Sexing chicks: How genetically modified female-only chickens could transform the egg industry
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In our previous episode, we were talking about the ethics of genome modification, and one of the areas of debate was the use of CRISPR to edit the genes of farm animals. We’ve been tinkering with genomes for as long as farming has existed purely by selective breeding; domestication is by definition the process of breeding animals with desirable genes, but at the end of last year, researchers in Israel made a pretty major gene editing breakthrough: female-only chicks.
One of the major ethical concerns with the egg industry is that only female chickens lay eggs, but 50% of chicks are male. Right now, there are people in the world with the title of “chick sexer” whose job it is to identify males from females when the chicks are only a day old. It’s a highly skilled job that involves gently squeezing the cloaca or ‘business end’ of a chick and seeing if a male ‘bump’ is present. It apparently takes 3 years to train as a chick sexer and you’re expected to be able to sex about a thousand chicks an hour, or one chick every four seconds with a 98% accuracy rate, so it’s not for the faint hearted. In 2015 there was even a chick sexer shortage in the UK (I can’t possibly imagine why) and the poultry industry were offering salaries of forty thousand pounds a year.
The reason why sexing chicks is so valuable to the egg industry is of course because male chickens don’t lay eggs, so poultry farmers don’t want to spend money feeding and housing males for any longer than they have to. As a result, an estimated 29 million male chicks are killed every year in the UK alone.
As a way to improve animal welfare in the poultry industry, a team of researchers at the Volcani Institute near Tel Aviv, lead by embryologist Dr Yuval Cinnamon, have come up with a clever genetic technique to prevent male chicks from hatching. Now as you can imagine, if this technique works, it will be worth billions to the egg industry so for now the specifics are being kept under wraps as the team plan to licence the technology, but here’s what we know so far about how it works.
Chickens, like all birds, use the ZW sex chromosome system. If you think about this from the chick’s perspective, you’re always going to inherit a Z chromosome from your ZZ father. If you’re a ZW female chick, you inherit a W chromosome from your mother and if you’re a ZZ male chick, you inherit a Z chromosome from your mother.
What Cinnamon’s team have done is they’ve created a modified version of the Z chromosome where if you shine blue light on a developing egg and it has this modified version, the embryo stops developing. So if all the mother hens have modified Z chromosomes, all of their sons and none of their daughters will inherit the modified form. So you can shine a blue light on all the eggs and only the male ones will stop developing,with all of the resulting hatchlings being female future egg-layers. You’ve got to admit, it’s an ingenious solution.
If you’re following along at home, you’ll have spotted that the female chicks that are born don’t inherit the modified Z chromosome, which is good news if for whatever reason you’re worried about eating modified DNA, but bad news if you’re a farmer who wants to use some of those females to produce the next generation of egg layers, as you’re back to square one with your chicken sexing problem unless, presumably, you buy in more genetically modified breeding stock.
As with many advances in genetically edited crops and animals, there’s always the risk that this technology could funnel profits into the hands of a small number of companies. And if this technology is only available in a small number of chicken breeds, it could reduce the genetic diversity of farmed chickens worldwide, which is never a good thing when we seem to face wave after wave of bird flu and other infectious diseases.
But this is still some pretty cool science that could have massive welfare implications for the farming industry, preventing billions of male chicks being culled each year by altering their genetics so that males are never born at all.
https://www.bbc.co.uk/news/science-environment-63937438
https://kb.rspca.org.au/knowledge-base/what-happens-with-male-chicks-in-the-egg-industry/
