Is it possible to change a chicken’s sex before it hatches?
The eggs we eat have a hidden cost. About 7bn male chicks are killed worldwide every year to produce them. Farmers need to replenish their supply of egg-laying hens but, by nature, half the chicks that hatch are male and growing them for meat is uneconomic – that industry uses faster growing breeds. In many countries they are tossed into shredding machines, although in the UK they are gassed.
But what if those male chicks could instead hatch out as functional females, able to grow into egg-laying birds? That’s the vision of Israeli startup Soos Technology. Founded in 2017, the company, which has received $3.3m in investment and prize winnings, wants to make commercial hatcheries kinder and more economic by changing the effective sex of poultry embryos as they develop.
Its technology exposes eggs to sound vibrations which, it says, alters the gene expression in developing male embryos, so rather than testes, an ovary forms instead (birds have only one). The company says its experiments are currently producing batches of chicks where 60% are observably female and it expects this to increase. “We are changing the sex of the chicken to dramatically decrease male chicks culled,” says Yael Alter, Soos’s CEO. Even if all male chicks aren’t converted, it could still make a difference. The company is currently piloting its technology at a commercial egg farm in Israel and has other pilots lined up with an Italian and a US egg producer.
Other startups are also working to solve the male chick problem. But they are focused on detecting egg sex prior to hatching, so the male eggs can be removed from incubators and disposed of earlier. Techniques include sampling the egg fluid and optical technologies to see inside. Hatcheries are looking to these as some European governments are trying to put an end to killing male chicks – including France by the end of 2021. Alter says Soos’s technology transforms eggs, so they don’t need disposal.
The idea that sound could be used to change the functional sex of chickens might seem far-fetched. But another external environmental factor, temperature, determines sex in many reptiles and some fish – though this does not apply in birds. And there is science that indicates gene expression can be influenced by sound. It was recently shown that when some types of cultured mouse cell 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 biostimulation source at cellular level that triggers gene responses,” says Masahiro Kumeta, a researcher at Kyoto University in Japan pioneering this work.
Alter is vague about how her co-founder, Nashat Haj Mohammad, stumbled on to sound. He found eggs laid in certain areas of his family’s small free-range chicken farm seemed to yield more female chicks.
Soos uses speakers to transmit sound to the eggs in the first 13 days of incubation, converting a standard commercial egg incubator into an acoustic one to do so. It is a loud continuous beeping noise audible to the human ear that plays several hours a day. Most important are the frequency and volume, and other factors such as temperature and humidity are controlled, explains Alter, adding that Soos is seeking patents for the method.
Alter says Soos has treated batches of thousands of eggs at a time and “over and over” achieved a 60%-plus female skew that has risen to 70% in some areas of the incubator. Calculations are based on visually sexing the chicks that hatch and retaining those determined to be female. Their DNA is then randomly sampled, finding the presence of some genetic males. Mostly the chicks aren’t kept more than 30 days, but 1,500 chicks, determined by sexing to be female, were grown two years – long enough to lay eggs. The genetic males appeared to lay at the same rate – the group didn’t produce fewer eggs overall than would be expected – and the treatment didn’t do any harm in other ways.
Soos speculates that sound suppresses the expression of the DMRT1 gene – widely accepted to be responsible for sex development in poultry. Like humans, birds carry a pair of inherited 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 testis formation while the single dose in female embryos leads to ovary formation. However, if DMRT1 is suppressed in male embryos, it shrivels one testis and allows the other to develop as an ovary. “You can change the phenotype in birds,” says Alter, though she adds that Soos doesn’t know exactly how the sound achieves it.
Developmental biologists studying chickens find it surprising that Soos’s “reversed” birds would look female and lay eggs, however. Research shows you can’t just manipulate DMRT1 in chickens and get a perfect female, according to Mike Clinton at the University of Edinburgh’s Roslin Institute and Craig Smith of Monash University in Melbourne, Australia.
First, they note that a genetically male bird transformed by reducing DMRT1 so it developed an ovary would still look like a male bird: with more muscle, male feather patterns and bigger wattles and spurs. That is because birds seem to be less influenced by gonadal hormones, which in mammals masculinise or feminise the body after testes or ovaries have formed. Chicken cells have been shown to “know” innately whether they are genetically male or female, independently of hormones. “You can get males that have ovaries after modulating DMRT1, but the rest of the bird is still male,” Smith explains.
Second, a recent study by Clinton, not yet published, demonstrates that genetically male birds whose sex is “reversed” after reducing DMRT1 when they are embryos do not lay eggs. “We think the male brain does not provide the appropriate signals to the ovary,” says Clinton.
Kristen Navara, a poultry scientist at the University of Georgia in the US notes a 60% skew could happen by chance depending on sample size. “The company needs studies that are peer reviewed,” she says.
Soos acknowledges more testing is needed. “We are working towards publishing,” says Rotem Kadir, Soos’s scientific director. He notes that while the DMRT1 gene is the prime candidate for how the sound has an effect, it isn’t certain. “There could be other genes,” he says.
Soos is planning experiments in chicken cell cultures this year to try and elucidate the mechanism of the effect. But the focus at the moment is on increasing the number of females in each hatching cycle by developing a system to improve how sound is transmitted in the incubator, so each individual egg “hears” it at the same, optimal volume.
Both the campaign group People for the Ethical Treatment of Animals (Peta) and the producer’s group the British Egg Industry Council (BEIC) agree that if the technology is effective, it could be useful. Though Peta says it still won’t make eating supermarket eggs ethical because hens are still being exploited. The BEIC stresses that culled male chicks aren’t wasted – they are in high demand as a food source for reptiles and birds of prey in zoos and kept privately.
Alter knows what she would like stamped on egg boxes one day: “No male chicks killed to produce these eggs,” she says. “It is important for consumers to know.”