Is it possible to change the sex of a chicken before it is born? | Eggs

The eggs we eat have a hidden cost. Around 7 billion male chicks are killed worldwide each year to produce them. Farmers need to replenish their supply of laying hens but by nature half the chicks hatched are male and raising them for meat is not economical: that industry uses faster growing breeds. In many countries they are thrown into shredders, although in the UK they are gassed.

But what if those male chicks could instead hatch as functional females, capable of becoming egg-laying birds? That’s the vision of Israeli startup Soos Technology. Founded in 2017, the company, which has received $3.3 million in investment and awards, wants to make commercial hatcheries kinder and cheaper by changing the effective sex of poultry embryos as they develop.

His technology exposes the eggs to sound vibrations which, he says, alters gene expression in developing male embryos, so that instead of testicles, an ovary is formed (birds only have one). The company says that its experiments are currently producing batches of chicks where 60% are observable females and it expects this to increase. “We are changing the sex of the chickens to drastically reduce the culling of male chicks,” says Yael Alter, CEO of Soos. Even if all the male chicks don’t convert, it could still make a difference. The company is currently testing its technology at a commercial egg farm in Israel and has other pilots lined up with an Italian and American egg producer.

Other startups are also working to solve the male problem. But they focus on detecting the sex of the egg before hatching, so the male eggs can be removed from the incubators and discarded sooner. Techniques include taking samples of the egg fluid and optical technologies to see inside. Hatcheries are looking to this as some European governments are trying to end the killing of male chicks, including France by the end of 2021. Alter says Soos’ technology transforms the eggs, so they don’t need to be disposed of.

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The idea that sound could be used to change the functional sex of chickens may seem far-fetched. But another external environmental factor, temperature, determines sex in many reptiles and some fish, although this does not apply to birds. And there is science indicating that gene expression can be influenced by sound. It was recently shown that when certain types of cultured mouse cells were bombarded with sound emissions, genes involved in bone formation and wound healing were suppressed. “It is not yet widely accepted, but sound can be a source of biostimulation at the cellular level that triggers genetic responses,” says Masahiro Kumeta, a researcher at Kyoto University in Japan who pioneered this work.

If DMRT1 is suppressed in male embryos, one testicle withers away, allowing the other to develop as an ovary.

Alter is vague about how her co-founder, Nashat Haj Mohammad, stumbled upon the sound. He discovered that eggs laid in certain areas of his family’s small free-range chicken farm seemed to produce more female chicks.

Soos uses speakers to transmit sound to the eggs in the first 13 days of incubation, turning a standard commercial egg incubator into an acoustic one to do so. It is a loud continuous beep audible to the human ear that sounds for several hours a day. The most important are frequency and volume, and other factors such as temperature and humidity are controlled, Alter explains, adding that Soos is seeking patents for the method.

Alter says Soos has treated batches of thousands of eggs at a time and “time and time again” achieved a female bias of over 60% which has risen to 70% in some areas of the hatchery. Calculations are based on visual sexing of hatched chicks and retention of those determined to be female. Their DNA is then randomly sampled, finding the presence of some genetic males. Most chicks are kept no more than 30 days, but 1,500 chicks, determined by sex to be female, were raised for two years, long enough to lay eggs. The genetic males seemed to lay at the same rate, the group produced no fewer eggs overall than expected, and the treatment did no harm in other ways.

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Soos speculates that the sound suppresses the expression of the DMRT1 gene, widely accepted as responsible for sexual development in poultry. Like humans, birds carry an inherited pair of sex chromosomes that determine their genetic sex. But in the avian system, ZZ is male and ZW is female. A gene on the Z chromosome, DMRT1, regulates gonad development. The double dose in male embryos leads to the formation of testicles, while the single dose in female embryos leads to the formation of ovaries. However, if DMRT1 is suppressed in male embryos, one of the testes shrivels up, allowing the other to develop as an ovary. “You can change the phenotype in birds,” Alter says, though he adds that Soos doesn’t know exactly how he achieves the sound.

However, developmental biologists who study chickens are surprised that Soos’s “inverted” birds look like females and lay eggs. Research shows that you can’t just manipulate DMRT1 in chickens and get a perfect female, according to Mike Clinton of the Roslin Institute at the University of Edinburgh and Craig Smith of Monash University in Melbourne, Australia.

First, they note that a genetically male bird transformed by knocking down DMRT1 to develop an ovary would still look like a male bird: with more muscles, masculine feather patterns, and larger wattles and spurs. This is because birds appear to be less influenced by gonadal hormones, which in mammals masculinize or feminize the body after the testicles or ovaries have formed. Chicken cells have been shown to innately “know” whether they are genetically male or female, independent of hormones. “You can get males that have ovaries after you modulate DMRT1, but the rest of the bird is still male,” Smith explains.

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Second, a recent, as-yet-unpublished study by Clinton demonstrates that genetically male birds whose sex is “reversed” after DMRT1 reduction as embryos do not lay eggs. “We think the male brain is not providing the proper signals to the ovary,” Clinton says.

Eggs hatched inside an incubator at an agricultural fair in Paris.  France will ban the killing of male chicks from the end of this year.Eggs hatched inside an incubator at an agricultural fair in Paris. France will ban the killing of male chicks from the end of this year. Photograph: Joel Saget/AFP via Getty Images

Kristen Navara, a poultry scientist at the University of Georgia in the US, notes that a 60% bias could occur by chance depending on the sample size. “The company needs peer-reviewed studies,” she says.

Soos acknowledges that more testing is needed. “We are working to publish,” says Rotem Kadir, Soos’ scientific director. He points out that while the DMRT1 gene is the leading candidate for how sound has an effect, it’s not certain. “There could be other genes,” he says.

Soos is planning experiments in chicken cell culture this year to try to elucidate the mechanism of the effect. But the focus right now is to increase the number of females in each hatching cycle by developing a system to improve the way sound is transmitted in the incubator so that each egg “hears” it at the same optimal volume. .

Both the People for the Ethical Treatment of Animals (Peta) campaign group and the British Egg Industry Council (BEIC) producer group agree that if the technology is effective, it could be useful. Though Peta says she still won’t make eating supermarket eggs ethical because the chickens are still being exploited. The BEIC emphasizes that culled male chicks are not wasted: they are in high demand as a food source for reptiles and birds of prey in zoos and are kept privately.

Alter knows what she’d like to stamp on the egg cartons one day: “You don’t kill male chicks to produce these eggs,” she says. “It’s important that consumers know this.”

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