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Home / Equine Research Bank / Reprod Domest Anim / GnRH Administration Increases Synchronisation of Ovulation i...
Reproduction in domestic animals = Zuchthygiene2026; 61(1); e70165; doi: 10.1111/rda.70165

GnRH Administration Increases Synchronisation of Ovulation in Mares.

Abstract: The objective of this study was to evaluate the effects of exogenous GnRH administration at the beginning of estrus synchronisation in mares during the spring transitional period. Estrus was synchronised using a progesterone releasing intravaginal device (PRID). The PRID was left in the vagina for 10 days, followed by an injection of 0.4 mg of cloprostenol at PRID removal. The GnRH group (n = 32) was subjected to intramuscular administration of 100 μg of the GnRH agonist triptorelin at PRID insertion, while the control group (n = 32) received 1 mL of sterile physiological saline solution. Ovulation was induced by an intramuscular injection of 3000 IU of human chorionic gonadotropin until the dominant follicle reached a diameter of 35 mm. The mares were examined and insemination was performed. Subsequently, insemination was carried out every 12 h until ovulation. Transrectal palpation and ultrasound were carried out 15 days after ovulation to confirm the presence or absence of an embryonic vesicle. The days of ovulation induction and insemination in the control group were more dispersed than in the GnRH group. Compared with the control group, the time of ovulation induction and insemination in the GnRH group were accelerated and concentrated. In summary, GnRH given at the beginning of the estrus synchronisation program significantly increased synchronisation of ovulation in mares; however, it did not increase pregnancy rates.
© 2026 Wiley‐VCH GmbH. Published by John Wiley & Sons Ltd.
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Publication Date: 2026-01-20 PubMed ID: 41556226DOI: 10.1111/rda.70165Google Scholar: Lookup
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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.

Overview

  • This study investigated whether administering GnRH at the start of estrus synchronization improves the timing and synchronization of ovulation in mares during the spring transitional period.
  • The researchers found that GnRH administration resulted in more synchronized and earlier ovulation, but it did not affect pregnancy rates.

Background and Objective

  • Mares experience transitional periods in spring when reproductive activity resumes, and synchronizing ovulation is important for effective breeding management.
  • Estrus synchronization allows breeders to better plan artificial insemination (AI) and optimize reproductive efficiency.
  • The study aimed to assess effects of exogenous Gonadotropin-Releasing Hormone (GnRH) administration at the beginning of an estrus synchronization protocol on ovulation timing and synchronization in mares.

Methods

  • Animals: 64 mares divided into two groups (32 GnRH treated, 32 controls).
  • Synchronization Protocol:
    • A progesterone releasing intravaginal device (PRID) was inserted and left for 10 days to control the estrous cycle.
    • At PRID removal, mares received 0.4 mg of cloprostenol (a prostaglandin analog) to induce luteolysis and support follicular development.
  • GnRH or Control Treatment:
    • GnRH group received 100 μg of triptorelin (a GnRH agonist) intramuscularly at PRID insertion.
    • Control group received 1 mL of sterile saline as placebo.
  • Ovulation Induction:
    • When the dominant follicle reached ≥ 35 mm diameter, 3000 IU of human chorionic gonadotropin (hCG) was administered intramuscularly to induce ovulation.
  • Monitoring and Insemination:
    • Transrectal palpation and ultrasound examinations tracked follicular development and confirmed ovulation.
    • Artificial insemination was performed initially and every 12 hours until ovulation occurred.
  • Pregnancy Diagnosis:
    • Fifteen days post-ovulation, ultrasound checked for the presence of an embryonic vesicle to confirm pregnancy.

Results

  • The timing of ovulation induction and insemination in the control group was spread over a wider range of days, showing less synchronization.
  • In contrast, the GnRH-treated group showed earlier and more tightly clustered ovulation induction and insemination times, demonstrating enhanced synchronization.
  • Despite more synchronized ovulation, pregnancy rates between the groups did not significantly differ, indicating GnRH did not improve conception success in this protocol.

Conclusions

  • Administering a single dose of GnRH agonist (triptorelin) at the start of progesterone-based estrus synchronization successfully improved the synchronization of ovulation in mares during spring transition.
  • This improved synchronization can help reduce variability in breeding schedules, potentially improving management efficiency.
  • However, enhanced synchronization alone did not translate into higher pregnancy rates, suggesting other factors influence fertility beyond timing of ovulation.
  • Further research may explore combining GnRH with additional reproductive management strategies to improve pregnancy outcomes.

Cite This Article

APA
Cui B, Liu Y, Wu X, Li X. (2026). GnRH Administration Increases Synchronisation of Ovulation in Mares. Reprod Domest Anim, 61(1), e70165. https://doi.org/10.1111/rda.70165

Publication

Reproduction in domestic animals = Zuchthygiene
ISSN: 1439-0531
NlmUniqueID: 9015668
Country: Germany
Language: English
Volume: 61
Issue: 1
Pages: e70165

Researcher Affiliations

Cui, Baoyue
  • College of Animal Science and Technology, Hebei Technology Innovation Center of Cattle and Sheep Embryo, Hebei Agricultural University, Baoding, Hebei, China.
Liu, Yiyong
  • Institute of Xinjiang Yili Animal Science, Yining, Xinjiang, China.
Wu, Xinglong
  • College of Animal Science and Technology, Hebei Technology Innovation Center of Cattle and Sheep Embryo, Hebei Agricultural University, Baoding, Hebei, China.
Li, Xiangyun
  • College of Animal Science and Technology, Hebei Technology Innovation Center of Cattle and Sheep Embryo, Hebei Agricultural University, Baoding, Hebei, China.

MeSH Terms

  • Animals
  • Female
  • Horses / physiology
  • Gonadotropin-Releasing Hormone / administration & dosage
  • Gonadotropin-Releasing Hormone / pharmacology
  • Estrus Synchronization / methods
  • Triptorelin Pamoate / pharmacology
  • Triptorelin Pamoate / administration & dosage
  • Insemination, Artificial / veterinary
  • Ovulation / drug effects
  • Ovulation Induction / veterinary
  • Ovulation Induction / methods
  • Pregnancy
  • Cloprostenol / administration & dosage
  • Cloprostenol / pharmacology
  • Progesterone / administration & dosage

Grant Funding

  • 2024E02020 / Science and Technology Assistance Plan Project for Xinjiang
  • YZ2023A04 / Key Research and Development Program of Ili Kazak Autonomous Prefecture

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