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But the pork industry's head says the farming method stops sows accidentally killing a third of their litter and must stay.
About 200 people in the Octagon on Saturday attended a national day of action against factory farming.
Protest sign slogans among the crowd included: ''Don't Stomach Cruelty'', ''Meat is Murder'' and ''Pigs Deserve Better''.
Safe members and politicians from the Green, Labour and the InternetMANA parties spoke at rallies in Dunedin, Christchurch, Wellington, Hamilton and Auckland.
At the Dunedin rally were Greens co-leader Metiria Turei, Labour Dunedin South MP Clare Curran and InternetMANA candidate Andrew LePine.
Safe members gathered signatures for a petition asking John Key to end intensive pig farming in New Zealand and to put an immediate phase-out date on farrowing crates.
Safe Dunedin volunteer co-ordinator Leo La delle said he was ''shocked and saddened'' by pig farming in New Zealand and farrowing crates failed to meet the obligations of the Animal Welfare Act, as the sows could not express normal behaviours, such as turning around.
Farmwatch volunteer Carl Scott said farrowing crates were used regularly in Otago, including in Hampden by New Zealand Pork chairman Ian Carter.
Mr Carter, talking to the Otago Daily Times from his pig farm on Saturday, said the slogans used in the Octagon rally revealed an agenda to end to all animal farming, which had great implications for the New Zealand economy.
''This is wider ... than just our industry,'' he warned.
Farrowing crates gave a piglet a 33% higher chance of survival and allowed a sow its ''critical'' needs after giving birth.
The 250kg sows wanted to be in an area secure from predators, where its 1.5kg piglets had access to food, water, warmth and shelter, he said.
''There's a whole lot of reasons we do what we do and largely it is to protect the animal.''
If a sow had too much room to move it would squash many piglets, he said.
Animal welfare groups' desire for pigs to be farmed among ''spring grass and daffodils'' was unrealistic.
''Our animals don't get any nutrient value from grass and piglets are being born nearly every week of the year, so any extreme weather event will compromise our newborns.''
The industry used the term ''farrowing pen'' rather than crate because it restricted just the sow for a time after giving birth.
''More than 90% of the pigs have freedom of movement.''
Farrowing pens were the most commonly used pig-farming system in the world, he said.