During handling and moving towards the stunning area, pigs shall be handled according to their biology and to avoid pain and distress. This is because the latter results in pigs hesitating and halting, causing piling up, turning back, slipping or falling, and a suboptimal slaughter process. For each stage of the slaughter process, i.e. unloading from the vehicle, lairage, moving to the stunning area, stunning, possible hoisting, and debleeding, a specified SOP must be in place and applied. This is to be monitored by the Animal Welfare Officer.
In EURCAW-Pigs’ “Review of pig welfare in slaughterhouses at stunning and bleeding”, suggestions for improved practices are provided to minimise welfare problems for each of key areas relevant for pig welfare immediately related to stunning and killing:
Handling prior to stunning
During handling and moving towards the stunning area, pigs shall be handled according to their biology and to avoid pain and distress:
- A factor that is extremely stressful is isolation for individual (manual) electrical stunning, or into a single file for automated electric stunning, especially with a high slaughter speed. For CO2 stunning, pigs are driven in small groups into the stunner, which is less stressful.
- The use of excessive pressure can be reduced using simple improvement measures, e.g., management of light and airflow encourages pigs to move into single files before stunning. Disturbing noises should be avoided, e.g. metal gates banging on metal (using rubber protection), noises from hydraulic slaughter apparatus and vocalisations of conspecifics, etc.
Stunning, i.e. electrical and CO2 stunning
Electrical stunning involves passing an electric current through the brain of the pig to induce a generalised epilepsy and immediate loss of consciousness. Effective electrical stunning results, e.g., in:
- Immediate loss of consciousness, collapse of the hind and tonic rigidity followed by tonic-clonic seizures.
- Immediate loss of breathing and presence of breathing indicates an ineffective stun.
- Recovery may start after 30 sec and de-bleeding takes 20-60 sec to result in cerebral hypoxia, so sticking should be done as fast as possible following stunning, i.e. during or towards the end of the tonic phase or at the very start of clonic activity, and preferably before hoisting of the body.
In Controlled Atmosphere Stunning (CAS) using CO2 small groups of pigs are exposed to a high concentration of CO2 leading to depression of brain activity and loss of consciousness:
- CO2 (above 40%) is pungent and painful to inhale and leads to highly aversive responses indicative of fear, pain and respiratory distress (‘air hunger’). It takes approximately 15-20 sec before pigs lose consciousness (depending on the CO2 concentration).
- Stunning effectiveness depends on e.g. the CO2 concentration, duration of exposure, maximum stun-to-stick interval and the quality and temperature of the gas.
- Devices must be in place displaying and recording the gas concentration and exposure time, and giving an alarm in case of insufficient gas concentration (< 80% CO2).
Bleeding must be performed soon after stunning to avoid animals regaining consciousness before they die as a result of blood loss:
- Slaughter pigs are usually killed by bleeding using a chest stick severing the common brachiocephalic trunk.
- Before sticking, unconsciousness of the animals must be ascertained. Animals being conscious at sticking or regaining consciousness during bleeding are likely to have poor welfare, as the incision is painful.
In the next section on welfare indicators, examples of relevant clinical conditions and signs of physiological weaknesses will be listed (forthcoming).
Source photo: ©EURCAW-Pigs