Physiological Effects of Percussive Stunning

When a sharp, heavy blow is correctly applied to the skull it produces a rapid acceleration of the head, causing the brain to impact against the inside of the skull. There is disruption of normal electrical activity resulting from sudden, massive increase in intra-cranial pressure, followed by an equally sudden drop in pressure. The consequent damage to the nerves and blood vessels causes brain dysfunction and/or destruction, and impaired blood circulation. The duration of insensibility depends on the severity of damage to the nervous tissue and the degree to which the blood supply is reduced. In addition, there may be physical damage to the skull or brain according to the type of stunner used, i.e. penetrative or non-penetrative.

The initial effect on the animal is immediate unconsciousness accompanied by what is known as ‘tonic’ activity. The animal collapses, stops breathing and becomes rigid, with its head extended and its hind legs flexed towards the abdomen. This period of rigidity normally lasts for 10 to 20 seconds following stunning. The forelegs may be flexed initially and then gradually straighten out. However, this depends on the species and the severity of the blow. This tonic activity is followed by a period of involuntary kicking movements which gradually subside. If an animal immediately shows paddling or kicking movements on collapse, it is almost certain that it has not been effectively stunned and it should be re-stunned immediately.

An effective stun can be defined as one which renders the animal immediately unconscious and insensible to pain. The animal collapses, exhibiting exaggerated tonic activity followed by gradual relaxation and involuntary kicking movements. Once the animal is stunned it must be bled or pithed without delay.

The Physical Signs of an Effective Stun are:

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