New method casts light on a chicken-and-egg problem

For chickens bred to lay eggs, being male is a gloomy prospect. These cockerels develop too slowly to be raised for meat, so they are usually killed within days of hatching by methods including gassing and grinding.

The practice culls billions of chicks each year, raising ethical concerns. As a result, both United Egg Producers, the U.S. industry group that represents most hatcheries for egg-laying hens, and the German government have pledged to end the practice.

Now researchers have developed an approach that uses spectroscopy to identify the sex of a developing chicken embryo while it’s still in the egg (Anal. Chem. 2016, DOI: 10.1021/acs.analchem.6b01868). The method could allow hatcheries to cull male chick embryos just three days into development, before they are sensitive to pain.

Currently, experts visually determine the sex of chicks after they hatch. Chick sex can also be determined before hatching by sampling hormone levels or DNA from within the egg after removing a piece of shell. But hormone analysis occurs after developing chicks are sensitive to pain, and both methods require sampling and chemical analysis, which may not be feasible on an industrial scale.

Roberta Galli of Dresden University of Technology and colleagues thought Raman spectroscopy might be able to determine sex in a less invasive way, from embryo blood: Male blood has different protein and sugar profiles and about 2% more DNA than female blood.

The team uses a laser to remove a 15-mm-diameter piece of shell, revealing the embryo’s blood vessels. On day three of development, the researchers shine near-infrared laser light on the vessels, collect a Raman spectrum, and then assign a sex based on algorithms they developed.

For 101 eggs whose sex was also determined by DNA test, the algorithm correctly identified embryo sex in 90% of cases. Galli says improvements to the technique since her team’s initial report have increased the accuracy to 95%—closer to the 98% accuracy of expert sexers in industry.

After the analysis, the researchers close up the egg with surgical tape and allow it to grow. About 81% of the eggs they tracked after the test hatched and developed normally, compared with 92% of control eggs.

The team’s lab system can process two to three eggs per minute—much slower than expert chick sexers, who can work at five to eight times that rate. But the team is building an industrial prototype to automate the process and has partnered to test it with a major commercial producer of egg-laying hens in Germany.

Rodrigo Gallardo, an expert in poultry biology at the University of California, Davis, calls the technique “very promising,” but use in the poultry industry will require lowering the processing time, improving the accuracy, and ensuring that the method does not harm or contaminate developing chicks.