Ministry of Agriculture and Forestry investigators say a piggery belonging to a former pork industry board chairman is not breaking any animal welfare laws.

MAF investigations manager Greg Reid told Newstalk ZB the ministry could only take action if specific animals were suffering unnecessarily or if the pigs had untreated diseases.

He expected the case to trigger a review of regulations for operating pig farms.

The farm had also been investigated three years ago, and cleared of any wrong-doing.

Later today, National Animal Welfare Advisory Committee members would discuss the future of sow crates, used in pig farms.

Colin Kay's Kuku Beach Rd piggery at Ohau, near Levin, was the subject of TVNZ's Sunday programme in which animal welfare activists took comedian Mike King to the plant to highlight the pigs' alleged poor treatment.

Mr Kay, a former NZ Pork Industry Board chairman, said a Ministry of Agriculture and Forestry inspector and an independent veterinarian yesterday found "no issues whatsoever".

"It complies with the [animal] welfare code so I'm quite happy," he said.

Mr Kay, whose Kuku Beach Rd plant was investigated in 2005, said he was "very upset" by the break-in to his plant.

Save Animals From Exploitation (SAFE) national director Anthony Terry said the lack of immediate findings from MAF's investigation was not surprising but upsetting "because the conditions in there are grossly inadequate".

NZ Pork chairman Chris Trengrove said the Sunday footage was emotive and while "not a good look" for Mr Kay's pig farm was an unfair portrayal of the industry.

He said while locally produced free-range pork made up about 45 per cent of the market, for intensive pig farmers making the change was not easy. It would cost about $5000 per sow to start from a green-field site, he said.

"So you can understand that when you are flooded with imported pork it is pretty hard for farmers to make that change."

But Canterbury free-range pig farmer, Linda McCallum-Jackson, said this was "a load of twaddle".

A more accurate cost for a breeding sow to go free range was about $1300. Her 90 sows had several hectares to roam in and although they produced fewer piglets in their first year of breeding their young were healthier.

RSPCA chief executive Robyn Kippenberger also doubted Mr Trengrove's claims and said New Zealanders would be willing to pay more for pork if they knew the animals had been farmed humanely.

* Price to pay

Pork rack
- Regular $19.99/kg
- Free range $29.99/kg
Pork loin chops
- Regular $16.49/kg
- Free range $22.99/kg
Champagne ham
- Regular $17.90/kg
- Free range $28.99/kg
Middle bacon
- Regular $19.93/kg
- Free range $35.30/kg

Source: New World Victoria Park