Platelet indices’ dynamic in broodmares: Effects of parity and lactation.

Overview

• This study examined how platelet indices in mares change during early lactation and how these changes are influenced by whether the mare is giving birth for the first time (primiparous) or has given birth before (multiparous).
• The researchers found that platelet levels remain stable during early lactation but differ significantly depending on the mare’s parity, suggesting that reproductive history influences platelet characteristics more than the stage of lactation.

Introduction and Background

• Lactation is a complex physiological state involving metabolic and hormonal shifts that may affect blood characteristics, including platelets.
• Platelets (PLT) play a critical role in blood clotting and are measured by various indices including platelet count, volume, mass distribution, and clumping.
• Prior research suggests both lactation and parity (number of births) may influence platelet indices, but their combined effects in mares have not been thoroughly studied.

Research Objectives

• To track changes in platelet indices longitudinally during the first four months after foaling in mares.
• To assess how parity (primiparous vs. multiparous) influences platelet indices in this time period.
• To compare findings to a control group of nulliparous (never given birth) mares to understand baseline platelet phenotypes.

Methods

• Subjects included 55 healthy Spanish Purebred mares divided into:
  • 20 primiparous mares (first foaling)
  • 25 multiparous mares (multiple foalings)
  • 10 nulliparous mares (controls, no foaling history)
• Blood samples were collected monthly starting roughly 7 days postpartum and continuing for 4 months.
• Platelet indices were measured with an ADVIA 2120i hematology analyzer commonly used for detailed blood cell analysis.
• Data analysis employed linear mixed-effects models to account for repeated measures and analyze the effects of:
  • Lactation month (time-postpartum)
  • Parity (number of births)
  • Interaction between lactation stage and parity

Key Findings

• The majority of platelet indices remained consistent throughout early lactation, with values staying within normal physiological ranges.
• Parity had a pronounced effect on platelet characteristics:
  • Primiparous and multiparous mares showed lower platelet count, plateletcrit (PCT, volume occupied by platelets in blood), and platelet mass distribution width (PMDW) compared to nulliparous mares.
  • Differences were evident in other PLT indices such as:
    • Mean platelet volume (MPV) – average size of platelets
    • Large platelet ratio (P-LCR) – proportion of large platelets
    • Platelet clump count (AGREG) – number of aggregated platelets
  • Additional indices including platelet distribution width (PDW), platelet component distribution width (PCDW), mean platelet component (MPC), and PMDW varied across lactation stages (indicating some subtle shifts over time within parity groups).
• Correlational analyses showed consistent relationships among platelet size, mass, and variability, suggesting these indices jointly reflect platelet phenotype.

Interpretation and Implications

• Despite the physiological demands of early lactation, platelet indices are maintained within steady ranges, implying hematological stability in this period for mares.
• Parity emerges as the dominant factor influencing platelet phenotype, suggesting that reproductive history alters thrombopoiesis or platelet turnover.
• Veterinarians and researchers should consider parity status when interpreting platelet-related blood tests in mares, as “normal” reference ranges might differ for nulliparous versus parous individuals.
• The findings contribute to understanding equine reproductive physiology and may inform health monitoring and disease diagnosis involving platelet function in broodmares.

Conclusion

• Early lactation establishes a stable platelet profile in mares, unaffected by time postpartum.
• Parity significantly affects platelet count, size, and distribution, highlighting its importance as a key factor in interpreting platelet indices.
• This study underscores the need to adjust clinical expectations and reference values for platelet measurements based on a mare’s reproductive history.