantially reduced relaxin levels in coldblooded mares may explain the higher dystocia rates observed in draft and coldblooded breeds; this could inform periparturient monitoring and intervention protocols
- •Practitioners should not apply hotblood mare reproductive hormone reference values to coldblooded mares for pregnancy assessment or risk stratification
Key Findings
- •Serum relaxin concentration was approximately 3-fold lower in coldblooded mares compared to hotblood mares during late gestation (P < 0.05)
- •Estrone sulphate (E1S) and estradiol-17β (E2) concentrations were approximately 2-fold lower in coldblooded mares compared to hotblood mares (P < 0.05)
- •Significantly lower relaxin levels in coldblooded mares may contribute to the increased incidence of difficult parturition requiring veterinary intervention observed in these breeds