Electrical Stunning of Pigs: Equipment, Current, and Voltage Methods

Pigs are stunned with electric current of elevated or industrial frequency. Before stunning, the animals are secured on special conveyors or by means of other devices, and restraining boxes are also used (Fig. 1).

Stunning pigs with industrial-frequency current is carried out using a stick electrode applied to the occipital part of the animal's head. The floor serves as the second contact. The current voltage is 65–100 V, the frequency is 50 Hz, and the duration of action is 6–8 seconds. Figure 1 – Carousel box for automatic electrical stunning of pigs: 1 – rotating floor; 2 – rotating inner wall; 3 – electrodes for electrical stunning; 4 – pen for pigs; 5 – signal and lighting lamps; 6 – electric motor; 7 – gearbox; 8 – tubular shaft; 9 – FEOS unit; 10 – cut-off device; 11 – roller table; 12 – roller conveyor; 13 – strip overhead track.

At low-capacity enterprises, it is practical to stun pigs with a special needle mounted together with a 24 V current source. The needle is inserted into the muscles behind the ear and is not removed until the food-grade blood has been fully collected. The duration of the process is 45 seconds.

Why does electric current of elevated frequency reduce carcass damage?

At the moment of electrical stunning, pigs experience a rise in blood pressure and convulsive contraction of the muscles, which leads to haemorrhages and worsens the marketable appearance of the meat. To prevent this, pigs are stunned with current of elevated frequency using the FEOS-U4 apparatus, applying a two-pole stick electrode to the area of the post-auricular hollows or the temples. The voltage in the apparatus is 200–250 V, the current frequency is 2400 Hz, and the duration of action is 8–12 seconds. Figure 2 – FEOS unit for electrical stunning of pigs: a – general view of the unit; b – fork of improved design; 1 – tube; 2 – hollow handle; 3 – blocks; 4 – centring screw; 5 – fork.

How is the FEOS electrical stunning unit built?

The FEOS-1 apparatus has a productivity of 50 head per hour, with an electrical stunning duration of 25 seconds. The electrical stunning installation (Fig. 2 a) consists of a control station, a high-frequency unit, and two forks for stunning the pigs. The control station is a metal cabinet that houses the measuring and monitoring instruments and the equipment ensuring normal operation of the installation.

The high-frequency unit is of vertical single-housing design, positioned separately, and consists of a three-phase driving asynchronous electric motor and a generator. The fork is a tube on one end of which two electrodes are fixed on an insulating block; high-frequency voltage for stunning is supplied to them. A four-core cord is inserted into the other end of the tube, terminating in a plug-connector insert by which the fork is connected to the control station.

A switch is located inside the tube; protruding from it, the switch supplies stunning voltage to the fork's electrodes when its key is pressed. The fork of improved design is shown in Fig. 4 b. This fork consists of a lightweight bent tube with a plastic handle and a head that can be fully disassembled by unscrewing the centring screw. A labyrinth seal provides moisture resistance, while the tube's polyvinyl chloride insulation ensures the worker's safety.

Stunning pigs with a gas mixture

Stunning pigs with a gas mixture uses a blend of 65% carbon dioxide and 35% air. The gas-mixture stunning is performed in a sealed chamber for 45 seconds. The animal sinks into a deep sleep and remains in a motionless, relaxed state for 1–2 minutes. During this time it is hoisted onto the overhead track, after which slaughter and bleeding are carried out.

Inclined elevators are used to lift the pigs. Beforehand, a shackle chain is placed on the hind leg in the area of the cannon bone, the resulting loop is tightened, and the chain is attached to a hook.