Different types of electrical stunning systems

DIFFERENT TYPES OF ELECTRICAL STUNNING SYSTEMS

Low voltage electrical stunning

  • The voltage used is 75 volts.
  • The time of application not less than 7 seconds
  • In order to create a better contact, the electrodes are immersed in a saline solution before use or possess in-built water jets.
  • Since some doubt exists about the overall effectiveness of low-voltage stunning and the length of time for which it should be applied, more use is currently being made of high-voltage systems.

High voltage electrical stunning

  • The voltage used is 300 volts or more and the application time must be atleast 2 seconds and usually 2-3 seconds.
  • This system uses automatic restraints to ensure operators safety.
  • Fractures (vertebrae and scapula) may occur in pigs stunned on the floor.
  • High voltage electrical systems are available in a fully automatic form, which incorporates two V-shaped restrainer-conveyors.
  • These are placed in series and move at different speeds so that the pigs are separated sufficiently to present their heads for stunning to a set of specially shaped electrodes suspended on hinged metal plates which hang down inside the second conveyer and contact the animal’s head as it passes through.
  • The stunning voltage is of the order 600-1000 V.
  • Ninety per cent of the pigs are killed; the remaining 10% are only stunned.
  • Difficulties may be encountered with this system in maintaining a consistently correct positioning of the electrodes across the brain of the pig.
  • It is particularly important that a back-up stunner is always present to deal with any animal, which suffers poor positioning of the electrodes, resulting in only partial stunning.

Head to back or leg stunning

  • Current is applied simultaneously to the head and the back or leg.
  • High-voltage electrical stunning in addition to being used for head-only application, may incorporate special tongs through which current is applied simultaneously to the head and back/leg.
  • In this system the brain is anaesthetized and the heart put into arrest, thus cutting off the blood supply to the brain, which suffers death before the anaesthesia ends.
  • Research work carried out at the Meat Research Institute in Bristol, UK, has shown that brain function ceased 23s after this system of stunning, whereas this time was extended to some 50s with head-only stunning.
  • The animal is killed, thus improving animal welfare and making the stunning-to-sticking interval less important.
  • Sticking is to be performed intrathoracically within 3 minutes for  satisfactory bleeding.
  • A minimum current recommended for pigs is 1.3A applied with a minimum of 250 V  and for lambs  1.0A at 375 V.
  • In order to be fully effective, head-to-back/leg stunning must be combined with automatic restraining systems which prevent adverse reflex muscular movements and the possibility of fractures besides making the task of shackling and bleeding easier for operatives.
  • ‘Pelt-burn’ in sheep occasionally occurs on the back with this method.
  • Whatever type of electrical stunning is used, a back-up stunner, in the form of portable captive bolt pistol should be available for use, not only in incorrectly stunned animals, but also for casualty animals in their transport vehicle or in the lairage.
  • It may be advisable to have an additional set of stunning tongs for use in several electrical sockets positioned throughout the lairage and casualty accommodation.
  • This is particularly useful if sows and boars, which are difficult to stun effectively with a captive bolt, are to be slaughtered.

High-voltage head-to-brisket system

  • This system operates in New Zealand for religious slaughter.
  • Electrodes are applied to the animal in a purpose-built stunning pen following capture in a neck yoke.
  • On capture, a chin lift operates from which a nose contact plate is applied.
  • A current of 2.5 A (at 550 V) is applied between the nose and neck yoke for 3 s to stun the animal, with an additional current applied between the neck and a brisket electrode to produce cardiac arrest.

Head-only system

  • For Head-only electrical systems, a minimum electric current of 400 mA for pigs and 250 mA for sheep and lambs has been recommended to produce an effective stun when the electrodes are placed in the ideal position.
  • However, most experts set their recommendations considerably higher at 1.3A for sheep. 0.6A for lambs, 1A for pigs and 1.5 A for cattle, having made the assumption that tong placement on the head would frequently be far from ideal.

High-pressure water jet combined with electro immobilization

  • A high pressure water jet (pressure of 3900 bar) applied via tubes to a fixed nozzle which was positioned frontally about 2 cm from the skin of the head and had an output opening of 1.0mm.
  • During operation, 2 ml water is injected within 50ms for use in stunning slaughter animals has been in development for a few years.
  • A disadvantage is the occurrence of convulsions immediately after stunning.
  • The convulsions cause danger to the operator and can prevent proper bleeding.
  • To overcome the inexitable occurrence of convulsions the stunning method is combined with an immobilizing electric current.
Last modified: Wednesday, 15 September 2010, 9:22 AM