Techniques and hygiene practices in slaughtering and meat handling

EQUIPMENT

Slaughtering equipment, particularly for smaller-scale operations, need not be elaborate and expensive. The amount of equipment will depend on the slaughtering procedures employed. If possible, all equipment should be made of stainless steel or plastic, be rust resistant and easily cleaned and sanitized. Equipment which does not get in contact with the meat (e.g. overhead rails, working platforms, knocking pen) is usually made of galvanized steel.

Basic equipment needed for the slaughtering operation:

• stunning gun, electrical head tongs or simple stunning equipment for direct blow
• knives:
  sticking – 15 cm sharpened on both sides
  skinning – 15 cm curved
• a sharpening steel
• oil or water sharpening stone
• scabbard and belt for holding knives
• meat saw – hand or electric and cleaver
• block and tackle or chain hoist strong enough to hold the weight of the animal to be slaughtered
• pritch, chocks or skinning rack (dressing cradle)
• a strong beam, tripod or track 2.4 to 3.4 m from floor
• spreader – gambrel or metal pipe
• several buckets
• working platforms
• scalding barrel or tank
• pot, barrel or system for boiling water
• bell scrapers
• solid scraping table or platform
• thermometer registering up to 70°C
• hog or hay hook
• torch or flame for singeing

The last seven items indicate additional equipment required when hogs are scalded and scraped rather than skinned.

Useful additional equipment:

• knocking pen
• bleeding hooks (for vertical bleeding)
• blood-catching trough
• wash trough (tripe) Sanitation of hands and tools:
• hand wash-basin
• implement sterilizers

Means should be available to clean thoroughly all equipment coming into contact with carcasses or meat. Implement sterilizers are stainless-steel boxes holding hot (82°C) water, shaped to suit particular equipmentknives, cleavers, saws, etc. (Fig. 2). Knife sterilizers should be placed in positions where every operator who uses a knife has immediate access. Handles as well as blades must be sterilized. Each operator should have at least two knives etc., one to use while the other sterilizes (Figs 10 and 11).

Failure to sterilize all knives and equipment regularly will result in carcass contamination. Bacteria will be transferred from the hide to the carcass and from carcass to carcass (Fig. 12).

TREATMENT OF LIVESTOCK BEFORE SLAUGHTER AND ITS IMPACT ON MEAT QUALITY

Stress in its many forms, e.g. deprivation of water or food, rough handling, exhaustion due to transporting over long distances, mixing of animals reared separately resulting in fighting, is unacceptable from an animal welfare viewpoint and should also be avoided because of its deleterious effects on meat quality. The most serious consequence of stress is death which is not uncommon among pigs transported in poorly ventilated, overcrowded trucks in hot weather. From loading on the farm to the stunning pen animals must be treated kindly, and the lorries, lairages and equipment for livestock handling must be designed to facilitate humane treatment. Stress immediately prior to slaughter, such as fighting or rough handling in the lairage, causes stored glycogen (sugar) to be released into the bloodstream. After slaughter this is broken down in the muscles producing lactic acid. This high level of acidity causes a partial breakdown of the muscle structure causing the meat to be pale, soft and exudative (PSE). This condition is mostly found in pigs.

10. Plastic (right) handles are more hygienic than wooden (left) for knives and other equipment. Note the excessively worn knife (third from left) which should be discarded	12. Poor hygiene during carcass dressing causes the spread of bacteria from the skin of the carcass to knives and to operators’ hands
11. Knives and other equipment should be kept sharp and in good repair

Long-term stress before slaughter such as a prolonged period of fighting during transport and/or lairage leads to exhaustion. The sugars are used up so that less is available to be broken down and less lactic acid is produced.

The reduced acidity leads to an abnormal muscle condition known as dark, firm and dry (DFD) in pigs or dark cutting in beef. The condition is rarer in lamb. Such meat has a high pH (above 6.0) and spoils very quickly as the low acidity favours rapid bacterial growth.

Handling animals during transport and lairage

An electric goad (Fig. 13) should be used rather than a stick or tail-twisting not only to avoid stress but also to prevent carcass bruising. Grabbing sheep by the fleece also causes bruising (Fig. 14).

