1Dr.Sayyed Mushtaque and 2Dr. Akash Wadal
1General Manager-Breeder and Hatcheries
2Hatchery Coordinator – MH Region
Premium Chick Feeds Pvt Ltd
Chick culling is a common practice in poultry hatcheries, carried out mainly for economic and biological reasons. It involves separating and killing chicks that are considered unprofitable or unsuitable for production—most often male chicks, since they cannot lay eggs and are not efficient for meat production, as well as weak or unhealthy female chicks that would not survive or contribute productively. Because egg-laying breeds and meat-producing breeds are selectively bred for different purposes, raising surplus males would add unnecessary costs, so they are usually culled shortly after hatching or being sexed.
Hatcheries employ trained workers to quickly distinguish between male (cockerels) and female (pullets) chicks, while also checking for signs of illness or defects among the flock. Removing weak or unviable chicks helps maintain overall flock health and reduces the risk of disease. This practice, however, has sparked major ethical and welfare concerns worldwide. In response, researchers are developing alternatives like in-ovo sexing, a technique that determines an embryo’s sex before it hatches, thereby avoiding mass culling. Some countries, under public pressure and with technological advances, have already moved to ban chick culling.
In summary, while chick culling continues as a standard method in hatcheries for efficiency and cost reasons, it remains controversial and is increasingly challenged by demands for more humane solutions.
Welfare Guidelines
The American Veterinary Medical Association (AVMA) requires that euthanasia methods, such as CO₂ gassing, must result in a quick loss of consciousness followed by death with minimal suffering. Only AVMA-approved methods are permitted, including rapid maceration and gas displacement using CO₂ or nitrogen. Procedures must be carried out by trained staff, and hatcheries are obligated to regularly verify that these methods are both effective and compliant with welfare standards.
The National Farm Animal Care Council (NFACC) poultry code specifies that weak, injured chicks or live embryos not intended for further use must be euthanized promptly, and no later than one hour after processing. Hatcheries are required to establish clear standard operating procedures (SOPs) for culling, euthanasia techniques, and proper documentation. Chicks must be handled carefully to minimize stress and injury, and equipment must be routinely inspected to prevent welfare breaches.
Regulations highlight the need for accurate documentation of culling decisions and continuous monitoring of welfare practices. Any mishandling—such as live chicks identified in waste streams—is considered a major compliance violation and requires corrective training or action.
In the European Union and other jurisdictions, laws are standardized to prevent avoidable suffering, mandating the use of approved gases or mechanical euthanasia methods. More recently, governments have begun enacting measures to restrict inhumane practices and shift toward alternatives such as in-ovo sexing.
Rising public concern about animal welfare has intensified opposition to chick culling, with consumers and advocacy groups pushing the industry to adopt non-lethal solutions. Among these, in-ovo sexing—which determines chick sex before hatching—has gained recognition as a promising alternative.
For hatcheries, the central challenge is balancing welfare responsibilities with economic demands and market expectations. To maintain public trust and uphold ethical standards, the industry must focus on transparency, strict adherence to humane protocols, and continued investment in technological innovation.
Mechanism: How CO₂ Induces Unconsciousness and Death
Ø CO₂ euthanasia operates through two main physiological effects: hypoxia (oxygen deprivation) and hypercapnia (excess carbon dioxide in the blood). When animals inhale high concentrations of CO₂, the following occurs:
Ø Carbon dioxide builds up in the bloodstream, causing acidification (lower blood pH), which triggers respiratory distress and rapid loss of consciousness.
Ø Rising CO₂ levels simultaneously reduce oxygen availability, causing hypoxia that further accelerates unconsciousness and ultimately leads to death.
Ø Visible signs such as loss of posture and insensibility occur relatively quickly after exposure, followed by cessation of breathing and, finally, cardiac arrest.
Ø When applied correctly, CO₂ protocols induce unconsciousness before the onset of significant pain or distress.
Ø To minimize suffering, optimal procedures emphasize gradual introduction of CO₂ rather than sudden, high concentrations. Improper gas administration (such as bottom-filling chambers) increases observable distress behaviors, whereas top-fill systems or gradual displacement methods promote uniform distribution and reduce discomfort.
Chamber Design, Equipment, and Safety Protocols
Ø Chamber Design: Hatchery CO₂ chambers are sealed enclosures that allow controlled gas infusion. They range in size to accommodate single or multiple chicks. Gas enters from above to encourage gradual and even filling.
Ø Gas Monitoring: Real-time monitors track CO₂ levels, maintaining effective concentrations (generally 70–90%) to ensure euthanasia is swift but humane. Flow rates must be regulated to prevent distress.
Ø Ventilation Control: Valves regulate gas movement, preventing oxygen from re-entering during euthanasia. After use, exhaust systems release gas safely.
Safety Protocols for Effective and Humane Operation
Ø Regularly inspect chambers for airtight seals to prevent leakage.
Ø Use environmental CO₂ detectors to safeguard workers from accidental exposure.
Ø Ensure staff are fully trained in equipment use, emergency procedures, and welfare guidelines.
Ø Clean and maintain equipment routinely to uphold operational reliability and humane standards.
Standard Operating Procedures for CO₂ Euthanasia in Poultry
Prefill vs. Gradual Fill Approaches
Prefill Method (Immersion)
Ø In this method, the chamber is first filled with a high concentration of CO₂ (close to 100%) before chicks are placed inside.
Ø Birds are immediately exposed to an atmosphere saturated with CO₂, leading to rapid unconsciousness and death.
Ø This approach is generally considered more suitable for poultry, as it minimizes the prolonged distress sometimes observed with gradual filling.
