Comparative hematological and serum biochemical profiling of grassland Xichun and Xilingol horses

The Grassland Xichun horse is an emerging crossbred population developed from Xilingol mares and Thoroughbred stallions in Inner Mongolia, China, yet its blood physiological profile has not been systematically characterized. In this study, we compared 32 hematological and serum biochemical parameters between 177 Grassland Xichun horses and 35 Xilingol horses maintained under the same extensive grazing conditions. Following Benjamini-Hochberg FDR correction, 17 of 32 parameters differed significantly between breeds. Grassland Xichun horses showed markedly higher RBC count (9.145 vs 7.905 × 10¹²/L), hemoglobin (155.41 vs 132.51 g/L), hematocrit (45.95% vs 40.29%), and MCHC, with multiple parameters reaching the large-effect threshold (absolute effect size > 0.8). Compared with the Xilingol maternal breed, the Thoroughbred-sired Grassland Xichun population was associated with higher oxygen-carrying indices. Conversely, LDH showed the largest effect size among all parameters (effect size = -2.117), and AST and CK were also lower in Grassland Xichun horses, suggesting differences in basal muscle enzyme profiles and aerobic metabolic characteristics between breeds. Grassland Xichun horses additionally exhibited higher blood glucose and lower total cholesterol, indicating distinct metabolic patterns. Xilingol horses displayed elevated monocyte counts, MPV, UREA, and GGT, which may reflect differences in immune-metabolic status and physiological adaptation associated with long-term environmental and management backgrounds rather than discrete functional phenotypes. Principal component analysis revealed partial breed separation reflecting shared maternal ancestry, and Fisher's linear discriminant analysis achieved 97.6% leave-one-out cross-validation accuracy. This study characterizes the blood physiological profile of Grassland Xichun horses, provides population-level distribution data for clinical interpretation, and supports future integration of hematological phenotypes into breeding evaluation and physiological monitoring programs.