To avoid fighting, animals not reared together must not be mixed during transport and lairage. Load and unload using shallow stepped ramps to avoid stumbles. Trucks should be neither over- nor underloaded. Overloading causes stress and bruising due to crushing. Underloading results in animals being thrown around and falling more than necessary. Drivers should not corner at excessive speed and must accelerate and decelerate gently.

The lairage should have small pens. Corridors must curve and not bend sharply so that stock can see a way forward. Stock must not be slaughtered in sight of other stock. Plenty of clean water must be available. The lairage must be well lit and ventilated. Do not hold stock in lairage for more than a day. Only fit, healthy stock may be slaughtered for human consumption.

Fasting before slaughter reduces the volume of gut contents and hence bacteria and therefore reduces the risk of contamination of the carcass during dressing. It is usually sufficient for the animals to receive their last feed on the day before slaughter. Stock should have a rest period after arrival at the slaughterhouse. However, long periods in the lairage can lead to DFD if the animals are restless and fighting or mounting.

Animals should be as clean as possible at slaughter. Producers should wash their animals before leaving the farm. Trucks used for transport must be washed after each load and the lairage at the slaughterhouse should be kept clear of faecal matter and frequently washed (Figs 15 and 16).

STUNNING AND BLEEDING OF SLAUGHTER ANIMALS

Stunning prior to bleeding

Most countries have legislation requiring that animals are rendered unconscious (stunned) by a humane method prior to bleeding. Exceptions are made for religions which require that ritual slaughter without prior stunning is practised, provided the slaughter method is humane. Stunning also makes sticking (throat-slitting) less hazardous for the operator. The animal must be unconscious long enough for sticking to be carried out, and for brain death to result from the lack of blood supply.

13. An electric goad delivers a small electric current via two electrodes to encourage animals to move. It avoids stress and carcass damage	15. Trucks must be thoroughly washed after each load
14. Unsightly bruising caused by striking the animal with a stick. This not only causes loss of product but is also inhumane
16. Pens will need washing after emptying

Methods of stunning

Direct blow to skull using a club or poleaxe. The blow must be dealt with precision and force, so that the skull is immediately smashed, causing instantaneous unconsciousness. In cattle the aiming point is in the middle of the forehead in line with the ears, where the skull is thinnest. Horses have thinner skulls and are therefore easier to stun by this method. In sheep and goats the brain is more easily reached from the back of the neck. Pigs have a well-developed frontal cavity so the blow should be aimed slightly above the eyes.

Slaughtering mask. A bolt held in the correct position by the mask is driven into the animal’s brain by a hammer blow. The device is usually fitted with a spring which returns the bolt to its original position.

Free bullet fired from a pistol into the skull is effective but unsafe. This method has been used on horses and cattle.

Captive-bolt pistols fitted with a blank cartridge are effective on cattle and sheep but not pigs whose skulls are thicker (Figs 17 and 18). After firing, the bolt returns to its original position in the pistol. The bolt may or may not be designed to penetrate the skull. With penetrating types the brain becomes contaminated with hair, dirt and bone fragments. If brains are to be saved as edible tissue then the non-penetrating type with a mushroom-shaped head should be used.

Electrical stunning. An electric current of high frequency but, in the case of manually operated equipment, of relatively low voltage (60–80 V) is passed through the brain of an animal for a few seconds to produce unconsciousness. If applied correctly a deep state of unconsciusness is invariably achieved. Strict safety rules must be observed. Head tongs (Fig. 19) are suitable for pigs and sheep but not for cattle. The electrodes carried on the ends of the tongs must be accurately placed (Figs 20 and 21). Places where the skull is thick must be avoided. Electrical contact is impeded by hair and caked mud. Water or brine will improve contact but the head must not be completely wet otherwise the current will have a short-circuit path avoiding the brain. The electrodes must be applied with strong pressure.

