Electric Stunning of Cattle
By Temple Grandin, PhD
Dept. of Animal Science
Colorado State University
Fort Collins, CO 80523, USA
(Revised January 2020)
Electric stunning of cattle has been successfully used for many years in New Zealand and it is in compliance with strict animal welfare codes. A minimum of 1.2 amps must be passed through the bovine's head for a minimum of 2 seconds. The current must pass through the brain. Commercially available equipment that is used in New Zealand is very effective when it is used correctly. The one possible problem area is the use of electric stunning on dehydrated cattle. Unfortunately the cost of the New Zealand equipment is prohibitive for use in many other countries. Some homemade electric stunning systems are not effective. These systems often consist of a hand held electrode that is held on the head and the current grounds out through the floor of the stun box. These systems are bad for two reasons:
- Cattle are too big to be stunned effectively by a single current passing from the head to the feet. The current may bypass the brain. Even though the heart is stopped by the electrical current, the animal may feel the shock. To induce instant insensibility, the current must enter the brain and cause a grand mal epileptic seizure.
- Another problem is that a hand held electrode applied to the head often fails to maintain contact when the animal falls unless it's head is held in a restraing headholder. This may result in the animal feeling the shock.
- Use of the stun box floor as an electrode is a poor design because the feet may fail to stay in complete contact with the floor for the entire duration of the stun.
An electric stunner for cattle must have the following features to maintain good animal welfare:
- For head only stunning, two electrodes must be applied to the head and held in firm contact with the head when the animal falls. In the New Zealand system the current passes from a neck stanchion to a nose plate. Another alternative would be modification of a chin lift used for religious slaughter. The electrode position would be forehead to chin. Another possible position would be across the head between the eye and the ear, like head only tongs used for pigs. The tong would have to stay attached to the head when the bovine falls. The neck to neck position must NEVER be used because the current may fail to go through the brain. A headholder that holds the animal's head up when the body falls is stronlgy recommended.
- To prevent stress on the animal, the current must be applied immediately after the head electrodes are applied. Head restraint devices that cause 5% or more of the cattle to vocalize (moo or bellow) are not acceptable.
- Water must be applied to the electrode during the stun to reduce electrical resistance. Some systems have failed due to high electrical resistance through the bovine's hair. This is especially a problem in cattle with long hair. Be careful not to apply excessive amounts of water which may cause the current to be diverted over the surface of the animal instead of passing through the brain.
- When head only electrical stunning is used the bovine must be bled within 10 seconds. Head only stunning is often used for Halal slaughter.
- The two stage stun described here has been verified by scientific research. If cardiac arrest stunning is desired to stop the heart, the head stun must be applied first by the two electrodes on the head. After the head stun, a second current can be applied to the body to stop the heart. The design of the cardiac arrest electrode is less critical and a hand held probe would be effective. Hand held probes should NOT be used to apply the initial head stun, unless the animal's head or body is supported to prevent the animal from falling away from the electrode.
- In some plants, to stop kicking after stunning, an immobilizing current is applied to paralyze the muscles. This current is NOT a substitute for an effective head stun. The first step of the process of electric stunning of cattle must be an initial head stun applied by electrodes which will stay in firm contact with the animal's head when it falls. Immobilization of a conscious animal with a weak electric current is highly aversive. Several scientific studies have shown that immobilization of conscious sensible animals is very detrimental to animal welfare.
- When electric stunning is assessed for return to sensibility, immobilization devices must be turned off. The animal may kick. This is a normal sign of a grand mal epileptic seizure. An electric immobilization device will mask the normal tonic (ridgid phase) and clonic (paddling leg movements) of an effective head only electric stun that has induced epileptic activity in the brain. Head only stunning that is reversible is often used in Halal slaughter plants. When cardiac arrest stunning is used, the tonic and clonic phase of the epileptic seizure will be partially blocked by the heart stopping current.
- For the initial head stun, an electrical frequency of 50 to 60 Hz is most effective.
- Observations in a slaughter plant indicate that a single electrical current passed from the forehead to the side of the body may be effective. The tonic and clonic spasms of a grand mal epileptic seizure were induced by using this position. The body electrode should be isolated from a steel restraining device.
- To safely wet the electrodes during the stun, a small stream of water should be applied continuously during the stun. This must NOT be applied by a person holding a hose. It must be applied by a separate pipe system that is NOT touched by people during stunning.
- Electric stunning is much more likely to fail and not produce insensibility in dehydrated cattle. I have observed this problem in three different plants. Even though the New Zealand electric stunner was working perfectly, many animals showed signs of return to sensibility such as blinking and rhythmic breathing. Problems with dehydrated cattle are most likely to occur in cattle that have been trasported long distances. Some animals that have been drinking from ponds or large tanks may refuse to drink from small water troughs with an automatic float. They are afraid of the "shsh" sound when the trough refills, and may refuse to drink in the lairage at the plant.
Useful Scientific References
AVMA. 2016. Guidelines for humane slaughter of animals, 2016 edition. American Veterinary Medical Association.
Cook, C.J., Devine, C.E., and Gilbert, K.V., 1991. Electroencephalograms and electrocardiograms in young bulls following upper vertebrae to brisket stunning. New Zealand Veterinary Journal. 39: 121-125.
- - Positioning the electrodes neck to brisket fails to induce epileptic seizure.
Gregory, N.G., 1993. Slaughter technology electrical stunning in large cattle. Meat Focus. January, pp. 32-36.
Gregory, N.G., 2001. Profiles of currents during electric stunning. Australian Veterinary Journal. 79:844-845.
- - Even though this paper is about pigs and sheep, it will provide useful information on determining whether or not the head electrodes are staying in good electrical contact with the head.
HSA. (No Date). head to body stun kill. Humane Slaughter Association, UK.
Sabow, A.B., et al. 2018. Electroencephalographer and blood parameter changes in anesthetised goats subjected to slaughter without stunning and slaughter following different electrical stunning methods. Animal Production Science. 59: 849-860.
Sabow, A.B., Nakyinsige, K., et al. 2017. High frequency electrical stunning in ruminants and poultry for halal meat production. Livestock Scienct. 202:124-134.)
Weaver, A.L. and Wotton, S.B. 2008. The Jarvis Beef Stunner: Effects of a prototype chest electrode. Meat Science. 81:51-56.
Wotton, S.B., Gregory, N.G., Whittington, P.E., and Parkman, I.D., 2000. Electrical stunning of cattle. Veterinary Record. 147:681-684.
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