The development of the poultry industry has led to birds being genetically selected for different purposes – either egg or meat production. Laying hens are bred to produce as many eggs as possible with a minimal amount of weight gain. Only females are used in the laying industry, but it is not economically viable to keep the males of laying strains for meat production. As a result, millions of day-old chicks are killed each year in hatcheries because they are males and thus not needed for egg production. In addition, in layer and broiler hatcheries, there are chicks that are killed upon hatching if they are sickly or deformed in order to prevent their welfare from being further compromised.
Whenever an animal is intentionally killed by a human, it must be done using a humane method, causing no pain and with the least amount of stress experienced by the animal. In the UK, operators involved in the killing of chicks have a legal obligation to ensure they do not cause any “avoidable pain, distress or suffering” under the Welfare of Animals at the Time of Killing Regulations 2015 (WATOK) (Legislation.gov.uk, 2012, 2014a, 2014b, 2015). Similar obligations are listed in the EU regulation on the protection of animals at the time of killing (Legislation.gov.uk, 2009).
Whenever an animal is intentionally killed by a human, it must be done using a humane method, causing no pain and with the least amount of stress experienced by the animal
When day-old chicks are killed in hatcheries, a humane method must be used to comply with UK and EU legislation. Humane killing can be achieved using a mechanical apparatus that causes immediate death or by exposure to specified gas mixtures. A third method, killing by cervical (neck) dislocation, must not be used routinely and is recommended by the HSA for use only in emergencies.
Instantaneous mechanical destruction
Although aesthetically unpleasant, instantaneous mechanical destruction (IMD) is a humane and effective killing method for day-old chicks when the equipment is used, managed and maintained correctly. Different designs of IMD equipment exist but always consist of rapidly rotating and interlocking projections or blades, leaving a very narrow gap. When day-old chicks enter the IMD equipment, either manually by a trained operator or from a conveyor in a single layer, they are instantaneously fragmented, resulting in immediate death. When functioning correctly, the IMD process is so quick that no pain is inflicted.
For a mechanical apparatus to be considered humane and comply with legislation, it must cause immediate death to each chick. This requires the IMD equipment to be installed and calibrated following the manufacturer’s specifications and regularly inspected, cleaned and maintained. When used in a commercial hatchery, the equipment must have a capacity that can cope with the high throughput, which is a prerequisite for the IMD equipment to work efficiently.
For a mechanical apparatus to be considered humane and comply with legislation, it must cause immediate death to each chick
Recent videos circulating on social media show IMD equipment that is not working as described above, which leads to preventable suffering for the chicks and is illegal. Such incorrect usage needs to be stopped and prevented. These videos do not illustrate how efficient and humane the method is when the equipment is used and maintained properly by trained staff.
The principle of gas killing is to deprive the brain of oxygen. This is achieved through inhalation of a gas mixture with a very low oxygen content. Neonates, such as day-old chicks, are very resistant to oxygen deprivation. It is therefore necessary to expose chicks to gas mixtures with very little residual oxygen for a considerable amount of time to ensure they are dead and not just unconscious (stunned). For this to be humane, chicks must be placed into the gas mixture and remain there until they are dead. As the killing of chicks with gas mixtures does not result in an immediate loss of consciousness, it is important to ensure the induction of unconsciousness does not cause distress.
In addition, the type of gas used must be suitable for a commercial environment. A humane and efficient gas mixture must be non-aversive, induce loss of consciousness as rapidly as possible and be capable of killing chicks. It should be safe for use in commercial conditions, easy to contain within an open container and, ideally, relatively cheap.
What gas mixtures should be used for the humane killing of day-old chicks?
The gases most commonly used to replace oxygen in a gas mixture are carbon dioxide (CO2), argon (Ar) and nitrogen (N):
- Carbon dioxide is relatively cheap, heavier than air (therefore easy to contain) and produces rapid unconsciousness when inhaled at high concentrations. However, carbon dioxide is an acidic gas, and scientific research has shown it can cause head shaking and gasping in chicks at concentrations over 25 percent, indicating it is unpleasant to inhale
- Argon is also heavier than air and more expensive than carbon dioxide, but it is non-aversive
- Nitrogen has the same properties as argon apart from being slightly lighter than atmospheric air and thus more difficult to contain in high concentrations
When exposed to gases or gas mixtures, the time taken for chicks to lose posture is an indication they are approaching loss of consciousness. This does not differ much when chicks are exposed to any of these gases, but the behaviour of chicks before loss of consciousness indicates that the inert gases do not cause any apparent respiratory discomfort. A humane gas mixture for killing day-old chicks would therefore contain either argon or nitrogen and less than 25 percent carbon dioxide. Although legal in the UK, the HSA does not consider inhaling 100 percent carbon dioxide an acceptable method for killing day-old chicks.
As young chicks are very resistant to oxygen deprivation, a maximum of 2 percent oxygen should be included in the gas mixture
As young chicks are very resistant to oxygen deprivation, a maximum of 2 percent oxygen should be included in the gas mixture. According to UK legislation, a gas mixture for use in hatcheries can be 90 percent argon (or other inert gas) mixed with 10 percent air. The latter results in approximately 2 percent oxygen being included, as air contains 21 percent oxygen. This is the least aversive of the legal gas mixtures for killing day-old chicks. The HSA recommends at least 95 percent argon mixed with 5 percent air (which brings the oxygen concentration below 1 percent).
It should also be noted that convulsions may occur with all these gas mixtures, but these start only after loss of consciousness and therefore do not have any welfare implications.
In some EU countries, the routine killing of day-old male chicks in hatcheries has been outlawed, and there are movements in place to make this ban applicable in all EU member states. It is arguably an ethical problem that the production of eggs for human consumption currently involves breeding birds that are killed soon after hatching. However, it is not an animal welfare issue provided day-old chicks are killed humanely.
As outlined in this article, it is possible to achieve the humane killing of day-old chicks by employing well-functioning and properly maintained mechanical destruction equipment or by exposure to gas mixtures that are non-aversive to the chicks, that lead to rapid loss of consciousness and that contain a sufficiently low oxygen content to ensure the death of birds.
Even without the routine killing of male chicks, all hatcheries need to have methods in place for the humane killing of sick and deformed birds.