Humane Stunning of Cattle and Pigs

by Temple Grandin
Dept. of Animal Science
Colorado State University

(Revised November 2015)

MANY PEOPLE inside and outside the industry misinterpret the leg movements of properly stunned animals. Both veterinarians and ranchers have mistaken reflexes for conscious animals. Properly applied captive bolt and electrical stunning will induce instantaneous unconsciousness.

When a standing animal is stunned with a captive bolt or a firearm it should instantly drop to the floor. In cattle, the neck and legs will contract in a spasm for five to 10 seconds. Hogs will often go into violent convulsions after they are shot. This is a normal reaction indicating the animal is unconscious. Properly stunned cattle in a restrainer conveyor will have a neck spasm, and the head may remain raised for five to 10 seconds. If the spasm lasts longer the animal may be poorly stunned. Cattle stunned correctly will often pull their legs up; however, excessive kicking which makes shackling difficult may be an indication of stunning problems.

After the animal is ejected from the stunning box or restrainer it is normal for the legs to move. The neck should be limp and floppy, and eye reflexes should be absent. If the animal blinks or the eye responds to touch it may still be conscious. Rhythmic breathing and vocalizations must also be absent. If the stunned animals moan, bellow or squeal they are probably still conscious. After captive bolt or gunshot, ALL EYE REFLEXES MUST BE ABSENT.

Cattle and calves should be shot in the forehead. Shooting cattle in the hollow behind the poll should be avoided -- the frontal position is more effective. In sheep, the animal should be shot on the top of the head. Sheep have a thick skull, and shooting in the forehead does not work. Pigs and sows should also be shot in the forehead.

Captive Bolt Maintenance is Essential

Failure to properly maintain a captive bolt gun is the number one cause of poor stunning. A poorly maintained captive bolt will not have sufficient bolt velocity (hitting force) to reliably make an animal unconscious instantly. At the end of each day the captive bolt MUST be taken completely apart and cleaned. Worn bumper rings must be replaced. If a captive bolt is shot only once it still must be completely taken apart and cleaned at the end of each day. It must be treated with the same care as a fine hunting rifle.

Cartridge Quality and Storage

Damp cartridges are anothe rcause of poor stunning and may cause weak shots. Captive bolt cartridges must be stored in a dry place such as an office. Only the number of cartridges used in a single day should be brought to the stunnin garea. If a 22 long rifle is used, it must have quality ammunition. Some cheap ammunition does not have sufficient powder charge. For more information on firearms, see the 2013 AVMA euthanasia guide.

Electrical Stunning

In cattle and pigs, the legs will move, but this should be ignored. Instead, look at the heads -- they should hang straight down and the necks should be floppy. The tongue should hang out and the ears droop down. After electric stunning, gasping and gagging reflexes are permissible, but rhythmic breathing and vocalizations must be absent. The animals must not have an arched back-righting reflex; it should hang straight down. Fully conscious cattle and hogs will arch their backs and bend their heads in an attempt to right themselves. In summary, the head should be "dead." Ignore the body.

When pigs and sheep are properly stunned with electricity, there is an initial spasm during which the carcass will stay still and rigid for 10 to 20 seconds. After this period, kicking will start. Pigs stunned with cardiac arrest equipment will kick less than those stunned with tongs applied to the head.

Almost all large plants use cardiac arrest equipment, and many small locker plants use head-only stunning. Cardiac arrest stunning kills the animal by stopping the heart. Head-only stunning creates a short period of unconsciousness. The animal will revive if bleeding is delayed.

With both types of electrical stunning, sufficient current must pass through the brain to induce a grand mal epileptic seizure. Insufficient current will result in a paralyzed hog which will feel everything. For market weight hogs, a minimum of 1.25 amps is required. Hogs stunned with a lower current may remain conscious. Large pigs weighing over 250lbs (115kg) may require higher amperages. Inducing cardiac arrest requires less current than induction of unconsciousness.

A cardiac arrest stunner that has insufficient current will cause the hog to feel heart attack symptoms. Since cardiac arrest stunning masks the grand mal epileptic seizure, hogs stunned with insufficient current will look the same as hogs stunned with adequate current. To ensure a cardiac arrest stunner is inducing consciousness, a meter must be used to test the amperage. Another method is to look for the rigid (tonic phase) and kicking (clonic phase) of an epileptic seizure.

To pass the electrical current through the brain, one electrode must be placed either on the forehead or in the hollow behind the ear. If the electrode slides too far back on the neck, the hog will be paralyzed, but able to feel the pain. When tong type stunners are used in small plants, both electrodes must be applied to the head. Do not apply them to the neck.

Many small plants use head-only reversible stunning because they lack restraint equipment. Bleeding has to be done quickly before the animal revives. Due to slow hoists, some animals revive prior to bleeding. Plants with this problem either should convert to captive bolt or immediately re-apply the tongs to the chest to stop the heart.

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