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Estrous cycle-dependent changes in platelet indices in healthy mares.
Abstract: Platelets (PLTs) are key regulators of hemostasis, inflammation, and tissue remodeling, and their phenotype is known to fluctuate with sex steroid concentrations in several species. However, the influence of the estrous cycle on PLT characteristics in mares has not been investigated. We hypothesized that PLT indices vary between reproductive phases in association with changes in estradiol-17β (E2) and progesterone (P4). The aim of this study was to characterize PLT indices in estrus and diestrus and to determine how these hematological parameters relate to circulating E2 and P4 concentrations. PLT indices were evaluated in 25 healthy cyclic mares sampled during estrus (Day 0) and diestrus (Day + 12), and their associations with circulating ovarian steroids were assessed. Quantitative parameters (PLT count, plateletcrit [PCT], mean platelet volume [MPV], large platelets [PLCR], and platelet clumps [AGREG]) and qualitative indices of PLT size and heterogeneity-related indices (platelet distribution width [PDW], mean platelet mass [MPM], platelet component distribution width [PCDW], and platelet mass distribution width [PMDW]) were measured using an ADVIA 2120i analyzer. Plasma E2 and P4 were quantified by ELISA and RIA. PLT count, PCT, MPM and MPC did not differ between phases. MPV, PLCR, AGREG, and heterogeneity-related indices (PDW, PCDW, PMDW) were significantly highest during diestrus (P < 0.05), indicating a larger and more variable PLT population. Both hormones showed positive correlations with indices of PLT size and heterogeneity, particularly P4 (P < 0.05). In conclusion, PLT indices in mares vary across the estrous cycle in parallel with ovarian steroid fluctuations.
© 2026. The Author(s), under exclusive licence to Springer Nature B.V.
Publication Date: 2026-06-06 PubMed ID: 42250016PubMed Central: 8070911DOI: 10.1007/s11259-026-11333-xGoogle Scholar: Lookup The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
- Journal Article
Summary
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Overview
- This study investigated how platelet characteristics in healthy mares change during different phases of the estrous cycle and how these changes relate to hormone levels, specifically estradiol-17β (E2) and progesterone (P4).
Introduction
- Platelets (PLTs) play a critical role in blood clotting, inflammation, and tissue repair.
- Previous research in various species shows that platelet features can fluctuate with changes in sex hormone levels.
- However, the specific influence of the estrous cycle on platelet indices in mares had not been explored prior to this study.
- The researchers hypothesized that platelet indices change between estrus and diestrus phases, potentially related to circulating E2 and P4 levels.
Objectives
- To characterize platelet indices during estrus and diestrus in healthy mares.
- To investigate the relationship between platelet parameters and the levels of ovarian steroids E2 and P4.
Methods
- Subjects: 25 healthy cyclic mares.
- Sampling: Blood samples were taken during two phases of the estrous cycle:
- Estrus (Day 0)
- Diestrus (Day +12)
- Platelet evaluation:
- Quantitative platelet parameters measured included:
- Platelet count
- Plateletcrit (PCT) – percentage of blood volume occupied by platelets
- Mean platelet volume (MPV) – average size of platelets
- Large platelet proportion (PLCR)
- Platelet clumps (AGREG)
- Qualitative platelet indices (size and heterogeneity) included:
- Platelet distribution width (PDW)
- Mean platelet mass (MPM)
- Platelet component distribution width (PCDW)
- Platelet mass distribution width (PMDW)
- Measurements were obtained using an ADVIA 2120i hematology analyzer.
- Quantitative platelet parameters measured included:
- Hormone quantification:
- Plasma levels of E2 measured by ELISA
- Plasma levels of P4 measured by RIA (radioimmunoassay)
Results
- No significant differences between estrus and diestrus for:
- Platelet count
- Plateletcrit (PCT)
- Mean platelet mass (MPM)
- Mean platelet component (MPC)
- Significantly higher values during diestrus for:
- Mean platelet volume (MPV)
- Proportion of large platelets (PLCR)
- Platelet clumps (AGREG)
- Heterogeneity-related indices (PDW, PCDW, PMDW)
- This indicates that during diestrus, platelets tend to be larger and more heterogeneous in size.
- Positive correlations were found between both E2 and P4 levels and the indices of platelet size and heterogeneity; progesterone (P4) showed particularly strong correlations.
Discussion and Conclusion
- Findings demonstrate that platelet properties in mares vary over the estrous cycle alongside fluctuating ovarian hormone levels.
- The increase in platelet size and variation during diestrus suggests hormonal modulation of platelet populations.
- Progesterone, which rises during diestrus, appears to have a notable influence on platelet characteristics.
- This study contributes to understanding the physiological variability of platelets in mares and highlights the importance of considering estrous cycle phases when interpreting platelet-related blood parameters.
Cite This Article
APA
Satué K, Fazio E, Colomer-Selva R, Gímenez ED, Cravana C, Fauci D.
(2026).
Estrous cycle-dependent changes in platelet indices in healthy mares.
Vet Res Commun, 50(5), 377.
https://doi.org/10.1007/s11259-026-11333-x Publication
Researcher Affiliations
- Department of Animal Medicine and Surgery, Faculty of Veterinary Medicine, CEU- Cardenal Herrera University, Tirant lo Blanc, 7, Alfara del Patriarca, Valencia, 46115, Spain.
- Department of Veterinary Sciences, Veterinary Physiology Unit, Polo Universitario Annunziata, Via Palatucci 13, Messina, 98168, Italy.
- Department of Animal Medicine and Surgery, Faculty of Veterinary Medicine, CEU- Cardenal Herrera University, Tirant lo Blanc, 7, Alfara del Patriarca, Valencia, 46115, Spain.
- Department of Animal Medicine and Surgery, Faculty of Veterinary Medicine, CEU- Cardenal Herrera University, Tirant lo Blanc, 7, Alfara del Patriarca, Valencia, 46115, Spain.
- Department of Veterinary Sciences, Veterinary Physiology Unit, Polo Universitario Annunziata, Via Palatucci 13, Messina, 98168, Italy.
- Department of Veterinary Sciences, Veterinary Physiology Unit, Polo Universitario Annunziata, Via Palatucci 13, Messina, 98168, Italy. deblafauci@unime.it.
MeSH Terms
- Animals
- Female
- Horses / blood
- Horses / physiology
- Blood Platelets / physiology
- Estrous Cycle / blood
- Estrous Cycle / physiology
- Estradiol / blood
- Progesterone / blood
- Platelet Count / veterinary
Conflict of Interest Statement
Declarations. Ethics approval: All methods and procedures used in the present study followed the guidelines of Spanish law (RD 37/2014) that regulates the protection of animals used for scientific purposes. The Animal Ethics Committee for the Care and Use of Animals of the CEU-Cardenal Herrera University (Spain) concluded that the proposed study did not need ethical approval, since this experiment was part of the clinical evaluation of the animals at this stage of their cycle. Informed consent: Informed consent was obtained from the owners of all subjects involved in the study. Competing interests: The authors declare no competing interests.
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