Domestic animals are like human beings in their feelings and anxieties. It is necessary that domestic animals, game animals and birds shall be slaughtered for food as far as practicable- painlessly and without sufferings. Proper bleeding is essential for good quality of meat and this is possible if the animals/birds are made unconscious by different prevailing and approved methods. In Halal method practiced by Muslim and Jewish method, it is assumed that animals are slaughter & by cutting the jugular veins and carotid arteries which immediately produces brain death by drainage of blood. This produces instantaneous insensibility. However, in different method of slaughter and bleeding, it is essential that bleeding of animals should follow immediately after stunning. Thorough bleeding is always necessary for good quality meat.
Animals are stunned to make them unconscious by humane methods before bleeding as per legislation in vogue in many countries. However, there is exception I methods for Muslim and Jewish method of slaughter. However, some countries allow stunning, provided animal is unconscious and not dead. In such case it should be assured that if the animal is not bled, it can regain conscious and walk normally. The higher animals have sensations like human beings with regard to sight and smell of blood, strange noises, movements, surroundings. The animals become panic by their separation from other animals. Therefore, it is to reduce as much stress as possible of animals awaiting slaughter.
The slaughter man for stunning should be trained to use instruments and keep the instrument in proper working conditions. Proper stunning reduces unnecessary suffering of livestock as it will prevents injuries to the animals as well as workers.
In case of hunting of animals, deer, birds, the slaughter and dressing could be done in open area immediately after shooting keeping in mind hygiene. These meats at consumed locally and not allowed for export. The meat of game animals/birds may be tough and dark in colour due to stress and incomplete bleeding.
Stunning
No doubt animal is sacrificed but it should undergo minimum pain during slaughtering. For this purpose, animals are rendered unconscious by different stunning methods. Stunning not only induces immediate state of insensibility but also produces sufficient immobility to facilitate the sticking process to initiate bleeding. As discussed earlier the time gap between stunning and sticking should be minimum. The idea behind the fact is that animal remains unconscious as the sticking induced brain anoxia continues the phase of unconsciousness. The technique utilized in sticking, the species, the age of animal, whether the carcass is suspended or not etc., are the factors which decide the time to reach insensibility because of sticking. For emergency slaughter of animals and animals slaughtered by farmer for his domestic use, the stunning may not be done. However, unnecessary suffering on the part of the animals is avoided.
Signs of effective stunning
The assessment of effectiveness of stunning is topic for research. The signs of effective stunning differs as per method of stunning. However, some typical signs of effective stunning are as follows:
a) Typical signs of effective stunning by mechanical percussive methods:
(i) Immediate collapse of animal
(ii) Muscular spasm
(ii) Cessation of rhythmic breathing
(iv) Protrusion of eye ball.
b) Typical signs of effective stunning by electricity are:
(i) Immediate collapse of animal
(i) Flexion of limbs followed by rigid extension of legs
(iii Arching of back, neck and spine
(iv) Downward rolling of eye ball
(v) Muscular spasm.
(vi) Muscle flaccidity.
c) Typical signs of effective stunning by chemical/carbon dioxide gas are:
(i) Increased respiration followed by dysponea
(ii) Absence of corneal and palpebral reflex
(iii) Muscle flaccidity
Stunning Method
The choice of a particular stunning method depends on many factors like, class of animal, humane aspects, capital and maintenance cost, efficiency equipment, ease of operation, safety of personnel, effect on carcass and brain, religious and legal requirements.
Different methods of stunning are:
- Mechanical stunning
- chemical stunning
- Electrical stunning
Mechanical method
As per the name physical force is used to produce unconsciousness by damaging the brain tissues. It can be further classified under two categories:
(i) Non penetrative mechanical/percussion stunning.
(ii) Penetrative mechanical/prcussion stunning.
Non penetrative method does not make a visible hole to damage the brain tissues. Here a small iron rod is used to strike at head and if practiced with accuracy produces immediate insensibility. Since this method does not involve penetration, brain is edible.