Ø It does not require precise control of gas flow during euthanasia, but chambers must be cleared and cleaned between groups. Since CO₂ is heavier than air, it can accumulate at the bottom, causing uneven exposure if not properly managed.
Gradual Fill Method (Displacement)
Ø Here, CO₂ is introduced into the chamber at a steady rate while birds are already inside.
Ø AVMA guidelines recommend gas displacement rates of 10%–30% of chamber volume per minute, based mainly on rodent studies, to reduce discomfort during induction.
Ø However, for poultry, slower fill rates can cause hyperventilation or distress.
Ø Gradual filling is more commonly used for young swine, while poultry generally respond better to the prefill method.
Concentration and Exposure Guidelines
Ø CO₂ levels of 80%–100% are typically required to achieve humane and effective euthanasia in poultry.
Ø Newly hatched chicks can tolerate high CO₂ concentrations but usually need up to five minutes of exposure to ensure death.
Ø After unconsciousness occurs, gas flow should be maintained for at least 1–5 minutes, or until respiration, heartbeat, and reflexes have completely ceased.
Ø Death must always be manually confirmed; if there is any uncertainty, a secondary method such as cervical dislocation should be used.
Ø Chamber volume, gas concentrations, and flow rates must be accurately calculated to guarantee rapid and uniform displacement of air. Flow rates between 30%–70% of chamber volume per minute are commonly recommended.
Animal Welfare Outcomes
Behavioral Indicators of Distress and Insensibility
· Common behavioral signs observed during CO₂ euthanasia include:
o Headshaking (HS) and gasping (GS): Reflect irritation and breathlessness, signaling distress prior to unconsciousness.
o Loss of posture (LOP): Marks the onset of insensibility.
o Cessation of rhythmic breathing (CRB): Indicates respiratory arrest.
o Cessation of movement (COM): Confirms death.
· Research shows that immediate exposure (immersion) to high concentrations of CO₂ (90– 100%) leads to faster insensibility and death compared to gradual filling methods, while also shortening the duration and frequency of distress behaviors.
· Since distress behaviors appear at lower CO₂ levels than those required for unconsciousness, minimizing the time between exposure and loss of sensibility is critical, particularly for young chicks.
Comparative Effectiveness and Welfare Considerations
· CO₂ euthanasia (immersion method): Considered humane when carried out correctly, ensuring rapid unconsciousness and death.
· Maceration: Provides instantaneous death but is perceived as a more violent physical method, often subject to public criticism.
· Cervical dislocation: Effective if performed properly but requires expertise, with potential welfare issues if done incorrectly.
· Compared with alternatives, CO₂ euthanasia is less physically traumatic and adaptable to large-scale use, though distress during early exposure remains a welfare concern requiring refined protocols.
Practical Application in Hatcheries
Training and Handling Protocols
· Personnel must be trained to:
o Identify signs of distress, unconsciousness, and death.
o Safely operate CO₂ systems and follow emergency procedures.
o Apply correct bird-handling practices to reduce pre-euthanasia stress.
· Backup methods such as cervical dislocation should always be available to ensure death
when needed.
Scalability: Single-Bird vs. Mass Euthanasia
· CO₂ equipment can be adapted for different scales:
o Small chambers: Suitable for individuals or small groups; allow precise monitoring.
o Large chambers: Facilitate batch euthanasia, enhancing efficiency.
· Effective CO₂ distribution is crucial to ensure all animals are exposed consistently.
· Routine maintenance and calibration of equipment are essential for compliance with welfare standards and reliability of outcomes.
Legal, Ethical, and Social Aspects
Compliance with Local and International Regulations
Ø Poultry hatcheries are subject to strict national and international regulations that govern humane euthanasia practices.
Ø In the United States, guidelines from the American Veterinary Medical Association (AVMA) and the National Farm Animal Care Council (NFACC) set standards designed to reduce pain and distress, including protocols for CO₂ euthanasia of chicks.
Ø Within the European Union, unified regulations permit the use of methods such as mechanical grinding and CO₂ gassing. However, several EU member states—such as Germany, France, and Luxembourg—have introduced or are planning bans on chick culling, shifting instead toward alternatives like in-ovo sexing.
Ø Across regions, compliance requires strict adherence to welfare standards, transparent documentation, and accountability within hatchery operations.
Ø Addressing Public Concerns and Ensuring Transparency
Ø Public opposition to chick culling is increasing, mostly due to ethical debates over the mass killing of male and non-viable chicks.
Ø Hatcheries can help address these concerns by openly communicating their euthanasia methods, while also adopting and showcasing alternatives like in-ovo sex determination.
Ø In response to consumer demand and ethical scrutiny, industry leaders are increasingly investing in “no-kill” egg production and other innovative, welfare-friendly approaches.
Future Directions and Ongoing Research
Enhancing Welfare Monitoring
Ø Research is aimed at improving the accuracy of welfare assessment during euthanasia, with a focus on refined behavioral and physiological indicators such as the timing of distress and loss of consciousness.
Ø Emerging sensor-based and automated monitoring systems now allow for continuous, realtime tracking of animal welfare, making it possible to optimize euthanasia protocols more
precisely.
Ø Development of Humane Alternatives
Ø In-ovo sexing technologies enable detection of chick sex before hatching, offering a major alternative that reduces or eliminates male chick culling.
Ø Genetic innovations, including CRISPR-based sex determination methods, are being explored as long-term solutions to prevent the hatching of unwanted male chicks.
Ø Researchers are also testing new gas mixtures and euthanasia technologies to achieve improvements in both animal welfare outcomes and operational practicality. Together, these legal frameworks, societal demands, and scientific innovations reflect a strong and growing commitment to advancing animal welfare in hatcheries—ensuring practices meet both ethical expectations and evolving regulatory standards.