Concentrations of sulphated estrone, estradiol and dehydroepiandrosterone measured by mass spectrometry in pregnant mares

E. L. Legacki, E. L. Scholtz, B. A. Ball, A. Esteller-Vico, S. D. Stanley, A. J. Conley

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


Background: Few studies have provided a longitudinal analysis of systemic concentrations of conjugated oestrogens (and androgens) throughout pregnancy in mares, and those only using immunoassay. The use of liquid chromatography tandem mass spectrometry (LC-MS/MS) will provide more accurate concentrations of circulating conjugated steroids. Objectives: To characterise circulating concentrations of individual conjugated steroids throughout equine gestation by using LC-MS/MS. Study design: Longitudinal study and comparison of pregnant mares treated with vehicle or letrozole in late gestation. Methods: Sulphated oestrogens and androgens were measured in mares throughout gestation and mares in late gestation (8–11 months) treated with vehicle or letrozole to inhibit oestrogen synthesis in late gestation. An analytical method was developed using LC-MS/MS to evaluate sulphated estrone, estradiol, testosterone and dehydroepiandrosterone (DHEAS) during equine gestation. Results: Estrone sulphate concentrations peaked by week 26 at almost 60 μg/mL, 50-fold higher than have been reported in studies using immunoassays. An increase in DHEAS was detected from 7 to 9 weeks of gestation, but concentrations remained consistently low (if detected) for the remainder of gestation and testosterone sulphate was undetectable at any stage. Estradiol sulphate concentrations were highly correlated with estrone sulphate but were a fraction of their level. Concentrations of both oestrogen sulphates decreased from their peak to parturition. Letrozole inhibited estrone and estradiol sulphate concentrations at 9.25 and 10.5 months of gestation but, no increase in DHEAS was observed. Main limitations: Limited number of mares sampled and available for analysis, lack of analysis of 5α-reduced and B-ring unsaturated steroids due to lack of available standards. Conclusions: Dependent on methods of extraction and chromatography, and the specificity of primary antisera, immunoassays may underestimate oestrogen conjugate concentrations in blood from pregnant mares and may detect androgen conjugates (neither testosterone sulphate nor DHEAS were detected here by LC-MS/MS) that probably peak coincident with oestrogen conjugates between 6 and 7 months of equine gestation.

Original languageEnglish
Pages (from-to)802-808
Number of pages7
JournalEquine Veterinary Journal
Issue number6
StatePublished - Nov 1 2019

Bibliographical note

Funding Information:
We express our gratitude to the technical staff at the Equine Analytical Chemistry Laboratory, School of Veterinary Medicine, University of California, Davis, especially the support of Dr Ben Moeller, Dr Heather Knych, Daniel McKemie, Teresa Bowers, Dr Go Sugiarto and Sandy Yim, who provided expertise, technical support and guidance for analysis of samples by liquid chromatography tandem mass spectroscopy. We also wish to thank Dr Kirsten Scoggin and Michelle Wynn for their assistance with sample collection and Casey Hoffman for her assistance with the estrone sulphate immunoassay validation.

Publisher Copyright:
© 2019 EVJ Ltd


  • androgen
  • horse
  • mass spectrometry
  • oestrogen
  • pregnancy
  • steroid sulphate

ASJC Scopus subject areas

  • Equine


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