The Slaughter of
Animals
Electrical stunning
• Use of an electrical current passed through the brain.
• Usually, a voltage ranging from 150 to 700 V (AC, 50–60 Hz) is used depending on the system.
• The positioning of the electrodes through which the current is applied is important.
• Head-to-body stunning. In this, current flows both through the brain and between the head and the rest of the body through the heart
• The electrical current flowing through the heart stops it so the animal is killed as well as stunned.
Stunning with gases
• Stunning by exposure to carbon dioxide gas.
• A concentration of 80–90% by volume (in air) is used.
• Because carbon dioxide is heavier than air it can be contained within a pit and the animals lowered into it.
Carbon dioxide works because the carbonic acid
formed when it dissolves in the blood reduces the pH of the cerebrospinal
fluid that surrounds the brain. The acidification disrupts brain
function so the animal loses consciousness when the pH falls below
about 7.1.
• Recently the use of stunning by anoxia has been investigated.
• In this, the stunning occurs through lack of oxygen.
• Unfortunately, the duration of
unconsciousness after removal from the gas is very short, unlike in carbon dioxide
stunning.
Signs of correct stunning using a mechanical device are as follows;
othe animal collapses immediately and does not attempt to stand up
othe body and muscles of the animal become tonic (rigid) immediately after the shot
onormal rhythmic breathing stops
othe eyelid is open with the eyeball facing straight ahead and is not rotated
3. Slaughtering &
Bleeding
• A cut is made at the neck to sever a group of blood vessels including jugular veins.
• The animal is bled by passing slowly over the bleeding trough.
• A process called sticking or exsanguination by the insertion of a knife into the thoracic cavity and severance of the carotid artery and jugular vein.
• This method allows for maximal blood removal from the body.
• On average, brain death occurs between about 15 and 20 s after correct sticking. By this time around 50% of the total blood which will be lost through exsanguination has been removed.
4. Carcass Dressing
• The object of dressing the carcass is to remove the skin, together with the associated hair or feathers, and the gut, and the other non-edible parts of the body, in such a way as to prevent, or reduce to the minimum, contact of the carcass with this dirt.
• The system
operates as a production line with each man
carrying out a single job.
• The dressing of the carcass differs in detail for the different species
• In modern slaughtering systems this has led to the dressing being carried out with the animal hanging by its hind legs from an overhead rail system from the time it has been exsanguinated.
• The forelegs, the head and the tail are removed from the carcass.
• The head is hanged up for inspection.
• In cattle and sheep the oesophagus is sometimes tied or closed with a clip to prevent backflow of the rumen content.
• Next step the carcass is skinned.
• Because of the dangers of contamination of the
surface of the carcass with soil and dirt from the hide or pelt, skinning requires considerable care and skill.
• After the initial cuts with a knife, mechanical hide- pullers may be used to pull the hide or pelt from the carcass.
• Pigs are generally not skinned but the hair is removed by scraping.
• This is facilitated by immersing the pig, after
completion of bleeding, in a tank of water at 60°C for about 5 min (scalding).
• The hot water loosens the hairs and the outer layer of skin, which can then be scraped off.
• Pig carcass also passes through a gas flame which burns off any remaining hair and tightens up the skin.
Evisceration
• To eviscerate the animal a cut is made around the anus allowing the rectum and the rest of the gut to be removed from the abdominal cavity through a ventral incision along the whole length of the
carcass.
• This cut continues through the breastbone
(sternum), allowing access to the thoracic cavity, to the throat.
• The diaphragm is cut round and the trachea
(windpipe), lungs, oesophagus (gullet), heart and liver are removed together as the ‘pluck’
• The carcass is often then split into the two sides by sawing down the backbone.
• Immediately before chilling the carcass may be washed, weighed and graded.
Poultry Processing
• To remove the feathers the birds are scalded, usually at a fairly low temperature (less than 55°C for broilers) for about 30 s.
• The hot water softens the skin so that the feathers are easily pulled out.
• Use of higher temperatures damages the skin and downgrades the appearance of the carcasses.
• Plucking is by rubber-fingered rotating cylinders
• Evisceration is physically separated from the defeathering process to reduce carcass
contamination.
• The skin along the back of the neck is cut and the trachea and crop freed.
• The abdominal cavity is opened up by an incision around the vent (cloaca) to enable the viscera to be pulled out. These include the intestines, gizzard,
liver and heart and reproductive system.
• Poultry processing is now highly mechanized with most operations carried out by machine.
