By Richard Blatchford, PhD, University of California, Davis
The egg industry in the United States maintains approximately 300 million hens each year (United Egg Producers, 2025). For every laying hen that is hatched, approximately one male counterpart also hatches. However, as roosters do not produce eggs, they are typically culled, or euthanized, at hatch. However, the culling of these day-old male chicks raises ethical concerns. In an attempt to find an alternative to culling, new technologies such as in ovo sexing (determining the sex of the chick during embryonic development) are being researched.
Sexing chicks
Sexing is the process of determining whether a day-old chick is male or female. There are several techniques that can be employed to sex chicks. Manually sexing chicks involves looking at the vent for slight differences in anatomy that correspond with being male or female. Professional sexing is a highly skilled art, and can achieve a success rate of98% or higher. Genetic advancements have allowed for easier visual sexing techniques. These involve color and feather sexing (see box) and are also highly accurate.
Culling techniques
Once a chick is determined to be male at the hatchery, it is then culled following an American Veterinary Medical Association (2020) approved method.
Maceration
This technique involves instantaneous mechanical destruction of the chick. Death by this method is instantaneous, and therefore considered humane.
Gassing
Death by gassing takes slightly longer than maceration and is typically achieved using carbon dioxide. Several chicks are placed into a chamber and are exposed to levels of carbon dioxide that act first as an anesthetic, then higher levels of gas are administered to result in death. The two-step process is important for ensuring a humane death.
Alternative to day-old culling
While maceration is the predominate method of euthanasia in the United States, gassing also raises ethical concerns. Some European countries have banned male layer-type chick culling. But what are the alternatives? One promising technique is in ovo sexing.
In ovo sexing
This technique involves identifying the sex of an embryo in very early stages of development. This technology is advancing in response to the ethical concerns surrounding the culling of day-old chicks. Many types of technology have been developed.
There are two main categories of in ovo sexing techniques. The first are called non-optical methods. These typically include invasive technologies that need to open the shell of the egg to extract samples for further processing. The second category is called optical methods. These are generally non-invasive, although some require a small hole in the eggshell (see Corian et al., 2023for detailed explanations of these technologies).
Examples of the two main types of in ovo sexing technologies.
Optical |
Non-optical |
|
Nuclear magnetic resonance spectroscopy |
Genetic engineering |
|
Infrared spectroscopy |
DNA analysis |
|
Visible near infrared spectroscopy |
Immunosensing |
|
Morphometric studies |
Volatile organic compounds |
Although many ways of performing in ovo sexing have been developed, few have been adopted for practical use. In order to be effective on a commercial scale, the technology must conform to 6 characteristics, including:
- Be able to sex embryos in both white and brown eggs
- Be as accurate as a human sexer (98.5% or higher)
- Be used before the embryo is capable of feeling pain, which may be as early as 9days, though more likely at day 12, based on brain wave studies (Kollmansperger, 2023)
- Not interfering with embryonic development or hatchability be capable of processing high numbers of eggs/hour
- Have little economic impact on production costs
Is in ovo sexing available in the United States?
No technology has been able to meet all 6 of the criteria for commercial adoption. However, some of the in ovo sexing techniques have been adopted in other countries where chick culling has been banned. The egg industry in the United States has agreed to adopt in ovo sexing when a technology becomes commercially available. One of these technologies will now be employed in the United States in2025.
The technology uses a laser to drill a small hole in the eggshell and takes a drop of allantoic fluid, which contains DNA and can be sampled away from the embryo. This occurs at 9 days of incubation, is considered non-invasive, and does not disrupt embryonic development. The hole created is sealed with beeswax.
This will be the first commercial use of this technology in the United States, and shows promise as an alternative to culling day old chicks. As research continues to refine the in ovo sexing technologies, others may be adopted as well. In ovo sexing is a promising alternative to culling day-old chicks. Embryos are sexed and culled before the onset of pain sensation, making these technologies welfare friendly, and may alleviate the ethical concerns related to the culling of day-old male chicks.
Further Resources
American Veterinary Medical Association. 2020. Guidelines for the euthanasia of animals. https://www.avma.org/sites/default/files/2020-02/Guidelines-on-Euthanasia-2020.pdf
Corion, M., Santos, S., De Ketelaere, B. et al. 2023. Trends in in ovo sexing technologies: insights and interpretation from papers and patents. J Animal Sci Biotechnol 14:102. https:// doi.org/10.1186/s40104-023-00898-1
Kollmansperger, S., Anders, M., Werner, et al. 2023. Nociception in chicken embryos, Part II: embryonal development of electroencephalic neuronal activity in ovo as a prerequisite for nociception. Animals, 13:2839. https://doi.org/10.3390/ani13182839
United Egg Producers. https://unitedegg.com/facts-stats/. Accessed 2/25/2025
https://layinghens.hendrix-genetics.com/en/technical-support/hatching/
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