New Zealand is in the grip of an egg shortage as the industry undergoes a massive period of disruption while it transitions to free-range farming.

The shortage has also been caused by an increased appetite for eggs, with New Zealanders consuming 230 eggs per person last year, compared with 200 per person a decade ago.

But the main problem is farmers struggling to modify their operations and maintain output as the industry moves from cage to barn and free-range egg production.

Over the past few years all of New Zealand’s major supermarket brands have committed to stop selling caged eggs by 2027, as have a number of major food service providers, and fast-food chains including McDonalds and Burger King.

The increased demand for barn and free-range eggs has caused occasional shortages in egg supply, said Nikhil Sawant, a Countdown supermarket spokesperson.

“We’re working closely with our egg farmers as we all adjust to this increased demand, but there are unfortunately going to be shortages from time to time. We’re trying our best to keep shortages to a minimum and are expecting supply to improve in the coming few months.”

Michael Brooks, executive director of the Poultry Industry Association of New Zealand, said supermarkets were struggling to get the volumes of eggs they required as the nation’s hen flock had decreased from 4.2m birds in 2018 to around 3.6m this year.

The decrease comes as farmers search for new land and infrastructure to build much larger free-range farming operations.

Some farmers were experiencing high levels of stress and anxiety at the rapid pace of the change, with others quitting the industry for good, Brooks said.

“If you are looking at moving to free-range or even barn, you are basically looking at an entirely new farm, there’s a huge amount of pressures on farmers right now.”

“Supermarkets are maybe struggling to get the volumes they’d like”.

Brooks said farming free-range was more complex for farmers as they had to deal with issues such as weather, contamination of feed supply, diseases and a higher mortality rate among birds – which all contributed to a minimum 50% higher egg cost for consumers.

A dozen free-range eggs cost NZ$7 and up at most supermarkets, while 30 caged eggs sell for NZ$9.5.

Antoinette Laird, head of external relations for Foodstuffs New Zealand, said in a statement that while they weren’t facing any imminent shortages “there is a definite increase in demand for cage-free eggs as customers become increasingly concerned about animal welfare.”

According to Consumer New Zealand at least three quarters of New Zealanders buy cage-free “at least some of the time”, while more than a quarter purchase free-range exclusively.

Companies selling free-range eggs have doubled since 2010, but there are concerns there is still no standard definition of what free-range means.

In 2017 an investigation by Newsroom found millions of free-range eggs sold at Countdown supermarket actually came from caged hens.

In the European Union battery cages began to be phased out in 2012, while Switzerland was the first country in the world to ban them outright in 1992.