In-ovo Sexing / Hatching Eggs

In-ovo Sexing / Hatching Eggs

In-ovo sexing

1. The Problem

Commercial layer hatcheries produce two kinds of chicks from every fertilized egg: females, which grow into laying hens, and males, which cannot lay eggs and belong to a breed line not suited for meat production. Historically, both sexes were hatched and then sorted, and the male chicks were culled on their first day of life. This practice happens at massive scale (billions of male layer chicks culled per year worldwide)1-3 and has become a major animal welfare concern.

In the Netherlands, the government has set an end of 2026 deadline4-6 to stop this practice. The solution the industry is converging on is not to change what happens after hatching, but to determine the embryo’s sex while it is still inside the egg, early enough in incubation that the embryo is not considered capable of pain perception10,11, and then stop incubating (or redirect) the male eggs before that point.

The methods currently used commercially work, but each comes with a real cost or throughput problem:7

  • Hormonal / biomarker fluid tests: accurate, but they require a small hole drilled into the shell to extract fluid, are relatively slow per egg, and involve consumable reagents and lab style processing, all of which add up in cost per egg at hatchery scale.
  • MRI plus AI: accurate and non-invasive, but the equipment itself is very expensive to buy and maintain, and throughput is limited, making it hard to scale to the volumes a commercial hatchery processes daily.
  • Imaging Spectroscopy: workable, but the cameras and computation needed are costly, and processing full images per egg is slower than a simpler point measurement.

This leaves an opening for a method that is non-invasive (no hole in the shell), fast enough for high-throughput commercial lines, and cheaper to deploy than MRI or hyperspectral systems, which is exactly the gap that lower-cost spectroscopic approaches are aimed at.

2. Production Chain

  • 1. Parent stock breeding: pure line and grandparent stock farms maintain the genetic lines used to produce commercial layer hybrids (e.g. Hy-Line, H&N, Isa Brown)8,9.
  • 2. Hatching egg production: parent stock hens lay fertilized hatching eggs, which are collected, graded and stored under controlled conditions at dedicated hatching egg farms.
  • 3. Delivery to the hatchery: fertilized eggs are transported to a commercial hatchery (in the Netherlands, mainly Pluriton, Ter Heerdt-Verbeek Productie, and Agromix Broederij).
  • 4. Incubation start (day 0): eggs are set in large incubators under controlled temperature and humidity.
  • 5. Sex determination window (day 8 to 14): this is the stage where in-ovo sexing takes place, ideally completed before day 13.
  • 6. Divergent path after sexing: female eggs continue incubation normally; male eggs are removed from incubation before the pain-perception threshold, rather than being hatched and culled afterward.
  • 7. Hatch (around day 21): female chicks hatch.
  • 8. Post-hatch handling: chicks are vaccinated, sorted and boxed for transport.
  • 9. Rearing farm (pullet rearing): young hens are raised to laying age (roughly 16 to 18 weeks).
  • 10. Laying farm: hens produce table eggs for the remainder of their productive life.
  • 11. Egg collection and packing station: table eggs are graded, stamped, and packed (this is a separate part of the chain from the hatching egg producers, since packing stations handle unfertilized table eggs for consumption).
  • 12. Distribution and retail: packed eggs move through distributors to supermarkets, food service, and other retail channels.

3. Where NIR Can Determine Egg Sex, Before the Chicks Are Culled

The specific point in the chain where NIR contributes is step 5 above, the incubation window between roughly day 8 and day 14, before the eggs hatch and before any chick is culled.

For brown-shell breeds (such as Isa Brown, which show a gender-specific down feather color, brown in females and yellow in males), the developing embryo’s pigmentation becomes spectrally distinguishable well before it becomes visible to the eye. Visible-near-infrared (vis-NIR) point spectroscopy, shining light through the shell and reading the reflected or transmitted spectrum, can detect this pigmentation difference non-invasively, without drilling any hole in the shell.

Peer-reviewed research on this method has demonstrated:12-14

Day 12~86%12too early
Day 13≈98%12already accurate
Day 14>99%12,13best accuracy
  • A narrow slice of the spectrum (roughly 749 to 861 nm) is already enough to classify most eggs correctly, meaning smaller, simpler, and cheaper spectrometers can be used instead of a full hyperspectral camera12.
  • Measurement is done on a single point of the egg rather than a full image, which makes each individual reading fast, an important factor for high-throughput commercial lines12.

