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

Background Lactation and parity are physiological factors influencing platelet (PLT) indices, yet their combined effects in mares remain poorly characterized. As a dynamic process, lactation involves metabolic and endocrine changes that may influence thrombopoiesis; therefore, reproductive history and lactation stage may modulate PLT indices. Objective To characterize longitudinal platelet (PLT) indices during early lactation in mares and evaluate the influence of parity on thrombopoietic responses. Methods Fifty-five clinically healthy Spanish Purebred mares were included (20 primiparous and 25 multiparous) and monitored for four months after parturition; an additional group of 10 nulliparous mares was used as control. Blood samples were collected monthly from day 7 postpartum (± 2 days). PLT indices were measured using an ADVIA 2120i analyzer. Data were analyzed using linear mixed-effects models to evaluate the effects of lactation month, parity, and interaction. Results PLT indices showed minimal temporal variation, remaining within physiological ranges. In contrast, parity significantly influenced PLT dynamics. Primiparous and multiparous mares exhibited lower PLT, plateletcrit (PCT), and platelet mass distribution width (PMDW) than nulliparous mares, with differences in mean platelet volume (MPV), large platelets (P-LCR), and platelet clump count (AGREG). Additional differences were observed in platelet distribution width (PDW), platelet component distribution width (PCDW), mean platelet component (MPC), and PMDW across lactation stages ( P < 0.05). Correlations revealed consistent associations among PLT size, mass, and heterogeneity. Conclusions Early lactation establishes a stable hematological state in mares, while parity is primary determinant of PLT phenotype, highlighting the need to consider parity when interpreting PLT indices.