Stunning before slaughter

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Stunning before slaughter

Stunning before slaughter

According to EU regulation 1099/2009, all animals slaughtered in Denmark/EU must be sufficiently stunned before slaughter. The purpose of the stunning procedure is to induce insensibility to pain until the animal is dead, and the procedure must therefore ensure that no animals regain consciousness before, during or after sticking. However, suboptimal stunning can induce pain, and the handling prior to stunning can also involve fear and pain. Therefore, optimal handling prior to stunning combined with the correct stunning procedure is crucial to the welfare of the animals during this stage of the day of slaughter.


All medium-sized and large pig abattoirs in Denmark use CO2 for stunning before killing. The CO2 backloader is by far the most animal-friendly system for handling and stunning pigs, when adjusted and used correctly.

The handling of the pigs in the race takes the natural behaviour of slaughter pigs into consideration, and, when the layout of the plant is designed correctly and the push-hoist gates are correctly synchronised, the pigs usually move forward automatically, with no need to be pushed by the moving push-hoist gates.

The quality and duration of correctly performed CO2 stunning and the correct handling of pigs are close to ideal, resulting in almost no understunning, something which no other stunning method suited for abattoirs can achieve.

However, no method is completely free of problems, and gas stunning takes some time to be induced (10-25 seconds from the introduction of the gas). At DMRI, we strive to improve and optimise routines to alleviate and minimise aversive reactions.

After loss of consciousness, some pigs get cramps (excitation). The cramps during the excitation phase can be absent, mild or sometimes severe. However, it is important to stress that they are of no significance to animal welfare, because the animals are unconscious. However, it is important to try and prevent severe excitation in order to prevent blood splashes and other quality problems caused by severe excitation. Excitation can be improved or reduced by optimising the pre-stunning handling.


Electrical stunning

Head-to-body electrical stunning is used to stun approximately 80% of industrially slaughtered broiler chickens worldwide. The most common method is the submersion of the head and neck of the shackled bird into an electrical water bath for a minimum of 4 seconds. EU regulation 1099/2009 allows certain combinations of average frequency and amperage per bird. However, water bath stunning has some drawbacks concerning animal welfare. The birds are shackled when conscious, and the same voltage, and therefore a different amperage, is applied for birds of different size. This increases the likelihood of some birds being understunned and other birds being subjected to more amperage than necessary, which increases the risk of quality defects such as broken bones, muscle blood splashes and red wing tips. Optimal stunning is necessary for the correct positioning of head and neck to ensure optimal neck cutting in the automatic killing machine. High-speed cameras can be used to show the procedure in detail and to identify where birds are at risk of not being stunned and killed in the best possible way.

There is a need to invent a more animal-friendly method for electrical stunning of birds, due to the demand from large numbers of customers across the market for reversible stunning. At present, the only alternative to water bath stunning is CO2 stunning, which is only economically feasible for large abattoirs.

CO2 stunning

CO2 stunning of poultry has several animal welfare benefits over electrical stunning. There is no shackling or other type of handling of conscious birds, and in some systems the birds even can remain in their crates until they are unconscious. This is a major improvement in animal welfare compared with electrical stunning. The quality and duration of the stunning is also generally outstanding in well-adjusted facilities.

The method requires an exact knowledge of the average weight per bird and the number of birds per crate in order for the stunner to be adjusted correctly with regard to gas concentration, exposure time, and output speed. Due to the high speed of poultry slaughter lines, it is important to synchronise the output of the stunner and the speed of the production line and ensure that post-stunning shackling is efficient in order to minimise time between stunning and killing.

No method is completely free of problems, and gas stunning takes some time to be induced. CO2 stunning of poultry is a more gradual process than CO2 stunning of pigs. The process consists of two phases, the first phase requiring a low CO2 concentration, thereby minimising the aversive responses. However, gasping and probably also neck stretching are natural responses to an increased level of CO2 in the blood stream, and this occurs in birds even at levels as low as 2-4 % CO2. It is not a sign of suffocation, but rather a manifestation of the exact same mechanism that occurs when you run up and down the stairs several times: your body increases O2 consumption and produces more CO2, leading to an increased heart rate and faster and deeper respiration, so that the increased level of CO2 is exhaled and more O2 can be inhaled. This is what happens in animals that are stunned with CO2. During the time from exposure to loss of consciousness, aversive response can be seen in a varying number of the birds.

After loss of consciousness, the birds are introduced to the second phase – a higher CO2 concentration. However, stressed birds and inadequately adjusted stunning programmes can cause excitation (convulsions) after loss of consciousness. This can easily be observed from birds lying on their backs and sometimes also from injuries on the top of their heads. These problems can be corrected through adjustment of the stunning programmes, accurate weight estimate of the birds and optimal handling of birds during transportation and in the lairage. Although this phenomenon is not an animal welfare issue, a high level of excitation can indicate stress before stunning and can be relatively costly due to injuries and downgrading of the carcass.

Also for CO2 stunning of poultry, it is essential that the production line is correctly designed right from the start. It is certainly possible to optimise existing facilities, often resulting in a significant improvement in the working environment and a decrease in quality defects.