	19. Head tongs are used to stun pigs and sheep electrically but are not suitable for cattle. The electrode on the end of each tong is ridged for better contact
17. Captive-bolt stunner suitable for cattle	20. The electrodes must be applied firmly to either side of the head so that the electrical current passes through the brain causing unconsciousness in a few seconds
	21. Head tongs are also suitable for stunning pigs
18. Aiming point for stunning cattle

Carbon dioxide stunning is used only in large pig abattoirs. Pigs are induced into a chamber and exposed to a concentration of 85 percent CO₂ for about 45 seconds. Although effective for anaesthetizing sheep, it is impractical because of large amounts of CO₂ collecting in the wool and affecting operators on the killing line.

Bleeding after stunning

The objectives of bleeding are to kill the animal with minimal damage to the carcass and to remove quickly as much blood as possible as blood is an ideal medium for the growth of bacteria.

Sticking, severing the major arteries of the neck, should immediately follow stunning. Care must be taken not to puncture the chest cavity or it will fill with blood.

22. Immediately following stunning the animal is hoisted by one leg and stuck. For sheep the sticking point is in the side of the neck, the gash cut severing all the major blood vessels in a single movement	23. The sticking point for pigs is in the centre of the neck just in front of the breastbone

Cattle. Insert the sticking knife carefully just above the breastbone at 45° pointed toward the head. Ensure that the carotid arteries and jugular veins are severed in one movement.

Sheep. Draw the knife across the jugular furrow close to the head severing both carotid arteries. Alternatively, the knife may be inserted through the side of the neck, though this requires more skill (Fig. 22).

Pigs. As for cattle but do not go in too far or a pocket of blood will collect at the shoulder (Fig.23). To reduce contamination by the scalding tank water the cut should be as small as possible.

Bleeding on a rail

The most hygienic system of bleeding and dressing is to shackle the animal immediately after stunning, then hoist it on to a moving rail. The animal is stuck while being hoisted to minimize the delay after stunning. Bleeding continues until the blood flow is negligible when carcass dressing should begin without further delay (Fig. 24)

Blood for human use must be collected with special equipment to avoid contamination from the wound, the gullet of the knife. A hollow knife directs blood away from the wound into a covered stainless-steel container without touching the skin or hide. The knife may be connected to a hose to reduce the risk of contamination. The hose may even be connected to a pump to speed the blood flow. Between 40 and 60 percent of the total blood volume will be removed though this will be reduced if sticking is delayed. To prevent coagulation, citric acid solution made up with one part citric acid to two parts water is added at a rate up to 0.2 percent of the blood volume. The main sources of contamination during sticking and bleeding include the knife, the wound and the food-pipe. The knief should be changed after each operation and returned to a sterilizer. Cutting the hide of sheep and cattle and opening out to make a clean entry for the sticking knife reduces contamination from the wound. If the food-pipe is pierced semi-digested food may be regurgitated contaminating the blood and neck wound.

Horizontal bleeding

Horizontal bleeding is claimed to give faster bleeding rates and a greater recovery of blood. This may be due to certain organs and blood vessels being put under pressure when animals are hoisted, thus trapping blood and restricting the flow. Bleeding on the floor is very unhygienic. The operation should take place on a specially designed, easily cleaned stainless-steel table which should be cleaned frequently. If blood is to be saved it must not come in contact with the table before reaching the collecting vessel.

	24. After sticking, the animal should be left to bleed until the blood flow becomes negligible	25. Scalding/dehairing tank which accommodates four pigs: one awaiting immersion, two immersed and one just completing immersion. When the bars are rotated the pigs change position
		26. After immersion any remaining loose hairs are scraped from the skin
27. Simple tank for combined scalding/ dehairing. The tank is filled with water at 60°C, a pig is lowered in, the lid is closed and the paddles rotate, the rubber tips loosening the hairs

Bleeding without stunning

The Jewish and Muslim religions forbid the consumption of meat which was killed by any method other than bleeding. Since it is difficult to guarantee that all animals will recover consciousness after being stunned by any particular method, stunning is not generally allowed. There are exceptions, however. Some communities do accept low-voltage electrical stunning.

