Female pigs shouldn't be forced into farrowing crates, according to an animal behaviour expert.
While New Zealand banned sow crates, which kept pregnant pigs confined for weeks, in 2015, farrowing crates are still widely used.
About 60 percent of sows are placed in the rectangular metal cages a few days before giving birth and stay there until their piglets are weaned at about four weeks old.
Former NZ Pork chairman Ian Carter has defended the industry's use of farrowing crates, saying they create an environment "very similar to a maternity hospital".
Save Animals from Exploitation (SAFE) protested the crates at Parliament on Thursday, with campaign manager Marianne Macdonald calling Mr Carter's comment an "absurd comparison".
More than 100,000 people have signed a petition to ban the crates.
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Animal behaviour expert Dr Elsa Flint says sows don't do well in the confined spaces, and often display behaviours indicating stress such as bar biting and chewing.
"These crates are very small and they can't turn around in them so all they can do is stand up, lie down and maintain a posture looking straight ahead. Very small, very restricted movement and they get very frustrated in there."
Pregnant sows experience strong desires to nest in preparation for their babies, which they aren't able to do in farrowing crates.
"With that inability to do what they're very strongly programmed and driven to do, they become even more frustrated," she explains.
The pork industry claims farrowing crates are used to prevent sows from smothering or sitting on their young, but Dr Flint says piglets still get crushed in them.
"A lot depends on the mother. You can select on good maternal behaviour, good mothering, so a lot depends on her ability to be aware of the piglets and move in a way that doesn't crush them."
She says, in an ideal world, all pigs would be free-range, but it might have to be a compromise between ethics and profitability.
"I don't know if [no confinement] is ever going to be acceptable to the New Zealand public and the farming industry."
When asked by host Ryan Bridge why we should care about pigs' wellbeing when we're going to kill and eat them anyway, Dr Flint says it's a matter of principle.
"You have to think about the fact that you want to give animals the best possible life while they are alive and while we're looking after them.
"These sows are producing piglets to be eaten later in life, but they have a few years of producing before that and they should be kept as comfortable as possible."