Humane Slaughter of Pigs
All personnel involved in the slaughter of pigs should be trained and have an understanding of the legal requirements for humane slaughter. Injured or sick animals should be killed immediately if not doing so would result in suffering. If appropriate, and under the advice of the Official Veterinary Surgeon, animals may be moved into the casualty pen in which they must receive medical attention and drinking water.
The pigs should be unloaded in a calm manner using a ramp with protective sides to prevent the pigs from falling. Unloading facilities should be designed such that the ramp is never more than 20° and that the surface provides sufficient grip for the animals. Animals should be moved in their transport groups to encourage movement down the race. The lairage must be constructed and maintained so as to prevent any physical injuries to the pigs. It must provide adequate ventilation, light and shelter from adverse weather conditions. The stocking densities should allow all animals to stand or sit at the same time. All animals must have access to clean drinking water at all times. If animals are to be held overnight, they should be provided with suitable bedding unless they are on slatted or mesh floors. Those animals that are likely to become aggressive due to their sex, origin or age must be separated from each other in the lairage.
Animals should be handled calmly and quietly. Only handling aids that encourage movement through sight or sound should be used (eg pig boards or rolled up feed bags). Electric goads must only be used as a last resort and then only for stubborn animals that refuse to move when there is a clear path ahead. It should be applied for no more than two seconds to the hindquarters of an adult animal. The goad should only be used in the race and never in the lairage. Appropriate food must be provided if animals are kept overnight.
The race should have solid sides to direct the pigs forward and exclude distractions. It should be wide enough for two pigs to walk together. Straight races can be used for pigs provided they do not present a dead end. There should never be right-angled bends in a pig race. Lighting that gradually becomes brighter towards the stunning point, without shinning directly into the pigs' eyes, encourages pigs to move forward. Where a restrainer conveyor is used, there must be a system to reduce groups into single files eg a labyrinth system. The conveyor should be tight enough to prevent excessive movement but not so it causes pain or discomfort.
All stunning and killing equipment must be designed to deliver a consistent and effective stun. An appropriately trained person should check all stunning equipment at the beginning of each day. Electrical systems should have voltage and current checked under a load that simulates the impedance of a pig’s head. Captive-bolt equipment must have the velocity of the bolt measured using appropriate equipment and the recuperator sleeves and breech area thoroughly inspected. Gas systems should be checked for leaks from the supply system. There should always be a backup system within reach of the slaughterman. Equipment with moving parts eg captivebolt should be rotated with their backups to prevent disproportionate wear. All equipment should be cleaned and inspected at the end of each working day.
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Stunning methods must be applied in ways that minimise the risk of causing pain distress and fear to the pigs. They should render the animals insensible immediately on application, with the insensibility persisting such that the pig does not recover before it dies from bleeding. Stunning can be reversible therefore it is imperative that animals are bled within 15 seconds of stunning. Pigs may be stunned using electronarcosis or a cartridge powered captive bolt instrument.
To ensure that electrical stunning works effectively, the stunning electrodes should be kept in a good state of repair. The equipment should be tested daily to make sure that it delivers at least 1.3 A at a voltage of at least 260V under a load of similar impedance to a pig’s head. All stunning equipment must have an ammeter and a voltmeter that are easily read by the slaughterman during stunning. The electrodes must be cleaned regularly during stunning (after every 20-25 animals) and must be stored in a cleaning station or on a wall bracket when not in use.
The electrodes should be applied correctly, midway between the eye and the ear, so that they span the brain. Firm pressure should be applied to the electrodes to reduce contact resistance. Since the animals must be bled immediately after the stun, only commence the stunning when there is manpower to carry out the bleeding in a timely manner. The current should be applied for at least 3 seconds. Stunning equipment should have an audible or visual alarm to indicate when the minimum application time has been reached.
The operator should be on the lookout for signs of a good stun. There are two stages indicative of an effective electrical stun, tonic and clonic. Tonic phase signs include:
- Animal collapses and becomes rigid
- No rhythmic breathing
- Head is raised
- Forelegs are extended whilst hind legs are flexed into the body.
Clonic phase signs of a good stun include:
- Gradual relaxation of muscles
- Paddling or involuntary kicking
- Downward movement of eyeballs
- Urination or defaecation
Deviation from the signs above may indicate ineffective stunning. If a stun is suspected to be ineffective, the electrodes must be re-applied and the animal re-stunned immediately. In the event of suspected stunner malfunction, the backup (usually captivebolt) stunner should be used until the electrical stunner is inspected and the appropriate repairs have been carried out.
Carbon dioxide stunning
High levels of carbon dioxide will change the blood’s chemistry and cause disruption in normal brain function. In order for carbon dioxide stunning to be effective, the gas concentration should never fall below 70%. The HSA recommends carbon dioxide levels above 90% to ensure minimum times to loss of consciousness. Gas monitors should be placed at pig level and should give an alarm when carbon dioxideconcentration falls below 90%. If this drops below 70%, all further stunning should be stopped until the equipment is repaired.
Pigs should enter the chamber in groups of at least two. The loading should be smooth with pigs reaching maximum concentration of carbon dioxide in 30 seconds. This prevents the pigs already in the chamber from being exposed to the lower concentrations of carbon dioxide for longer than is necessary. On exiting the chamber, a sample of pigs should be pricked on the nose with a needle. If the pigs move their heads or show any response to the prick, they may be recovering and the whole system should be checked. If the gas does not kill the pigs, they recover very quickly before bleeding can be carried out effectively. They should therefore remain in the chamber for at least 90 seconds to reduce the chances of recovery.
It is generally recommended that electrical stunning or gas killing be used in preference to captive-bolt stunning for adult pigs. When used (usually as backup or for emergency killing), the condition of the captive-bolt device, the cartridge used and the positioning of the device will have a large bearing on the effectiveness of the stun. The correct position of the captive-bolt is 20 mm above eye level on the mid-line of the forehead, aiming towards the tail. The appropriate cartridge size should be used for the size of the animal. Persistent use of underpowered cartridges may cause ineffective stunning whereas overpowered cartridges may result in excessive wear of the equipment. Further details on the correct positioning of the captive bolt and the appropriate cartridges may be found the HSA publications; Guidance Notes 2 Captive-Bolt Stunning of Livestock 3rd Edition (page 12) and Best Practice Guidelines for the Welfare of Pigs in Abattoirs (page 12).
Captive-bolt stunning should only be carried out by a competent and confident technician. After stunning, indicators of a good stun include;
- Animal immediately falls down
- Tongue sticks out of mouth and is limp
- Eyes are fully open
- Pupils are fixed and fully dilated
- There is no blinking reflex of fast eye movements (nystagmus)
- There is no rhythmic breathing
If there is any doubt that the animal has been correctly stunned, it should be re-stunned immediately, preferably with the back-up equipment. All second stuns must be recorded and if they occur regularly, staff may need retraining or the equipment requires servicing.
It is essential that bleeding is done within 15 seconds of stunning so there is insufficient time for recovery to take place before there is irreversible loss of brain function from lack of oxygen. Bleeding is not essential for animal welfare where the pigs are killed by a stun-kill method, but remains important for meat quality. In order to ensure a rapid bleed out, the major vessels must be severed properly. The chest stick method is the best method to ensure a good bleed out. The operator should ensure that the animal is dead by checking for the absence of the brain stem reflexes (blinking when cornea is touched and reflexive gasping breaths). Dressing procedures must not be started until after at least 20 seconds after bleeding has commenced.
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