Because animals are fully conscious at the time of sticking, ritual slaughter may be less humane than sticking after stunning. To reduce the suffering operators must be highly skilled so that a successful gash cut severing all the veins and arteries is made quickly at the first attempt. Different communities have different regulations as to the orientation of the animal at sticking, some favouring a position lying on its side, others insisting it lie on its back. The animal should not be hoisted until unconsciousness due to lack of blood supply to the brain is complete.

SCALDING AND DEHAIRING OF PIGS (USING SIMPLE EQUIPMENT)

Scalding in water at around 60°C for about six minutes loosens the hair in the follicle. Too low a temperature and the hair will not be loosened and too high a temperature and the skin will be cooked and the hair difficult to remove. The simplest equipment consists of a tank into which the pig is lowered by a hoist. The water is heated by oil, gas, electricity or an open steam-pipe.

To check the effectiveness of the scald, rub the skin with the thumb to see if hair comes away easily. Some machines have the thermostatic controls and timers. To reduce contamination, scalding water should be changed frequently, pigs should be as clean as possible at sticking, and bleeding should be fully completed before immersion.

In large factories pigs are transported through scalding tanks with rotating bars (Fig. 25) or through long scalding tanks stretching from the sticking point to the dehairing point in the time required for an effective scald.

Dehairing is done with a specially formed scraper (bell scraper or knife). If the scald is effective all the hair can be removed by this manual method (Fig. 26). Another simple method is to dip the pig in a bath containing a hot resin adhesive. The pig is removed from the bath and the resin allowed to set partially when it is peeled off pulling the hair with it from the root. This is less labour-intensive than scraping and produces a very clean skin. After use the adhesive is melted again, strained to remove the hair and returned to the tank.

Another method of removing dirt and hair in one operation is to skin the carcass though this is only done when the skin is required for leather goods.

With the simple scalding tank, dehairing and scalding may be combined in one operation. Inside the tank are rotating rubber-tipped paddles which are started after closing the lid. As the hair is loosened by the scalding water it is removed by the rubbing effect of the paddles against the skin (Fig. 27).

Singeing removes any remaining hairs, shrinks and sets the skin, decreases the number of adhering micro-organisms and leaves an attractive clean appearance. It may be done with a hand-held gas torch (Fig. 28). Automated systems transport the pig into a furnace and leave it long enough for an effective singe.

After singeing, black deposits and singed hairs are scraped off (Fig. 29) and the carcass is thoroughly cleaned before evisceration begins.

SKINNING OF CATTLE AND SMALL RUMINANTS

Cattle

The outer side of the hide must never touch the skinned surface of the carcass. Operators must not touch the skinned surface with the hand that was in contact with the skin.

Combined horizontal/vertical methods

Head. After bleeding, while the animal is still hanging from the shackling chain, the horns are removed and the head is skinned. The head is detached by cutting through the neck muscles and the occipital joint. Hang the head on a hook (Fig. 30). Lower the carcass on its back into the dressing cradle.

Legs. Skin and remove the legs at the carpal (foreleg) and tarsal (hind leg) joints. The forelegs should not be skinned or removed before the carcass is lowered on to the dressing cradle or the cut surfaces will be contaminated. The hooves may be left attached to the hide.

28. After scraping away loose hairs any remaining hairs can be singed and the skin set with a hand-held gas torch	30. The head is completely skinned and hung on a hook to await inspection
	29. A special knife, the black scrape, is used to scrape off any singed hairs and black deposits

 

	32. In the combined horizontal/ vertical dressing method the carcass is lowered on to a cradle, the legs, brisket and flanks are skinned, then the carcass is raised to the half-hoist position. Note that this is much less hygienic than verticaldressing on a rail
	33. Note the possible contamination of the carcass by the intestines and the hide dragging on the floor in the combined horizontal/vertical dressing method
31. Correct cutting lines for hide removal

Flaying. Cut the skin along the middle line from the sticking wound to the tail. Using long firm strokes and keeping the knife up to prevent knife cuts on the carcass, skin the brisket and flanks, working backwards toward the round (Fig. 31). Skin udders without puncturing the glandular tissue and remove, leaving the supermammary glands intact and attached to the carcass. At this point raise the carcass to the half-hoist position, the shoulders resting on the cradle and the rump at a good working height (Figs 32 and 33).