Penetrative mechanical/percussion stunning as per name leads to formation of hole. It produces immediate and permanent insensibility by destruction of brain tissues. The brain can not be utilized for edible purposes because the brain is destroyed by the penetrating bolt. The different ways of penetrative mechanical stunning are:
(i) Captive bolt pistol
(ii) Pneumatic bolt stunner
(iii) Water jet stunning
(iv) Free bullet pistol.
(i) Captive bolt pistol: Generally, Cattle and buffaloes are stunned by captive bolt pistol which is operated by means of a blank cartridge. A bolt attached to pistol is propelled forward on discharge of blank cartridge and automatically recoils into the barrel. The cartridge of correct strength should be used. For small animal cartridge of one grain (1 grain = 0.065 grams) strength and for large animal cartridge of three to four grains are used. Captive bolt pistol produces immediate insensibility by destruction of the cortex and deeper part of the brain and changing the intracranial pressure by producing sudden jerk. Captive bolt pistol is effective in cattle, buffalo, sheep and calves but not effective in bulls, pigs in which frontal bone is very thick. This type of stunning can not be practiced for a faster (> 250 animals 1 hours) rate of slaughter. Blood splashing i.e., muscle haemorrhages occur in this method if the time between stunning and sticking is prolonged.
(ii) Pneumatic bolt stunners: Here bolt is activated under high pressure (80 to 120 psi) to achieve high velocity.
(iii) Water jet stunning: The method was devised by Lamooij. Fine jet of water is utilized to penetrate the skull. Usually jet of 0.5 mm at pressure of 3500 to 4000 bar is applied.
(iv) Free bullet Pistol: These were in use in older days and even being practiced to euthenize horses at some military farm. Great care and expertise is required while using this method to avoid accidents. In case of BSE suspected animals or other brain diseases this method should not be used.
In case of cattle some where it is in practice to destroy motor centers of the brain by insertion of a long thin rod or closely coiled wire into the hole made by penetrating bolt of the pistol. This helps in avoiding injury to operative and speeding the carcass dressing by preventing the chances of reflex muscular action at the time of sticking. The process is called "pithing". The length of rod should be appropriate otherwise it may damage nerve to spleen (splanchnic nerve) leading to a condition 'slaughter spleen' where spleen is congested and enlarged.
The site of application of penetrating mechanical stunner is very much important. The instruments should be firmly held against the animal's head at proper point and direction. The point of application for different animals is as follows:
Adult Cattle/Buffalo: The cross point at middle of forehead where two lines taken from medial canthus of each eye to base of opposite horn or horn prominence's cross.
Calves: Slightly lower than the cross point at middle of forehead as in adult.
Bulls and old cow: Same as adult cattle but 1.5 cm to the side of frontal ridge.
Horse: One cm above the crossing points of lines connecting inner canthus of eye to ear base of opposite side.
Hornless sheep and goat: At the top of the head and direction is towards the gullet
Horned sheep and goat: At the top of the head behind the ridge connecting two horns and direction is towards the gullet.
Pig: In the center of forehead 2.5 cm above the eye level and direction towards cranial cavity.
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| Points of application for mechanical stunning for different animals. |
Chemical method
It is well known that the chemicals can be used as an anesthetic agent before operation. Various gases and their combination are also being used to make the animal unconscious. Gases such as N2O (nitrous oxide), CO2, argon, oxygen mixture are being used to stun the animals. The main aim is to induce anoxia so that animal becomes unconscious. The induction time and the respiratory distress are two important factors in selecting the gas and its concentration. N2O has a higher induction time while CO2 being irritant produces respiratory distress at higher concentration. Similarly a mixture of two per cent oxygen and argon induces unconsciousness but it is slow process to be used commercially.
