Some aspects of the effectiveness of stunning in sheep by the captive bolt

Abstract

The effects of penetration depth and the velocity of the bolt on the onset of unconsciousness was investigated in twenty-four sheep of about 45 kg liveweight. The sheeps' state of consciousness was judged from the electrocorticograms recorded via electrodes surgically pre-implanted frontally on the right side of the head. Sixteen sheep were trephined. A commercial captive bolt pistol and an experimental manual bolt, both with variable penetration depths, were used to represent high and low velocity stunning. Stunning by destroying only the cortex or by only penetrating the skull when the experimental bolt or captive bolt pistol, respectively, were used, did not produce unconsciousness. Unconsciousness was obtained after destroying the cortex and deeper parts of the brain with the experimental bolt (low velocity) or after destroying the cortex (and deeper parts of the brain by shockwaves) when using a captive bolt pistol (high velocity). To produce unconsciousness the captive bolt should have sufficient energy and length after penetration of the skull to crush the cortex and deeper parts of the brain, either directly or by shockwaves.