Common carotid artery occlusion during slaughter without stunning in cattle: incidence and evidence for physiological significance—a systematic review

Introduction Slaughter by exsanguination via ventral neck incision (SEVNI), as performed in religious slaughter, has been criticized on the grounds that carotid occlusion may impair exsanguination and potentially delay loss of consciousness (LOC), leading to unnecessary pain and distress. The objective of this review is to evaluate the literature specifically addressing the prevalence of carotid occlusions (CO) in SEVNI of cattle and the available evidence for their potential consequences on cerebral perfusion, cortical function, and inferred LOC. Methods A systematic search of PubMed, Google Scholar, Cochrane Library, Medline, and Web of Science identified studies assessing the prevalence and significance of CO in cattle after SEVNI. Non-cattle studies, reviews, commentaries and abstracts without full text were excluded. Studies were independently reviewed by co-authors to minimize risk of bias. Due to heterogeneity in methods and outcomes, results were synthesized narratively. Results Fifteen studies met the inclusion criteria. ROBINS-I framework determined the overall risk of bias to be moderate. Across eligible prevalence cohorts, 13.8% of animals exhibited at least one reported carotid occlusive phenomenon. Conclusions suggesting delayed LOC in animals with CO are primarily inferential and rely on indirect evidence from a small number of studies with methodological limitations. Discussion Based on the available evidence, while CO do appear to occur in a subgroup of animals following SEVNI, there is insufficient evidence to demonstrate that they preserve cerebral perfusion or sustain cortical function at levels sufficient to delay LOC as inferred from available proxy measures. Available physiological and mathematical modeling data instead suggest that cortical perfusion would be expected to fall rapidly after bilateral carotid transection, but these data do not directly measure consciousness. Systematic review registration https://www.crd.york.ac.uk/PROSPERO/view/CRD420261325822 , identifier PROSPERA; (registration number CRD420261325822).