Carbon dioxide anesthesia is an effective stunning method. It is suitable for pigs. Carbon dioxide is stored in cylinders or bulk tanks or liquid under pressure. It is also available in solid form as dry ice for refrigeration purpose. The gas blocks the nerve endings and reduces the speed of nerve impulses.
A concentration of 65 to 70 per cent CO2 in air is most suitable for pre slaughter anesthesia. The exposure period is 45 seconds and bleeding should take place within 30 seconds of the pig leaving the gas chamber. One disadvantage of using a carbon dioxide chamber is that pigs differ some what in their susceptibility to anesthesia by gas, and that individual control of the animals is not feasible. Therefore, animals are exposed for different time to chamber with different concentration of CO2 or a concentration of around 65 to 70 per cent CO2 is used. If the concentration is too low, animals will not be stunned properly and if too high, the animals will become stiff and bleed poorly. Superficial congestion occurs when the exposure period is too long. Since animals start recovering in an average of 90 seconds, therefore, sticking should be performed immediately. Similar types of concentration are used for sheep but operation is more expensive as the Inspection presence of fleece requires more gas. The CO2 anesthesia also can be utilized for turkeys (73-77% CO2) and chicken (70%).
The CO2 anesthesia is advantageous because-
- Meat and offal are free from harmful residues,
- Relaxed carcass allows easier dehairing and dressing,
- Less noise,
- Reduced labor requirements, muscular haemorrhages can be avoided due to stimulated bleeding and
- Lower pH of the meat due to application of CO2.
CO2 anesthesia is found to be associated with better bleeding as CO2 stimulates respiration favoring blood circulation. There are three main forms of apparatus used for CO2 anesthesia depending upon the rate of slaughter-
(i) Oval tunnel: A slot conveyor carries the pigs through an oval tunnel which slopes downwards at an angle of 30 degres to the anesthetizing chamber. This is used for higher killing rate, e.g., 120- 140 pigs/hour.
(ii) Dip lift: When animals enter the cage, it descends vertically to the CO2 pit where they remain for the pre-set time and then automatically return to the ground level. It is suitable for smaller throughput's.
(iii) Ferris wheel: This is a horizontally revolving apparatus divided into three compartments operating in such a way that when one section is uppermost the other two are submerged in the gas chamber.
Electrical method
In this method, an alternating current is passed through the brain/heart of the animal. Electrical stunning is being used from the year 1930; however, there is some problem of missed shock, animal is paralyzed but still conscious. Electrical stunning causes cerebral nerve cells in coordination resulting in unconscious state of the brain. In electrical stunning, the current must be carefully controlled, otherwise complete unconscious state may not be attained and there may be convulsive muscular contractions. Electrical stunner is now provided with indicator of voltage fluctuation, time indicator to the guide of proper stunning etc.
The electrodes of stunners are kept moist for proper shock while head of the animals are kept clean and dry. High voltage may result into death of animal. Splashing of water over the head of animal is not desirable as it may cause short circuit. Sometimes hemorrhages are observed in muscle tissue and lungs due to electric stunning, this can be avoided by proper resting of animals prior to slaughter and proper stunning followed by immediate bleeding. For production of genuine anesthesia by electrical method, following factors to be considered-
The strength of the electric shock should be of sufficient magnitude. The strength of the current should not be less than 250 mA and the voltage should not be less than 75 V.
The current should be applied for a sufficient time to induce an electroleptic shock. 10 seconds is recommended for a genuine shock.
The electrodes should be correctly positioned so that current will pass through the thalamus and cortex of the brain.
The animal should be immediately bled after unconsciousness has been produced.
As per operational voltage. electrical stunning can be studied under following headings:
a) Low voltage electrical stunning: An electrical current of low voltage i.e., 70 to 80 volt is manually passed through the brain of an animal for about 7 to 10 seconds to produce unconsciousness. A pair of head tong is suitable for pig and sheep. The electrode is applied with pressure. Automatic electric stunner for pig and poultry are suitable.
b) High voltage electrical stunning: Effectiveness of low voltage stunning has caused some doubts regarding proper stunning of animals. Therefore, high voltage stunners using 300V are now available but have to be used with caution both for animals and the operator. Brain function stops within 2 to 3 seconds after high voltage stunning and the animal is killed before bleeding. Therefore, this method of slaughter of dead sheep or goat or cattle would not be accepted in ritual methods of Muslim and Jews. Automatic high voltage stunners are now available for proper stunning of animals for pig and sheep.
