There have been many questions about the best way to determine if animals have been rendered insensible by electric stunning. If the animal has a true natural blink, it is not stunned correctly. A natural blink occurs when the eye makes a complete cycle of opening and closing. To test for a natural blink, wave your hand a few inches from the eye. A natural blink will look like a live animal in the stockyard.
Research clearly shows that electric stunning must induce a grand mal epileptic seizure. Failure to induce a seizure will result in an animal that may be paralyzed and sensible to pain. In many countries, both regulations and guidelines state that a minimum of 1.25 amps must be passed through the brain. The original studies were done on small, 100-kg (220-lb.) pigs. The larger pigs that are being processed today will often require a greater amperage setting.
The best electric stunners use an amperage-regulated circuit. The desired amperage is set and voltage varies. In the US and other countries, there are older, voltage-regulated units being used. In very small US plants, these units are popular because they are much less expensive. With this type of unit, the desired voltage is set and the amperage varies. The question that has been asked is: ‘Are voltage-regulated units humane?’
The bottom line is: regardless of circuit design, an electric stunner must produce an epileptic seizure. I have observed stunners with fake amperage meters. There are also units available that change the frequency of the current to prevent blood-splash damage in the meat. Higher frequencies reduce meat damage, but too high of a frequency will fail to induce a seizure. Since it is impossible for all plant personnel to become electrical engineers, when I audit a plant I look for clinical signs that the stunner is actually creating an epileptic seizure with a tonic (rigid) phase and clonic (kicking, paddling) phase.
When an animal is correctly stunned for one to three seconds with a reversible head-only stun, a clear tonic and clonic phase of the seizure can be observed. If the stunner is held on for 30 seconds, the spine will become depolarized and the seizure will not be observed. This animal will be insensible provided that the stunner was capable of producing a seizure when applied for one to three seconds.
When cardiac arrest stunning is used, the signs of a seizure are difficult to observe. Stopping the heart masks the signs of a seizure. If a sequential stun is used where the current is applied to the head first and then a second current is applied to the heart, it is easy to determine that the stunner is working by delaying the heart stun for a few seconds to observe the tonic and clonic phase. The animal will remain insensible if the heart stun is applied before the clonic (paddling phase) stops. This will solve humane concerns about conducting this test. Failure to do this test would result in thousands of animals that may not be rendered insensible.
In many larger plants, simultaneous head-to-body stunning is used, where a current is passed through both the brain and the heart at the same time. Many of these units use proprietary amperage-regulated and frequency-regulated circuits. In most larger plants, the stunner is applied for two to three seconds. The short time makes it possible to see signs of a weak tonic and clonic phase. The clinical signs of the seizure are partially attenuated (reduced) by body stun. If I can observe a weak rigid and clonic phase, I know the stunner is working and inducing instantaneous insensibility in the animal.
The trend in animal welfare is to use animal-based outcome measures. The OIE and American Meat Institute’s minimum settings are a minimum baseline, but I do not fully trust the meters because I have seen too many fake things. It is also not possible to safely train auditors and inspectors to open up electrical equipment and test it. To ensure humane slaughter, looking at a meter is not sufficient to determine if electrical stunning is creating instantaneous insensibility. An inspector or auditor needs to see signs of a seizure.