LAB 2.1 Stages of slaughter operation

1. Ante-mortem inspection.  Antemortem means before death - so this is the inspection of the live animal. The inspector will be looking for animals which are crippled and cannot walk properly.  These will be slaughtered separately because they will not be able to negotiate the raceways in the abattoir. The inspector will look for animals with signs of a fever or abnormal behaviour (particularly animals which might have a central nervous system disease). These will be separated and treated specially. For example, this is where outbreaks of very serious diseases like hoof and mouth would first be detected and the panic button activated.

 2. Stunning. The animal must be rendered unconscious before it can be killed by exsanguination (except where there are religoius exemptions). The method of stunning varies considerably. Hand-operated captive-bolt pistols with a .22 blank cartridge are common in small abattoirs, but electrical stunning or carbon dioxide stunning are used in large abattoirs. Electrical stunning uses an alternating current to induce unconsciousness. It may be applied with electrodes  transversely across the head or, alternatively,  longitudinally from the head to the back (anterior to posterior). For carbon dioxide stunning the pigs travel down into a pit (carbon dioxide is much heavier than air) where they become unconscious.

3. Exsanguination (sticking or bleeding).  While unconscious, a sticking knife is used to open the thick skin at the base of the pigs's neck. A second knife is used (the first is now dirty) to penetrate the clean tissues and sever the major blood vessels near the heart. Thus, the puncture wound for pigs is much deeper into the thoracic cavity than for cattle. Care is needed to avoid damaging tissues around the trachea, otherwise blood enters the pleural space and forms clots on the inside of the thoracic cavity.  Care is needed because bacteria may be carried into the animal (veins may have negative pressure) from where the bacteria may rapidly contaminate the meat deep in the carcass.

4. Hair removal.  Although some abattoirs  have a hide puller which pulls off the whole hide (like skinning a rabbit) for use in making pigskin leather (for gloves and hush-puppy shoes), most abattoirs remove the hair but leave the skin on the carcass.  The skin is removed when the carcass is butchered (usually the day after slaughter) and is used for the manufacture of food-grade gelatin.

5. Evisceration (removal of guts). The viscera are removed from posterior to anterior (from the rear of the animal to the front), starting in the abdominal cavity and finsihing in the thoracic cavity.  The mammary glands or penis are first to be removed. This opening then allows removal of the bladder and uterus (if a female), followed by large and small intestines.  Great care is taken in the removal of the anus and rectum, which are first closed off with a plastic bag to prevent faecal contamination of the carcass. Similarly, the oesophagus is tied off at the other end of the gut to prevent contamination of the throat of the carcass. After the intestines, the stomach is removed, followed by the liver and diaphragm. The diaphragm separates abdominal and thoracic cavities and must be cut away from the rib cage. The muscular part of the diaphragm remains on the carcass (it is composed of edible red meat). The lungs, heart and trachea are removed togther - these items are called the "plucks".

6. Post-mortem inspection.  This is a search for parasites, infected lymph nodes and signs of disease in the viscera removed from the carcass. Key components to be inspected are usually spread out on a large tray.

7. Final carcass preparation.   This includes trimming (bruises and tags of inappropriate tissues remaining on the carcass), washing and weighing. Was

8. Chilling.  Meat is NEVER frozen straight off the kill floor, but must be cooled as rapidly as possible to reduce surface bacterial spoilage.  The first meat cooler is around zero degrees centigrade with a high air speed and a high humidity.  It takes all day to cool down a large mass of meat. The day after slaughter, carcasses are moved to a less severe environment (high air speed would dry the carcass too much, while a high humidity would encourage spoilage by surface moulds).  Cold shortening can occur in pork, but is seldom a commercial problem because the pork carcass retains its skin and subcutaneous fat - so cooling is quite slow.
PLAY VIDEO 1
PLAY VIDEO 2

Preparation for slaughter

s108 The optimum amount of rest required by meat animals before they are slaughtered depends on the climate, the distance they have travelled, their method of transport and their general health. In some countries, where animals are auctioned at stock yards before they are taken to an abattoir, the rest periods are sometimes inadequate. This creates a commercial problem that is difficult to evaluate. On one hand, animals lose weight during transport and in holding pens, and it is undesirable to use pens and labour to prolong a rest period that confers no immediately obvious commercial advantage. On the other hand, stressed or weary animals sometimes produce meat with an unacceptable appearance or water holding capacity, and this may create economic losses later on. Animals lose about 0.2% per hour of their live weight once feeding has ceased, but this is very variable. For beef cattle, losses in 48 hours of fasting may range from less than 1% to 8%. About half the live weight loss shows up as a loss in carcass weight. However, improvements may be gained by electrolyte therapy, allowing animals free access to drink electrolytes during lairage.

In some situations, a rest period of one day for cattle and two or three days for pigs is considered to be optimum. However, such rest periods may be counter productive if the animals fight among themselves. Animals are not fed in the 24 hour period prior to slaughter.