The "gory and messy" research that involved five live pigs being shot with a 9mm pistol was justified, the National Animal Ethics Advisory Committee says.

The experiment was carried out in 2009, a collaboration between researchers from the University of Otago, the University of Auckland and the Crown-funded Institute of Environmental Science and Research.

WARNING: GRAPHIC IMAGE BELOW

The details of the experiment, an investigation into blood and bone backspatter from gun shots, have just come to light, after the findings were published in the International Journal of Legal Medicine.

Researchers used synthetic models of pig heads, 14 slaughtered pigs and five live pigs in the study.

The live pigs were anaesthetised, but in two instances the pigs began to spasm after they were shot, which nullified a large portion of the data provided.

The research has caused international outrage, with animal rights groups such as PETA, the Human Society, Safe and the New Zealand Anti-Vivisection Society lambasting the study.

Hans Kriek, executive director of SAFE, turned his finger on the National Animal Ethics Advisory Committee, saying the scope of research they were allowing to be approved was too broad.

He said the cornerstone of approval was in the findings benefiting society, a benchmark he thought this experiment failed to reach.

"Pigs have a different skull structure to humans … I would question whether there is scientific validity in this specific experience to be able to compare anything of use.

"Far too many experiments are allowed to carry on that have no benefits for society as a whole."

Massey University professor of Veterinary Neurophysiology Craig Johnson is the deputy chairman of the National Animal Ethics Advisory Committee.

And while he agreed the research was "unpleasant" and "shocking", he said the end results justified the means.

He said there was a difference between "gory and messy" and "cruelty".

"If you you asked me if the research was gory and messy, well, yes it was," he said.

But he did not believe the research was cruel, as the animals were anaesthetised and did not regain consciousness before they were shot.

University animal ethics boards approved the research but are overseen by the national committee which is attached to the Ministry for Primary Industries.

Johnson said research is approved with the "three Rs" in mind: reduction of animals where possible, replacement of animals where possible and refinement of humane treatment to animals where possible.

The committee also has to be assured the outcome is worth the ethical cost to animals involved.

In the case of this study, Johnson believed the information gained was worth the cost of animal life.

"It's very difficult to provide a benchmark for what it means ... that's not a mathematical exercise, it's an ethical and philosophical exercise so you can't pin that down."

But he said the data set derived from the study means models can now be used for research, which gave it validity.

Another major criticism levelled by Kriek was the lack of transparency about research being approved, saying in the case of this research the public weren't informed until six years after the fact.

"If the research is so important for the country and economy … then why not be open and completely transparent?" he said.

"It's the ethics committee that should have the control, they should say prove how this is going to help humanity.

But Johnson pointed to processes in place for public interest to be represented, with a veterinarian practitioner, a local animal welfare group appointee and a local government authority appointee all on the committee.

This core group of members cannot be outvote and essentially have veto power.

"The intention of research is to put that information in the public domain," Johnson said.

"The ethics committee has obligations to the animals to approve research in a responsible way but there's also a responsibility to the privacy of people doing research in a private and professional sense."

Pigs were shot to simulate blood spatter patterns from gunshot wounds to human heads.