Further Details of Constant Amperage Hog and Sheep Stunning




In previous blogs it has been discussed that constant amperage stunners are much more effective than voltage regulated stunners in the slaughter of hogs and sheep. 

 Why is that?


The principle of electric stunning is to pass sufficient current through the brain to interrupt its normal activity, so that the animal becomes immediately unconscious and unable to feel pain. When electrodes are applied to the head, the amount of current or amperage that flows will depend on the voltage difference between the electrodes, and the electrical resistance of the animal

The flow of electricity through an object, such as a wire, is known as the current (I) or amperage.

The driving force (electrical pressure) behind the flow of a current is known as the voltage and is measured in volts (V)

The property of a material that limits current flow is known as its resistance (R), the unit of resistance is the ohm (Ω)

The relationship between current, voltage and resistance is expressed by Ohm’s Law. This states that the current flowing in a circuit is directly proportional to the applied voltage and inversely proportional to the resistance of the circuit, provided the temperature remains constant.


    Ohm’s Law: Current (I) = Voltage (V) / Resistance (R)



Animals contain a high proportion of liquid that will conduct electricity well; however, skin, fat, bone, and hair are poor conductors. Electrical current will take the path of least resistance through animal tissue, with the result that only a small proportion of the measured current will penetrate the brain. Animals with heavy fleeces, thick skin, fat layers or thick skulls will have a high electrical resistance. The table below shows how the relationship between current, voltage and resistance differs when stunning sheep of different physical condition when the only parameter that can be regulated is voltage, i.e., a voltage regulated stunner.  In this example, the minimum current required for an effective stun is one amp.



                 Condition of Animal


Dry, Fat and in Full Fleece

Wet, thin, and recently sheared

Voltage Applied (V)

     200 volts

     200 volts

Resistance across head (R)

   1000 Ώ

    150 Ώ

Current (I=V/R)

     0.2 Amps

     1.3 Amps


Ineffective Stun

Effective Stun



The following are all poor conductors and thus have a high electrical resistance:

  • Weight (heavier animals have higher resistance)
  • Fat Thickness (resistance increases with fat thickness)
  • Access to water prior to stunning (more liquid in the animal reduces resistance)
  • Wetness of the skin (wetness decreases resistance)
  • Mineral content of water on the skin (will vary the resistance)
  • Wool or Hair Coat Length (heavier wool and hair increase resistance)
  • Skin Thickness (thicker skin increase resistance)
  • Age (resistance increases with age)

Although we have knowledge of the above variables it is difficult to control them.  Each animal during operation will have a different level of resistance.  Use of a constant amperage regulated stunner that maintains a minimum voltage (or pressure) eliminates these resistance factors.




Electrical Stunning of Red Meat Animal, Humane Slaughter Association, UK, 2013



Maddock, Meatingplace, Stunning technology improvements for pork, 2011

Write a comment

Comments: 0