Meat chickens and layer hens, the main types of poultry farmed in Australia, are two different breeds of birds and are grown for different purposes.
Meat chickens are raised for meat production so have been bred to grow and gain weight very rapidly. Depending on the weight requirements of the market, meat chickens may be ready for slaughter as early as 30-35 days (whole birds) and up to 55-60 days (chicken pieces).
Layer hens are raised for commercial egg production so have been bred to produce a large number of eggs. At around 72 weeks of age hens’ egg production begins to gradually decline and hens are considered ‘spent’ because they are no longer profitable. So that these ‘spent hens’ can be replaced by younger more ‘productive’ hens, they are removed from production and sent for slaughter.
Catching and depopulation
Before poultry are slaughtered, they must first be caught and removed from their housing system, a process known as depopulation. In most cases, poultry are manually caught and placed in transport crates or modules, which are then transported to an abattoir for slaughter and further processing. Unlike meat chickens, due to the low commercial value of spent layer hens and costs associated with transporting birds to an abattoir they may also be killed and disposed of on farm.
What are the animal welfare issues with depopulation?
Depopulation (catching) is stressful because of the significant disturbance it causes to birds from the handling, noise and dust during catching, as well as the disruption to feed and water access prior to catching .
Meat chickens may be subject to partial depopulation, which involves multiple catching events (or ‘pick-ups’) to allow for sufficient space for the remaining birds in the shed. However, this means birds may be exposed to these disturbances multiple times.
Spent layer hens are at high risk of having weakened bones due to calcium deficiency, meaning they may suffer from bruising, injuries and fractures during handling at depopulation. Housing systems, like caged housing systems, where birds are confined and behaviourally restricted, further increases the risk of injuries because layer hens having poor muscle and bone strength due to lack of movement. Moving away from systems where hens are housed in cages brings about benefits to the welfare of hens considered spent. Hens in cage-free systems have better bone and muscle strength and experience fewer fractures at depopulation than hens in battery cages . To read more about the RSPCA’s views on housing layer hens in battery cages click here.
During transport, birds are then exposed to various stressors including weather, the micro-environments of transport modules or crates, minimal space allowance, social disturbance, noise, vehicle vibrations and motion, as well as feed and water deprivation.
At the abattoir, poultry are stunned (rendered unconscious) before slaughter. This occurs either by electrical waterbath stunning (for layer hens and meat chickens) or controlled atmosphere (gas) stunning (for meat chickens). Once unconscious, birds’ throats are cut and bled out to cause death, prior to the birds regaining consciousness.
Where spent hens are killed on farm this is most commonly done using on-farm carbon dioxide gas killing. The meat from spent hens is less desirable for human consumption because layer hens are primarily bred for egg production rather than meat, resulting in differences in taste and texture. When spent hens are slaughtered at an abattoir, they are usually only processed into lower-quality food products such as soups and stocks, or pet food.
Electrical waterbath stunning systems
Electrical stunning is one of the main methods of stunning (rendering birds unconscious before slaughter) used in Australia. It involves birds being shackled upside down by their legs on a moving shackle line. The birds are stunned by passing their heads through an electrified waterbath – the aim being that birds immediately lose consciousness on contact with the electrified water.
What are the animal welfare issues with electrical waterbath stunning systems?
There are significant animal welfare issues with electrical waterbath stunning. How effectively a bird is stunned depends on the correct electrical voltage, current, current type, frequency and application time of the waterbath. If the correct frequency is not applied, or the correct procedures, equipment and settings are not used, it can lead to ineffective stunning or even electro-immobilisation meaning birds are conscious (alive and able to feel pain) during bleed out.
Shackling of conscious birds requires handling and inversion. Hanging birds upside down by their legs causes fear and stress and the compression of their legs by the shackles is painful while birds are still conscious. Severe wing flapping and struggling can also occur while shackled resulting in injuries to wings, and possible painful pre-stun electric shocks. These pre-stun electric shocks can occur when birds’ wings make contact with the electrified waterbath before their heads are immersed. Birds’ heads may also miss the electrified waterbath partially or completely, leading to birds being ineffectively stunned and having their necks cut while conscious.
What are the alternatives?
There are some aspects of electrical waterbath stunning that can be improved in the short term, including system design and settings, gentle handling methods, and catering more effectively to birds of different sizes. However, due to the inherent welfare issues associated with electrical waterbath stunning systems, RSPCA Australia strongly encourages they be phased out and replaced with alternative stunning systems where birds are rendered unconscious prior to being shackled.
Controlled atmosphere stunning (CAS) systems using carbon dioxide, are commonly used as an alternative to electrical waterbath stunning for stunning meat chickens in Australia. In CAS systems, birds are either moved into the stunning module in their transport crates or tipped out and transferred onto a conveyer belt which then moves the birds into the stunner. Birds gradually lose consciousness as a result of exposure to increasing concentrations of carbon dioxide. CAS also has some welfare issues associated with it. High carbon dioxide gas concentrations are aversive to poultry and can lead to hyperventilation, breathlessness, and suffocation. An alternative to carbon dioxide CAS systems and a more humane option, is controlled atmosphere stunning using inert gases. Inert gas mixtures appear to be less aversive, with studies indicating stunning with mixtures of argon or nitrogen gas may be suitable for poultry .
Low Atmospheric Pressure Stunning (LAPS) is a newer method of stunning where birds are placed in a chamber and the atmospheric pressure is gradually reduced, causing birds to lose consciousness gradually due to hypoxia (lack of oxygen). Research suggests that, during LAPS, birds display similar behaviours to that observed during gas stunning, including with non-aversive gas methods such as inert gas mixtures.
Both CAS and LAPS have the benefit of not needing to handle and shackle live birds, reduced stress, and greater uniformity of the stun between birds. However, currently, inert gas CAS systems and LAPS systems are not yet available in Australia for the commercial slaughter of poultry.
 Thaxton Y et al (2016) Symposium: Animal welfare challenges for today and tomorrow. Poultry Science 95(9):2198-2207.
 Toscano M (2018) Skeletal problems in contemporary commercial laying hens. Advances in Poultry Welfare, pp.151-173.
 Berg C, Raj M (2015) A review of different stunning methods for poultry: animal welfare aspects (stunning methods for poultry). Animals 5:1207-1219.