THE EFFECT OF ELECTRICAL HEAD-ONLY STUN DURATION ON ELECTROENCEPHALOGRAPHIC-MEASURED SEIZURE AND BRAIN AMINO-ACID NEUROTRANSMITTER RELEASE

Effective electrical head-only stunning produces a seizure-like state followed by a period of analgesia seen in animals allowed to recover. Passing of a 1.0 A current (50 Hz, 500 V)for less than 0.2 s, through the head of a sheep does not produce a seizure-like state as evidenced by recorded electroencephalogram. Corresponding to this lack of seizu re-like state, the release of the neurotransmitters glutamate and aspa rtate, in the brain, occurs to levels associated with arousal rather t han seizure. At a duration of 0.2 s, the same stun parameters as above produce a seizure-like state and the release of glutamate and asparta te rises dramatically. The length of the seizure-like state, and the l evels of release of glutamate, aspartate and a third neurotransmitter gamma amino-4-butyric acid (GABA), increased with stun duration until 4.0 s duration, where a peak in these parameters was seen. Stun durati ons of 2.0, 4.0, 8.0 and 12.0 s all produce similar effects. At a dura tion of 20 s, however, the length of the seizure-like state and the re lease of neurotransmitters is less than at shouter stun durations. For welfare purposes a head-only electrical stun, of 1.0 A, at a duration as low as 0.2 s produces unconsciousness and analgesia to subsequent slaughter procedures. However, maximum welfare benefits appear attaina ble at durations between 2.0 and 20.0 s.