Clear the skin carefully from around the vent (anus) avoiding puncturing it and cut the abdominal wall carefully around the rectum. Tie off with twine to seal it. Skin the tail avoiding contamination of the skinned surface with the hide. Raise the carcass free of the floor and finish flaying.

Vertical methods

High-throughput plants have overhead rails which convey the carcass from the sticking point to the chills. Hide removal is carried out on the hanging carcass (Figs 34, 35 and 36). The operations are as in the combined horizontal/vertical method, but as it is not possible to reach the hide from ground level more than one operator is needed. A single operator may work with a hydraulic platform which is raised and lowered as required.

Automatic hide pullers are used in high-throughput slaughterhouses. Some types pull the hide down from the hind, others from the shoulders upwards toward the rump.

Automation of hide removal reduces contamination since there is less handling of the carcass and less use of knives. Moving overhead rails also improve hygiene by reducing carcass contact with operators, equipment such as dressing cradles and with each other since carcasses are evenly spaced.

Small ruminants

Sheep fleeces can carry large volumes of dirt and faeces into the slaughterhouse. It is impossible to avoid contamination of sheep and lamb carcasses when the fleece is heavily soiled. The fleece or hair must never touch the skinned surface, neither must the operator touch the skinned surface with the hand that was in contact with the fleece.

34. The leg is freed from the skin and the hock cut off

35. Pneumatically operated rotating knives (flayers) speed the removal of the hide from the flanks	36. Flaying knives are used for the more intricate parts of hide removal

Combined horizontal/vertical method

The animal is turned on its back and cuts are made from the knuckles down the forelegs. The neck, cheeks and shoulders are skinned. The throat is opened up and the gullet (food-pipe) is tied off (see Fig. 41). The skin on the hind legs is cut from the knuckles down to the tail root. The legs are skinned and the sheep is hoisted by a gambrel inserted into the Achilles tendons. A rip is made down the midline and skinning proceeds over the flanks using special knives or the fists (see Fig. 39). The pelt is then pulled down over the backbone to the head. If the head is for human consumption it must be skinned or it will be contaminated with blood, dirt and hairs.

Moving cratch and rail system. The hanging carcass is lowered on to a horizontal conveyor made up of a series of horizontal steel plates, bowed slightly and divided into sets large enough to cradle a single animal. Two operators usually work together on each lamb performing the legging operations and opening the skin to the stage where it can be pulled off the back. When the gambrel is inserted into the hind legs it is hoisted on to a dressing rail.

Vertical method

At sticking the animal is shackled by one hind-leg and left to bleed. Dressing commences with the free leg which is skinned and the foot removed (Fig. 37). A gambrel is inserted into this leg and hung on a runner on a dressing rail. The second leg is freed from the shackle, skinned and dressed, then hooked on to the other end of the gambrel. The skin is opened down the midline and cleared from the rump.

A spreader frame (a bar U-shaped at each end) spreads the front legs to simplify work on the neck, breast and flanks. The front toes are held in each end of the frame which is then slung up on to a separate travelling hook. The animal is therefore suspended by all four legs belly uppermost (Figs 38 and 39). Skinning continues as in the combined horizontal/vertical method. To clear the shoulders and flanks, the forelegs are freed from the spreader and the feet removed, the animal returning to a vertical position. The skin can now be completely pulled off (Fig. 40), including the head if this is for consumption, though this takes some work with the knife. In both methods, after fleece removal the vent and food-pipe are cleaned and tied off (Fig.41).

37. Fleece removal starts with skinning the free hind leg. Care must be taken to avoid the hide touching the skinned surface or the carcass will be contaminated with faecal matter
38. With forelegs in a spreader frame and hind legs in a gambrel, the sheep is suspended in a horizontal position	40. After skinning the neck and breast, the front legs are freed and skinning continues in the vertical position with the flanks and back
39. The fists can be used to clear the fleece from the breast
	41. After skinning the neck, the food-pipe is freed and tied off to prevent regurgitation of stomach contents