Blood pressure responses to captive bolt and electrical stunning in sheep and cattle: A systematic review

Cattle and sheep are often slaughtered after electrical stunning or captive bolt stunning utilizing pneumatic or cartridge-driven devices. While the procedure is effective, a percentage of animals regain consciousness after the initial shock. One factor that has not been considered to explain this recovery of consciousness is the effect on systemic arterial blood pressure (BP) - the major determinant of cerebral perfusion. A systematic literature search identified papers measuring BP after captive bolt or electrical stunning. BP increases were observed in all studies except a protocol which used halothane anesthesia, - an agent that lowers BP and antagonizes sympathetic activation-induced increases in BP. The increase in BP is evident within a few sec. The hypertensive response to electrical or captive bolt stunning is consistent with the increases in BP following electrical stunning of pigs, goats, rabbits and cats. Captive bolt stunning is a form of traumatic head injury and hypertension is well known consequence of head injury. Death is less likely to occur if BP is high after traumatic brain injury. The explanation for hypertensive response include stimulation of excitatory centers located in the upper brainstem and damage to inhibitory neurones acting on brainstem/diencephalic centres releasing excitatory spinal cord processes. In conclusion, users of electrical or captive bolt stunning of animals should be aware that the technique can produce a rapid increase in BP that may preserve brain viability and play a role in resumption of consciousness in some animals and has implications for animal welfare.