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Reproduction & fertility2025; 6(3); doi: 10.1530/RAF-25-0027

Endocrine profile and OPU-ICSI outcomes in mares: a comparative study.

Abstract: Despite recent improvements in equine ovum pick-up (OPU) combined with intracytoplasmic sperm injection (ICSI), there is still significant inter-individual variability. In this study, serum concentrations of the oocyte-secreted factors growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15), as well as the GDF9/BMP15 complex, anti-Müllerian hormone (AMH), progesterone (P4), and free and conjugated estradiol-17β (E2), were determined in 59 mares (3-24 years) at the time of OPU. Mares were classified retrospectively, based on the number of embryos obtained, into low or high outcome groups, using two or three embryos as the threshold values. Results of OPU-ICSI were not affected by the mare's age, body condition score, cycle stage, number of aspirated follicles, number of recovered oocytes, or the recovery rate (P > 0.05 in all cases). Mares with <2 or ≥2 embryos had similar hormone levels (P > 0.05 in all cases), but there was a >90% likelihood of obtaining ≥2 embryos per session when P4 and E2 concentrations were considered simultaneously. Mares with ≥3 embryos/session had lower P4 and higher AMH (P < 0.05 in both cases). GDF9 and BMP15 were detectable in 14 and 12% of mares, respectively, while the GDF9/BMP15 complex was detected in 93% of mares, with no correlation to other factors. In conclusion, these preliminary findings suggest a negative correlation between high P4 levels and OPU-ICSI outcome in horses. Unassigned: We analyzed the relationship between the hormone profiles of mares at the time of egg collection and the outcome of intracytoplasmic sperm injection (ICSI), as ICSI success often varies significantly between individuals. There were no differences in the hormone profiles of mares producing fewer than two or two or more embryos. However, mares with three or more embryos/session showed significant differences in their hormone profiles compared to those producing fewer than three embryos/session. These changes were mainly related to steroid hormones produced by the ovary, such as progesterone and estradiol, and to the concentration of AMH. Our results suggest a possible influence of the hormone profile of the mare on the number of embryos obtained.
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Publication Date: 2025-07-04 PubMed ID: 40539920PubMed Central: PMC12231760DOI: 10.1530/RAF-25-0027Google Scholar: Lookup
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  • Journal Article
  • Comparative Study

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

This research explores the link between certain hormone levels in horses and the effectiveness of intracytoplasmic sperm injection, a method to treat infertility. The study finds that high levels of the hormones GDF9, BMP15, AMH, progesterone and estradiol-17β may hamper successful pregnancy outcomes.

Introduction to the Study

  • The study was conducted to explore the inter-individual variability in the success rates of equine ovum pick-up (OPU), a fertility procedure, combined with intracytoplasmic sperm injection (ICSI), a technique where individual sperm are injected directly into an egg.
  • The researchers took blood serum measurements from 59 female horses of a variety of ages (3 to 24 years) at the time of the OPU procedure. These measurements included concentrations of several hormones and proteins: the oocyte-secreted factors growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15), the complex of GDF9 and BMP15, anti-Müllerian hormone (AMH), progesterone (P4), and free and conjugated estradiol-17β (E2).

Criteria for Categorizing Study Animals

  • The horses in the study were divided into low and high outcome groups retrospectively. This grouping was based on the number of embryos obtained in each group after performing OPU-ICSI, with the threshold between the groups being two or three embryos.

Research Findings

  • The success rates of the OPU-ICSI procedure wasn’t influenced by the age or body condition score of the horses. Similarly, the number of follicles aspirated, number of oocytes recovered, or the recovery rate did not correlate to the success rates.
  • There was no significant difference across the hormone concentrations of horses that had less than two or equal to or more than two embryos. There was, however, a 90% probability of getting two or more embryos in each session when horses had particular concentrations of progesterone (P4) and estradiol-17β (E2) simultaneously.
  • Horses yielding three or more embryos per session had lower P4 and higher AMH concentrations. Both these observations were statistically significant.
  • GDF9 and BMP15 could be detected only in 14% and 12% of the horses, respectively. Almost all horses (93%) registered a presence of the GDF9/BMP15 complex, but these data appeared unrelated to the other measured factors in the study.

Conclusion of the Study

  • The preliminary results of this study suggested that there’s an inverse relationship between higher levels of progesterone and the success rate of the OPU-ICSI procedure for treating horse infertility. Additional research is required to confirm and further explore this correlation.

Cite This Article

APA
Scarlet D, Schuler G, Malama E, Bollwein H, Bocci C, Colleoni S, Lazzari G, Galli C, Kowalewski MP. (2025). Endocrine profile and OPU-ICSI outcomes in mares: a comparative study. Reprod Fertil, 6(3). https://doi.org/10.1530/RAF-25-0027

Publication

Reproduction & fertility
ISSN: 2633-8386
NlmUniqueID: 101778727
Country: England
Language: English
Volume: 6
Issue: 3

Researcher Affiliations

Scarlet, Dragos
  • Institute of Veterinary Anatomy, Vetsuisse Faculty Zurich, Zurich, Switzerland.
  • Clinic of Reproductive Medicine, Vetsuisse Faculty Zurich, Zurich, Switzerland.
  • AgroVet-Strickhof, Vetsuisse Faculty, Lindau, Switzerland.
Schuler, Gerhard
  • Veterinary Clinic for Reproductive Medicine and Neonatology, Justus-Liebig-University, Giessen, Germany.
Malama, Eleni
  • Clinic of Reproductive Medicine, Vetsuisse Faculty Zurich, Zurich, Switzerland.
  • AgroVet-Strickhof, Vetsuisse Faculty, Lindau, Switzerland.
Bollwein, Heinrich
  • Clinic of Reproductive Medicine, Vetsuisse Faculty Zurich, Zurich, Switzerland.
  • AgroVet-Strickhof, Vetsuisse Faculty, Lindau, Switzerland.
Bocci, Carlotta
  • Avantea, Cremona, Italy.
Colleoni, Silvia
  • Avantea, Cremona, Italy.
Lazzari, Giovanna
  • Avantea, Cremona, Italy.
Galli, Cesare
  • Avantea, Cremona, Italy.
Kowalewski, Mariusz Pawel
  • Institute of Veterinary Anatomy, Vetsuisse Faculty Zurich, Zurich, Switzerland.

MeSH Terms

  • Animals
  • Horses / blood
  • Horses / physiology
  • Sperm Injections, Intracytoplasmic / veterinary
  • Female
  • Estradiol / blood
  • Pregnancy
  • Progesterone / blood
  • Growth Differentiation Factor 9 / blood
  • Anti-Mullerian Hormone / blood
  • Oocyte Retrieval / veterinary
  • Bone Morphogenetic Protein 15 / blood
  • Retrospective Studies
  • Treatment Outcome

Conflict of Interest Statement

The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the work reported.

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Citations

This article has been cited 1 times.
  1. Márquez-Moya A, Carreras-Vico N, Sala-Ayala L, Martínez-Boví R, Cuervo-Arango J. Comparative Evaluation of Follicular Flushing Frequency and Scraping Time During Ovum Pick-Up in Mares: Effects on Oocyte Recovery Rate and Technical Considerations. Reprod Domest Anim 2026 Feb;61(2):e70183.
    doi: 10.1111/rda.70183pubmed: 41674388google scholar: lookup
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