Poultry stunning: Different types of electrical stunners are used in poultry depending upon the speed of operation in commercial poultry dressing plant. Hand stunning is also practiced in smaller units using transformer to provide 50 to 90 V. This is suitable for chicken around two kg. body weight using 70 V for one-three seconds and for turkeys of 6.0 to 9 kg. body weight at 90 V for 10 seconds. In high-speed poultry dressing line, 400-1000 V is carried in a grid over which the shackled birds are conveyed. Usually the grid touches the comb but may also involve other parts of bird. The disadvantage is cardiac arrest due to high voltage electrical shock. 50 to 60 V AC current causes sufficient narcosis without any cardiac shock and thus is preferable to high voltage (400-1000 V). An automatic poultry stunner using 70 V for chicken in which head is drawn through electrified water bath is found suitable.
Bleeding
Stunned animals must be positioned first for bleeding. A vertical or hanging position is achieved by shackling below the hock of one hind leg and hoisting the animal (head down) to a convenient height. The actual bleeding operation is made by sticking or inserting the sticking knife through the neck behind jaw bone and below the first neck bone. Purpose of this is to severe the blood vessels and let out blood. Bleeding should be as complete as possible. Insufficient bleeding and slow death indicates incomplete severance of the blood vessels. Practice and experience are needed for successful bleeding operation. Keeping quality of carcass depends on the efficiency of bleeding. The stunning results in increased heart rate and rise in blood pressure which facilitate immediate bleeding. The rate of blood flow from cut vessels is 5-10 times more rapid than in the intact vessel and an undue interval between stunning and bleeding may lead to imperfect bleeding and blood splashing.
Bleeding of cattle/buffalo: Two main methods i.e., unilateral and bilateral bleeding are followed in cattle/buffalo. Carotid arteries and jugular veins of both side of the neck are incised across the throat region in case of bilateral bleeding. Knife is directed towards the entrance to the chest to cut the brachiocephalic trunk and anterior venacava through an incision in the jugular furrow at the base of the neck in case of unilateral bleeding. Knife should not pass too far towards the chest to avoid puncture of pleura and aspiration of blood into thoracic cavity,
Bleeding should be continued for 6 minutes and the average amount of blood obtained in cattle slaughter is 13-14 kg. In calves, slow bleeding is desirable to ensure white color of veal.
Bleeding of sheep/goat: Usually both carotid arteries and jugular veins are incised in the jugular from close to the head. In some cases the trachea, esophagus and spinal cord are also severed at the atlanto-occipital junction. Bilateral technique is the easiest to perform and produces satisfactory bleeding. The bleeding time for sheep/goat carcass is 2-5 minutes. 1-2.5 kg. blood is available from a slaughtered sheep/goat. Generally, sheep/goat bled in the horizontal position loses more blood than those suspended vertically.
Bleeding of pig: The knife is inserted in the mid line of the neck at the depression in front of the sternum and then pushed forward to severe the anterior vena cava at the entrance of the chest. Knife should not be inserted too far because it may penetrate into the shoulder and allow blood as well as scalding water to run back into the shoulder pocket to give a cooked appearance. Sometimes, urination occurs while the pig is bled and that renders the blood unmarketable. Pigs should be allowed to bleed for 6 minutes and the average blood yield from pig ranges from 2.2 kg. to 3.6 kg. depending upon the size of the pig. In some abattoir, pigs are bled by prone sticking where the pigs are stuck while lying prone. This is more advantageous because of more efficient recovery of blood.
