Electrical stunning, renders an animal instantly insensible by inducing a grand mal epileptic seizure. Scientific research has shown, that in order to induce the seizure the electric stunner must be set at a minimum of 1.25 amps for market weight pigs and l amp for sheep. Large sows will require 2 or more amps. If’ lower amperages are used the stunner may induce cardiac arrest but the animal will feel the shock because the seizure was not induced. Electrical frequencies up to 800 hz (cycles) can be used. Frequencies over 800 hz should not be used. Research has shown that 1500 cycles failed to induce instant insensibility. Animals that are dehydrated may have high electrical resistance and be difficult to stun.

In some plants, cattle or sheep are immobilized after electric stunning with a small electric current to stop kicking. This immobilizer current completely masks signs of return to sensibility. To assess return to sensibility the immobilizer current MUST be turned off. Electric immobilization is highly distressful to animals and it must never be confused with electric stunning, which induces instantaneous insensibility by passing a high amperage current through the brain.

If an electrically stunned animal blinks within 5 seconds after stunning this is a sign that the amperage is too low. In electrically stunned animals, blinking should be checked within 5 seconds and after 60 seconds. In most plants blinking will not be found immediately after stunning, because the plant is using the correct amperage. After it has been verified that the amperage is set correctly, the most important point to observe for signs of return to sensibility is 60 seconds after electrical stunning. This provides time for the eyes to relax after the epileptic seizure. Checking for signs of return to sensibility after bleeding insures that the animal will not recover.

When stunned animals of all species are viewed from a distance, the most important signs to look for in a properly stunned animal are:

  1. A floppy head. The head should flop like a wet rag when a hind leg kicks due to reflexes.
  2. Tongue hangs straight out and is limp. There are some animals that are stunned properly and the tongue may be trapped in the mouth.
  3. In cattle and pigs, the back and head hang straight down. There is no arched back righting reflex.
  4. Ignore limb movement for all methods of stunning. Look at the head.

Animals that show all three of the above signs will be insensible and blinking and other eye reflexes will be absent.

Order of the events which indicate Return to Sensibility:

  1. Single feeble eye (corneal) reflex in response to touch (probably still insensible and not conscious).
  2. Return of rhythmic breathing, where the ribcage moves in and out two or more times. This is a primary indicator of poor stunning and it may occur before the corneal reflexes.
  3. Spontaneous natural blinking without touching (recommended sign for determining return to sensibility for regulatory purposes). In large plants this is easier to assess than rhythmic breathing.
  4. Response to a painful stimulus such as pricking the nose with a pin. The stimulus must be applied to the head to avoid confusion with spinal reflexes.
  5. Righting reflex and raises it’s head.
  6. Fully conscious and sensible. Complete return to sensibility can occur within 15 to 20 seconds after eye blinks appear if an electrically stunned animal is not bled.

The American Meat Institute guidelines require that ALL of the signs of return to sensibility MUST be absent to pass an audit. Even thought an animal is probably insensible if it shows a weak corneal reflex or tongue movement, it is starting the process of return to sensibility. Weak indicators of return to sensibility can be abolished by improved stunning practices. Slaughter plants are not research laboratories where conditions are carefully controlled. Therefore a much greater margin of safety is required to ensure that the animal remains insensible.

An animal showing any of the above signs must be immediately re-stunned before any slaughter procedures are started.

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