Read our COVID-19 research and news.

New technologies for identifying male embryos while still in the egg could avert culling.


‘Ethical’ eggs could save male chicks from mass slaughter

In hundreds of grocery stores here, shoppers can pay a few extra cents for eggs stamped with a heart and the word respeggt—to show that they were laid by hens that did not hatch alongside male chicks destined for slaughter. This week, the eggs will be available for the first time in stores outside of Berlin. By the end of the year, they will appear all across Germany—a sign that scientists are getting closer to solving a tricky chick-and-egg problem.

Modern laying hens have been bred to produce huge numbers of eggs, but their brothers are useless. They don't put on weight fast enough to be raised for meat. So hatchery workers—specialized "sexers"—sort day-old chicks by hand, squeezing open their anal vents for a sign of their sex. Females are sold to farms. Males—roughly 7 billion per year worldwide, according to industry estimates—are fed into a shredder or gassed.

Sorting males from females before chicks hatch at 21 days wouldn't just avoid the massacre. Hatcheries would no longer need to employ sexers, they wouldn't waste space and energy incubating male eggs, and they could sell those eggs as a raw material for animal feed producers, the cosmetics industry, or vaccine manufacturers. The United Egg Producers, a U.S. cooperative, says it wants to be cull-free by 2020, and the German government has said it will outlaw the practice. "Everyone wants the same thing, and the right piece of technology could solve this right now," says Timothy Kurt, scientific program director at the U.S. Department of Agriculture's Foundation for Food and Agriculture Research (FFAR) in Washington, D.C.

One contender is the technology behind the respeggt eggs, which sorts them based on sex hormones. Funding from governments and industry has prompted an abundance of other ideas—from laser spectroscopy to MRI scans to genetic engineering. And next month, FFAR will announce seed funding for six finalists—selected from 21 entries from 10 countries—for an Egg-Tech Prize competing for up to $6 million for a workable method.

Almuth Einspanier, a veterinary endocrinologist at Leipzig University in Germany, and her colleagues laid the groundwork for the respeggt brand. They found that by day 9 of development, female embryos produce a hormone called estrone sulfate that can be detected reliably in fluid that builds up in the egg—"essentially the embryo's pee," Einspanier says. The German grocery chain Rewe and HatchTech, a Dutch hatchery equipment supplier, founded Seleggt, a spin-off based in Cologne, Germany, to market the technique. The company built a robot that fires a laser to open a hole in the shell much smaller than a pinhead. It sucks out a minuscule drop of the fluid and adds it to a solution that turns blue in the presence of the female hormone. Female eggs go to the incubator and male eggs are sent off to be frozen and processed into powder for animal feed.

Ludger Breloh, Seleggt's managing director, says that the system is sorting up to 3000 eggs an hour in a Dutch hatchery. As those hens reach laying age, Seleggt will be able to supply eggs to more than 5000 grocery stores across Germany. But large hatcheries process as many as 50,000 eggs an hour, which would overwhelm the current system. Some animal welfare advocates raise a more fundamental problem, claiming that a 9-day embryo might feel pain. And hatcheries must pay for 9 days of incubation costs.

Chickens have been genetically engineered to produce male eggs that are fluorescent.

Danni Offen/EGGXYT LTD.

Gerald Steiner, an expert in medical imaging at the Technical University of Dresden in Germany, helped find a test that works at day 4. His team shines a laser through a thumbnail-size hole in the eggshell and measures fluorescent signals from the blood cells. The signals are different for male and female embryos, likely because males develop slightly faster and form certain blood cells sooner. In female eggs, the hole is sealed with medical tape, and the egg is returned to incubation. The group is working with Agri Advanced Technologies (AAT), a German subsidiary of one of Europe's largest chicken breeders, to develop a prototype system. So far, says Jörg Hurlin, managing director at AAT in Visbek, sorting accuracy is high, but "we are not yet where we need to be."

Ovabrite, a U.S company in Austin, is chasing a technique that would leave the eggshell intact and sort eggs before incubation. Mass spectrometers would capture and analyze sex-specific volatile molecules that leak through the eggshell. Scientists suspect the molecules, first discovered in quail eggs, may allow parent birds to smell clues about an embryo's development and sex. But it is still a challenge to reliably detect such a faint signal from preincubation eggs, which must be refrigerated, says Ovabrite President Jonathan Hoopes.

Some predict that genetic engineering could help do away with complicated robots. Groups in Australia and Israel have used the CRISPR gene-editing technique to modify hens' sex chromosomes so that their sons carry a marker gene that makes male eggs glow under fluorescent light. That would allow hatcheries to sort out the fluorescent male eggs with a simple detector. Finding a marker that produces a strong enough signal in early embryos is a challenge, says Yehuda Elram, CEO of eggXYt (pronounced "exit") in Jerusalem. He says eggXYt has found a solution, but declined to say whether it is close to hatchery tests.

Public opposition to genetic modification in Europe means the approach is unlikely to catch on there. But Mark Tizard, a geneticist at the Australian Animal Health Laboratory in Geelong, who is also working on the technology, says his group's social science research suggests consumers in North America and Australia might accept it. Neither the layer hens nor the eggs sold for consumption would contain modified genes, because only males carry the inserted marker gene, he notes.

Other noninvasive ideas are still in the running: Scientists in Turkey reported that with the help of machine learning they could detect subtle differences between male and female egg shapes. German researchers have examined MRI scans of intact eggs for sex differences.

Meanwhile, the political pressure continues. In June, a German court ruled that culling day-old chicks violates the country's laws against killing animals without a justifiable reason. The court allowed hatcheries an exception "until a feasible alternative is available," but politicians are still considering a law to ban culling.

Researchers, feeling they are close to commercial breakthroughs, don't want that to happen—yet. "A ban now would do more harm than good," Einspanier says—mostly by driving hatcheries to neighboring countries with less strict laws. With a bit more time, she says, her field should be able to finally crack the problem.