Chicken sexers in Japan once enjoyed well-paid careers with overseas travel and job security, according to the Poultry Highlights newsletter from the National Farmers Union. However, industry changes mean their expertise is not needed so widely and less people are seeking to join the profession.

Chicken sexers can manually sort poultry at a speed of 8,000 chicks per day and 99.7 per cent accuracy by learning to identify the external appearance of the birds' sexual organs.

Most experts in vent (or cloaca) sexing come from Japan, where the method of distinguishing patterns of birds' sexual organs at one day-old was invented in 1933 and helped revolutionise the poultry business, with Japanese sexers in demand internationally for their skills.

But as Japan's youth migrates to cities, fewer people want the job. "I just got two emails from Denmark and Hungary asking to send over Japanese experts but I have nobody at hand," said Atsushi Nodera from Japan Livestock Technology Association, a sexer with over 30 years experience.

"Young people now want a degree and to become a doctor. The effect is that we have plenty of jobless doctors and no one to carry on our profession," added Nodera who spent 10 years in Spain and Germany working as a chick sexer.

But the poultry industry is also changing, with chicken imports eroding the need for sexers at some Japanese hatcheries.

The demand for Japanese experts internationally is also on the decline with more breeders using chickens with feather sexing. This has led to a fall in the number of chicken sexers being trained in Japan, which once boasted a workforce of more than 1,000 sexers but now only has a few hundred.