Intensive pig farming and the pig code need to change if images shown on a television programme reflect the state of the industry nationally, Prime Minister John Key says.

TVNZ's Sunday programme recently broadcast footage of an animal rights organisation escorting comedian Mike King around a North Island intensive pig farm they had broken into.

King, a long-standing front man for a campaign advertising pork, said he was deeply ashamed of his role.

The pigs were unable to move and obviously in distress, chewing at the cage bars and frothing at the mouth, he said.

In Parliament, Green MP Sue Kedgley asked Mr Key about the case he previously described as `very, very disturbing".

Mr Key said Agriculture Minister David Carter was looking into the issue and the National Animal Welfare Advisory Committee (Nawac) members was considering the 2005 pig code. The SPCA and Federated Farmers were represented on the committee.

"If those images that were displayed on the Sunday programme are in anyway a reflection of the industry in New Zealand then I would expect changes to that code and changes to the industry," Mr Key said.

Ms Kedgley asked why Mr Carter appeared stunned by the images when he knew of the widespread used of sow crates in New Zealand because he had a briefing from animal welfare group, Campaign Against Factory Farming in 2005. He was also given documents on the issue and was sent emails about the issue.

Mr Key said he had confidence in the minister.

In a subsequent statement Ms Kedgley said she doubted Nawac's "ability to make fair and impartial recommendations" because its chairman, retired veterinarian Dr Peter O'Hara, previously said there was no reason to think pigs were unhappy in sow stalls.

Ms Kedgley said he appeared to have already made up his mind.

The Ministry of Agriculture and Forestry is investigating the piggery filmed.

The farm is owned by former New Zealand Pork Industry Board chairman Colin Kay who said the pigs did not normally behave the way shown in the footage.

The New Zealand Pork Industry Board said long-term use of sow stalls was being phased out and the programme did not represent the pork industry as a whole.