Hematologic, prostaglandin F2α-metabolite, serum amyloid A, and serum iron changes in horses with experimentally induced endotoxemia

Background Endotoxemia is a common and severe disease of horses. Most previous studies have monitored changes caused by a bolus dose of endotoxin over short time periods. Objectives We aimed to describe inflammatory responses to endotoxin with inflammatory and hematologic markers monitored over a longer time than has been performed in the past using more prolonged endotoxin exposures. Methods Escherichia coliO55:B5 endotoxin was administered as a 6-hour continuous intravenous infusion of lipopolysaccharide (LPS) to eight horses. Blood cell counts, and prostaglandin F-2 alpha-metabolite (PGM), serum amyloid A (SAA), and serum total iron concentrations were monitored for up to 3 or 6 days. Results An immediate and severe decrease in neutrophils and monocytes occurred in all horses, which subsequently changed to a moderate to strong neutrophilia and monocytosis that persisted for more than 78 hours postinfusion (PI) of LPS. Lymphocyte and eosinophil numbers decreased gradually and then normalized after 66- and 78-hours PI, respectively. Mild to moderate, biphasic thrombocytopenia occurred. A pronounced, transient increase in PGM occurred between 1 and 7 hours, peaking at 2 hours. Serum amyloid A began to increase after 6 hours PI and remained elevated after 72 hours PI. Serum iron was decreased between 6 and 48 hours. The clinical signs were most prominent during the first 24 hours PI and subsided within 48 hours PI. Conclusions Neutrophilia, monocytoses, and high SAA concentrations were present in horses even after the clinical signs had subsided. Serum iron normalized before SAA. Knowledge of these findings is imperative when interpreting laboratory results in horses with possible endotoxin exposure.