At a hatchery in the Netherlands that supplies the egg industry with laying hens, a machine inserts needles into rows of chicken eggs that shuttle down a conveyor belt, drawing a tiny drop of liquid from each egg before plugging the holes in the shells with biodegradable glue. The fluid is quickly analyzed for the big reveal: male or female.

Male eggs are discarded. The female ones are incubated and hatched.

Not long ago, it was impossible to know the sex of a chicken in an egg. As a result, an estimated six billion newly hatched male chicks are killed world-wide each year, according to the Foundation for Food & Agriculture Research, which is funded by the U.S. government. The male chicks are useless to hatcheries because they don't lay eggs and don't gain weight as quickly as the type of chickens raised for slaughter. Some baby chicks, while still alive, are chopped up with rotating blades in maceration machines and others are gassed with carbon dioxide.

A wave of new technologies aims to end the killing by figuring out the sex of the chicken before it hatches. Concern over the fate of male chicks is growing in some western countries, with governments in Germany and elsewhere taking steps to end or limit the practice. Some retailers are trying to get ahead of the issue, pushing their suppliers to introduce technology that allows for sex sorting in the egg. Take-up has been limited so far, as new methods can be costly, or only work on eggs from certain types of chickens.