Repeated intravenous dexamethasone administration causes transient changes in leukocyte parameters in healthy warmblood horses.

Recognize dexamethasone-induced stress leukograms in horses to avoid misinterpretation of glucocorticoid-related hematologic changes.

This prospective, longitudinal study investigated the hematologic effects of repeated intravenous dexamethasone administration (0.06 mg/kg q24h, twice) in five healthy adult warmblood mares. Blood samples were collected at ten time points over 168 hours, and white blood cell parameters were analyzed using linear mixed-effects models. Results demonstrated a consistent and predictable glucocorticoid-induced leukogram pattern. Leukocyte counts, neutrophil counts, and neutrophil-to-lymphocyte ratios peaked at 6 hours post-injection, with mean leukocyte counts exceeding the reference interval, though individual variation was noted. Neutrophilia was universally observed across all horses. Conversely, lymphocyte, monocyte, and eosinophil counts were significantly decreased at 6 hours, with complete eosinophil suppression. The myeloperoxidase index (MPXI) increased only after the second dexamethasone injection, while Neut-X (a measure of neutrophil lobularity/complexity) decreased at 12 hours post-injection and Neut-Y (neutrophil size) remained unchanged throughout the study period. The majority of altered parameters returned to baseline values between 48 and 72 hours following initial administration. This study provides clinically relevant reference data for interpreting hematologic findings in horses receiving glucocorticoid therapy, emphasizing that the characteristic leukogram changes—particularly the stress leukogram pattern of neutrophilia with lymphopenia, monocytopenia, and eosinopenia—should be recognized as pharmacologically induced rather than indicative of concurrent pathology.

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