Retrospective Evaluation of Neutrophil‐to‐Lymphocyte Ratio in Horses That Required Emergency Laparotomy: 341 Cases of Noninfectious Causes of Gastrointestinal Colic (2019–2024)

ABSTRACT Objective To (1) compare total nucleated cell count (TNCC) and neutrophil‐to‐lymphocyte ratio (NLR) at admission between horses with medically managed, large intestinal (LI) and small intestinal (SI) surgical colic; (2) compare TNCC and NLR between survivors and nonsurvivors; and (3) investigate associations between TNCC, NLR, surgical intervention, and outcome. Design Case–control study. Setting Single, academic institution. Animals A total of 341 adult horses diagnosed with noninfectious medical or surgical colic. Measurements and Main Results Admission TNCC did not differ between the medical and combined surgical groups, but NLR was higher in the surgical group (3.3 [2–5.2]) compared to the medical group (2.2 [1.6–3.4]). There was no difference in TNCC among the medical, LI, and SI groups, but the SI group's NLR (3.9 [2.8–6.3]) was higher compared to the medical (2.2 [1.6–3.4]) and LI (3.2 [1.6–4.8]) groups. TNCC was not different between survivors and nonsurvivors, but admission NLR was higher in nonsurvivors (3.6 [2–4.8]) compared to survivors (2.7 [1.7–4]). There was no association between admission TNCC and surgical intervention or outcome, but associations were found between NLR and both the need for surgical intervention and outcome. Conclusions NLR, but not TNCC, at admission is increased in horses with surgical intestinal lesions. Overlap in data precludes its use as a sole marker for case identification, and interpretation of NLR should therefore be performed considering appropriate clinical context. Prospective studies accounting for measurement of adrenocortical hormones are required to investigate NLR changes during the stress response in horses presenting with colic.