A sow in a farrowing crate. They have been approved for use in New Zealand in spite of welfare concerns.

Pig farrowing crates that have created welfare concerns are here to stay.

The farrowing crates keep sows in confined pens and they are unable to turn around, but allow their piglets to move.

The review of farrowing systems by the National Animal Welfare Advisory Committee (NAWAC) has found that the use of farrowing crates was the best system available.

Last year, NAWAC was asked to review the use of farrowing crates by the Minister of Primary Industries.

NAWAC's review included an assessment of New Zealand and international research and practice, an examination of international standards and New Zealand's Animal Welfare Code.

The welfare committee review states: "NAWAC does not consider that there is any practical alternative system that provides comparable levels of piglet welfare while better meeting the welfare needs of sows."

Massey University PhD student in pigs, Kirsty Chidgey​ said she was not surprised by the decision that farrowing crates were the option chosen by NAWAC.

She said she had studied alternatives to the crates.

"There are farrowing pens, which give the sow more room. And there is the option of letting the sow out of the farrowing pen when the piglets are three days old."

But she says it is always a trade off between the needs of the sow and piglet survival.

Chidgey said research showed the highest piglet survival was when the sow was confined in a farrowing crate, but that compromised the sows' needs.

She said no country had banned farrowing crates, but there were limits to the time a sow could be confined.

Chidgey said piglet death was higher in pens and in outdoor systems.

"NAWAC said it was best for a sow in an outdoor system, but more piglets died".

She said piglet mortality indoors was about 10-12 per cent for farrowing crates. But their mortality in pens was 14-16 per cent, and outdoors about 18 per cent of piglets died.

"You can improve it for the sow, but at the expense of the piglets. And that's an animal welfare and economic issue too."

Chidgey said the heaviest sow she had weighed was 428 kilograms which had 18 piglets a few days later.

"She probably lost 40kg with those piglets' births. But is shows the disparity between the huge sow and piglets at birth."

NZPork chairman Ian Carter welcomed NAWAC's decision.

"Farmers care for their animals. We know that our specialist farrowing systems are the best way to look after the welfare of sows and piglets around the time the piglets are born and up until weaning," he said.

"There are many factors involved in caring both for the sow and her piglets through this critical period including providing security for the mother, optimal feed and water without competition from other sows, and maintaining the environment at her preferred temperature range. The newborn piglets need a warm, dry, hygienic environment that provides good access to their mothers' teats to give them the best start in life."

Carter said without crates, the piglet mortality rate would be higher.

He said NAWAC's review also encouraged the industry to look for innovative solutions and work towards alternatives.

"These systems will further evolve as knowledge and science continue to develop. As farmers we spend a lot of time understanding and working with our animals to develop systems that provide for their needs."