Etiopathogenesis and Immunological Profiling of Recurrent Post-Surgical Peritonitis in Horses at Equine Referral Centers in Northern Nigeria

Recurrent post-surgical peritonitis in horses following colic laparotomy is associated with high morbidity and mortality and complex immunopathological mechanisms that are not fully characterized in West African equine populations. This doctoral study investigates the etiopathogenesis, immunological biomarker profiles, and clinical predictors of recurrent peritonitis following equine abdominal surgery at equine referral centers in Kano, Kaduna, and Sokoto States, North West and North Central Nigeria, between 2020 and 2024. A prospective case-cohort design enrolled 84 horses undergoing laparotomy for colic, of whom 21 developed confirmed recurrent peritonitis. Peritoneal fluid and serum samples collected at 24, 72, and 168 hours postoperatively were analyzed for proinflammatory cytokines including interleukin-6 and tumor necrosis factor-alpha, serum amyloid A, and peritoneal lactate dehydrogenase activity. Peritoneal microbiome analysis was performed using 16S rRNA amplicon sequencing. Horses developing recurrent peritonitis demonstrated significantly elevated interleukin-6 and serum amyloid A at 24 and 72 hours compared to uncomplicated cases. Disruption of peritoneal microbiome diversity characterized by loss of obligate anaerobic taxa was identified in 86% of recurrent peritonitis horses. Enterococcus faecalis and Klebsiella pneumoniae were the predominant pathogens recovered. A predictive risk score incorporating 24-hour interleukin-6 level, peritoneal lactate dehydrogenase, and initial surgery duration achieved an area under the curve of 0.88 for recurrent peritonitis prediction. These original findings advance the understanding of equine post-surgical peritonitis immunopathology in northern Nigeria and provide the basis for early risk stratification protocols. Keywords: equine peritonitis, immunological profiling, post-surgical complication, microbiome, laparotomy.