LAB 1.1 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, although concusssion is the most widely used method.  Hand-operated captive-bolt pistols with a .22 blank cartridge are common, but pneumatic concusssion systems or electrical stunning may be used in very large abattoirs.

3. Exsanguination (sticking or bleeding).  While unconscious, a sticking knife is used to open the thick hide at the base of the animal's neck. A second knife is used (the first is now dirty) to penetrate the clean tissues under the hide and to sever the major blood vessels from the heart to the head.  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. Skinning (removal of hide).  Most beef hides are used for leather production. Thus, they are valuable and must not be damaged by cuts as the hide is removed from the carcass.   Cuts are made along the medial (inside) faces of the limbs and along the animal's belly to facilitate the removal of whole hides with as little loss as possible. The apparatus used varies with the size of the abattoir. Large abattoirs will have a hide puller which pulls off the whole hide (like skinning a rabbit). Small abattoirs  may use an air knife (two counter-oscillating circular blades) which reduce the risk of cutting through the hide. At a local level, a skinning knife may be used - but  this will be a lengthy operation.

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 udder or penis are first to be removed, togther with any cod fat in the region between the animal's hindlimbs. 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 rumen 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. Washing frequenctly includes a rinse with fluids such as lactic acid which have antibacterial properties.

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). Dspite the importance of reducing meat spoilage, the carcass must not be cooled too rapidly or else the muscles will shorten (COLD SHORTENING) and the meat will become very tough.  The rule of thumb for beef is not to get below 10 C within 10 hours of slaughter.


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.