The tricky balance is about to be tested in a very unusual way, as an upper house MP has been interviewed by police in relation to possible criminal offences over an incident where he used a drone to film over the piggery at Corowa. 

Mark Pearson MLC from the Animal Justice Party said he organised a drone pilot to join him at the site of the southern hemisphere's biggest piggery and abattoir in December 2015.

The footage that resulted did not show any animal cruelty, and Mr Pearson is adamant he did not break any laws that day.

He was contacted recently by a detective from Albury Local Area Command to be interviewed about offences relating to the Crimes (Domestic and Personal Violence) Act and the Surveillance Devices Act over the 2015 incident.

Two policemen formally interviewed Mr Pearson on Friday afternoon, but he was not arrested and it was not clear what, if any, charges would be laid over the incident.  

Mr Pearson has a history of animal activism and said he has been arrested and charged several times before under trespass or surveillance laws for filming the alleged mistreatment of animals, but never convicted. 

"I'm vegetarian. I'll be looking forward to the day when we don't rely so much on killing animals for food, obviously, but my main issue is how these animals are being killed." 

Video from the 2015 event which is posted online shows Mr Pearson declared himself as an upper house MP from the Animal Justice Party and formally sought permission to inspect the Corowa property.

He was refused and later had a pilot fly a small drone to film over the property, Rivalea.   

Rivalea is a piggery and also an abattoir where 1600 pigs a day are killed by being lowered in machinery into a carbon dioxide gas mixture before they are butchered. The gassing process is supposed to stun the animals so they are unconscious when they die. 

Mr Pearson said he was following up an incident in 2014 where two animal activists allegedly broke into the Rivalea abattoir and installed secret cameras which filmed pigs apparently in distress as they were gassed.

Mr Pearson later obtained the hidden camera footage and asked the police and an animal welfare expert, Professor Donald Broom from the University of Cambridge, to review it. Professor Broom reported the footage showed the pigs were extremely distressed, and were taking between 20 and 40 seconds to suffocate slowly rather than being knocked out quickly. 

No animal cruelty prosecution resulted, but the activists involved were charged with criminal offences in an ongoing case.  

At the time, Mick Hewat, the managing director of Rivalea, said "we were distressed and shocked to see the footage. This is not acceptable behaviour on any of Rivalea's properties. We expect high levels of behaviour regarding animal welfare from all of our employees." He said two employees were dismissed as a result of the incident. 

"Rivalea maintains a very strong commitment to animal welfare."

Contacted by Fairfax Media, Mr Hewat said they had made a police report at the time of Mr Pearson's visit but it would not be appropriate to comment further as it was a police matter. 

Mr Pearson defended animal activists who commit illegal actions such as trespass to expose animal cruelty, arguing that illegal practices in the intensive livestock industry can only exist where they are hidden from public view, but acknowledged that the police have to strike a balance.  

"The police are in a very difficult position because they've been asked to prosecute cases of extreme cruelty to animals and at the same time there's pressure on them to investigate and prosecute the same people who've taken the vision [that exposes the abuse]", he said.

The secret filming by activists of animal mistreatment has had big public impact in the past few years, famously almost shutting down the live export industry and greyhound racing. 

Mr Pearson is the first ever Animal Justice Party MP, elected to the 21st spot in the Legislative Council in 2015, on the back of strong preferences from the Greens.