The investigations involved incidents at piggeries in Christchurch and Kumeu. Both involved video footage gathered by a third party.

MPI Director Compliance Dean Baigent said in both cases there was insufficient evidence to prove offences.

Christchurch Investigations

Mr Baigent said with the Christchurch incident there had been a two month delay in taking the footage and MPI becoming aware of it when it featured on television.

"The Christchurch footage showed a rat infestation, dead piglets and a dead pig. There was no evidence of that when compliance officers investigated.

"The owner had undertaken pest control, between when the footage was taken and MPI visited, which was the day after MPI learned about the incident.

"Two independent vets viewed all the footage made available by the complainants and were unable to conclude that the the rats had caused harm to the pigs, or establish how the adult pig and the piglets had died.

Mr Baigent said MPI have regularly inspected the piggery since the investigation and have not found any material animal health or welfare issues.

"This is an old and dated piggery which is coming to the end of its economic life. Some of the older buildings shown in the footage are no longer in use by the farmer."

Kumeu Investigation

Mr Baigent said there was insufficient evidence to prosecute the Kumeu incident of footage of a pig being euthanised and piglets being loaded onto a truck.

"Two independent vets viewed the footage They were unable to conclude that the pigs suffered unnecessary pain or distress or ill treatment. As a result the footage failed to provide sufficient evidence for a prosecution.

"The person who took the footage declined to provide a statement for continuity of evidence."

MPI investigators visited the piggery and found no animal welfare concerns.

Mr Baigent said the footage of both incidents was very distressing for viewers.

"We completed a thorough investigation of both incidents with the help of independent vets who are experts in pig veterinary science. We did not find evidence to prove animal welfare offending beyond a reasonable doubt."

Mr Baigent said MPI takes animal welfare very seriously.

"When we find evidence of offending we put those responsible before the courts. The maximum penalties are very significant, five years in prison and a $100,000 fine for individuals."

MPI had 28 successful animal welfare prosecutions in 2013.