Associations of age and body condition score with automated platelet indices in mares.

Age- and adiposity-related variations in platelet indices have been described in several species, where both factors have been associated with platelet number, size, and other platelet-related characteristics. However, comparable information in mares is scarce, and the associations of age and body condition score (BCS) with automated platelet indices remain poorly defined. This study hypothesized that age and BCS are associated with variations in platelet indices in mares. The objective was to evaluate the associations of age and BCS with platelet count (PLT) and ADVIA-derived platelet indices in Spanish Purebred mares. Forty-five non-pregnant, clinically healthy mares were classified into three age groups (4-8, 9-12, and 13-17 years) and three BCS categories (4-5, 6-7, and 8-9). Platelet indices, including quantitative, size-related, mass-related, heterogeneity, and aggregation parameters, were measured using the ADVIA 2120i analyzer. Data were analyzed using a two-way General Linear Model (GLM) including age group, BCS category, and their interaction (Age × BCS) as fixed effects. Associations between age, BCS, and platelet indices were further evaluated using Spearman's rank correlations. Age was significantly associated with PLT and platelet aggregation (AGREG), whereas no significant main effects of BCS were detected for most platelet indices. However, significant Age × BCS interactions were identified for platelet component distribution width (PCDW), platelet mass distribution width (PMDW), and AGREG, suggesting that the relationship between age, BCS, and these platelet characteristics may depend on the combination of both factors. Correlation analyses mainly identified expected relationships among platelet size-, mass-, and heterogeneity-related indices, whereas PLT showed limited associations with the remaining platelet variables. Overall, platelet quantity remained relatively stable across age and BCS categories, whereas selected platelet heterogeneity and aggregation-related indices appeared more sensitive to the interaction between these factors, highlighting age and BCS as potential sources of biological variation in platelet measurements in mares.