Multimodal Electrophysiologic and Cerebral Perfusion Assessment of Loss of Consciousness in Calves During Slaughter: A Narrative Review

Background: Determining loss of consciousness during slaughter in calves is fundamentally a neurobiological challenge requiring distinction between cortical awareness and subcortical reflex activity. Electroencephalography (EEG) and evoked potentials directly assess cortical responsiveness, while cerebral blood flow (CBF) constitutes the upstream physiological determinant of cortical viability. Aim: To synthesize current evidence on neurologic effects of slaughter modalities in calves, integrating electrophysiological and cerebral perfusion data within a mechanistic framework relevant to welfare monitoring and policy. Methods: A structured narrative review was conducted following SANRA principles. PubMed/MEDLINE was searched from inception to January 2026 using combinations of terms related to calves, cattle, EEG, evoked potentials, cerebral blood flow, stunning, and exsanguination. Inclusion was limited to peer-reviewed, PubMed-indexed studies reporting neurophysiologic endpoints in cattle or calves. EFSA scientific opinions were consulted for contextual interpretation. Results: Effective penetrating captive bolt and appropriately applied electrical stunning produce cortical lesions compatible with rapid unconsciousness. Exsanguination without prior stunning induces rapidly progressive cerebral hypoperfusion leading to cortical failure typically within seconds, with measurable inter-individual variability. Animal-based measures (ABMs) demonstrate imperfect concordance with cortical endpoints. Integration of EEG with perfusion metrics would provide a physiologically coherent method to distinguish concussive suppression, post-ictal states, and ischemic cortical failure. Conclusions: EEG and evoked potentials remain the strongest markers of cortical unconsciousness in calves. Complementary assessment of CBF can reduce interpretive uncertainty and enhance welfare monitoring precision.