This combination (accuracy above 97 to 99 percent from day 13 onward, no invasive hole, and a simpler, cheaper sensor than hyperspectral or MRI) is what positions vis-NIR as a lower-cost complement or alternative to the currently used hormonal, biomarker, and MRI-based methods, while still meeting the pre-day-13 welfare requirement.

4. Other Moments in the Egg Production Chain Where NIR Contributes

In-ovo sexing is only one use of NIR in this chain. Later on, at the table egg side of the business (step 11 onward, packing stations and retail rather than the hatchery), NIR is separately useful for freshness and age related quality control:

  • Freshness estimation without breaking the egg: freshness is traditionally measured with the Haugh unit (HU), which requires cracking the egg open to measure albumen height against egg weight, making it a destructive test only usable on small samples. NIR spectroscopy can predict the HU value directly from a non-destructive scan of the intact egg, because as an egg ages, the moisture, CO2 and protein structure inside it change in ways that show up in the near-infrared spectrum15.
  • Estimating storage age in days: NIR models can also predict roughly how many days an egg has been stored (studies have tracked eggs from day 0 out to day 21 to 25 of storage)16, which is useful for quality control at packing stations and distribution centers, and can also serve as a check against mislabeled “best before” or production dates.
  • Fraud and mislabeling detection: related spectroscopic work has also been used to verify claims printed on egg labels, such as the declared housing system (free range, barn, caged) or the declared storage duration, flagging cases where the physical egg does not match what the label states.
  • On-line, real-time screening: because these are point measurements rather than full destructive tests, low-cost portable NIR sensors can be integrated into packing line equipment for continuous, real-time screening of a much larger share of eggs than manual HU sampling allows.

5. References

  1. What happens with male chicks in the egg industry? RSPCA Australia Knowledge Base. Available from: kb.rspca.org.au
  2. Active sampling of volatile chemicals for non-invasive classification of chicken eggs by sex early in incubation. PLOS ONE. 2023. Available from: PMC10202283
  3. Inside the Egg Industry: Mercy For Animals Investigation Documents the Killing of Newly Hatched Male Chicks. Mercy For Animals. Available from: mercyforanimals.org
  4. EggXYt: A novel approach for sexing chicken embryos on day one before incubation – saving them from being hatched and disposed. CORDIS EU research information. Available from: cordis.europa.eu
  5. Dutch Government Announces Roadmap to End Chick Culling by 2026. Innovate Animal Ag. Available from: innovateanimalag.org
  6. Ending male chick culling: The economics driving Europe’s poultry shift. The Poultry Site. Available from: thepoultrysite.com
  7. Morphology-Based In-Ovo Sexing of Chick Embryos Utilizing a Low-Cost Imaging Apparatus and Machine Learning. Animals (MDPI). 2025. Available from: PMC11816025
  8. The Chicken Genetic Family Tree. Layer Resources. Available from: layer-resources.com
  9. Nociception in chicken embryos (preprint). bioRxiv, doi:10.1101/2020.03.23.003301. Available from: biorxiv.org
  10. Nociception in Chicken Embryos, Part II: Embryonal Development of Electroencephalic Neuronal Activity In Ovo as a Prerequisite for Nociception. Animals (MDPI). 2023. Available from: PMC10525651
  11. When do chick embryos feel pain – and why does it matter? The Poultry Site. Available from: thepoultrysite.com
  12. Saeys W, et al. In ovo sexing of eggs from brown breeds with a gender-specific color using visible-near-infrared spectroscopy: effect of incubation day and measurement configuration. Poultry Science. 2022. Available from: PMID 35339934
  13. Meissner S, et al. In-ovo sexing of 14-day-old chicken embryos by pattern analysis in hyperspectral images (VIS/NIR spectra): A non-destructive method for layer lines with gender-specific down feather color. Poultry Science. 2017. Available from: PMID 27591278
  14. Yang C, et al. A review of the recent advances for the in ovo sexing of chicken embryos using optical sensing techniques. Poultry Science. 2023. Available from: PMID 37480656
  15. Non-Destructive Measurement of Egg’s Haugh Unit by Vis-NIR with iPLS-Lasso Selection. Foods. 2023. Available from: PMC9818847
  16. NIR Spectroscopy for Freshness Detection and Classification of Chicken Eggs. Springer. Available from: Springer chapter