A good stunning method must render an animal unable to experience pain and sensation prior to hoisting and slaughter. The three basic types of stunning methods which are classified as being humane (i.e., pain less) in the United States, Europe and other foreign countries are captive bolt (penetrating and nonpenetrating), electrical, and CO2 (carbon dioxide) gas anesthesia.
The physiological mechanisms of stress are the same before and after the onset of unconsciousness. The release of epinephrine as a result of stress inducers has an effect on the quality of the meat and it is therefore desirable to use a stunning method which produces a minimum of epinephrine secretion.
A literature review indicates the following stunning methods most reliably rendered the animal insensible to pain and minimized detrimental effects to forehead. Cows, steers, heifers, calves - penetrating or nonpenetrating (where brains are being saved) captive bolt or gunshot to the forehead. Shoot behind the poll for heavy Zebu or Brahman cattle only. Market weight pigs (180-250 lb; 80-112 kg.) - electric stunning minimum of 1.25 amps. at 300 to 600 volts with 1 to 3 second application time. Sheep - penetrating captive bolt, gunshot, or electric stunning with sharp pin electrodes or electrodes soaked in brine to insure electrical contact through the wool.
"Mechanical, Electrical and Anesthetic Stunning Methods for Livestock,"
International Journal for the Study of Animal Problems: Vol. 1
, Article 9.
Available at: https://www.wellbeingintlstudiesrepository.org/ijsap/vol1/iss4/9