In a fiery debate in NSW parliament on Thursday afternoon, members of the lower house voted down recognising a petition to repeal the bill giving wild horses in Kosciuszko heritage status.

During the heated proceedings, NSW Deputy Premier John Barilaro began to yell at the members in the public gallery before one of them gave him the middle finger.

It also saw Mr Barilaro at odds with the state environment minister Matt Kean, who said it was important to listen to the science.

The public gallery later shouted "shame" at MPs after the petition was voted down. During a division on the vote, the chamber's microphone picked up a male MP saying "who cares, it's bullshit".

Labor MP Trish Doyle said the Brumby Bill was the "personal project" of Peter Cochran, who runs a Brumby tour business in the Monaro.

Mr Cochran, a former Nationals member, is Mr Barilaro's predecessor in the electorate.

"[Mr Cochran] has monetised horse treks through the national park," Ms Doyle said.

"That is what this is actually about."

"We must not allow this parliament to be used to advance the personal profits and self interest of a former member."

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Mr Cochran had previously made a $5000 donation to Mr Barilaro's election campaign in the lead up to the 2011 state election, but hasn't made any since.

When contacted by The Canberra Times, Mr Cochran said it was "gutless politics" to use parliamentary privilege to attack people.

"I will put my character and integrity up against anybody in this country," Mr Cochran said.

"I knew two years ago, before this issue came into parliament, that there was a fair chance that my business would be closed down as a result of the Snowy 2.0 project."

During the debate, Mr Barilaro accused Ms Doyle of using parliament and parliamentary privilege to slur Mr Cochran.

He said a "group from inner city Sydney" was trying to tell people in the mountains and NSW's regional areas how to live.

"Don't disrespect the people of the Monaro," Mr Barilaro said.

At one point, he turned to the public seated in the chamber and began yelling where a member of the public gave him the middle finger.

"That's disrespectful," Mr Barilaro said.

The Kosciuszko Wild Horse Heritage Act gave heritage protections to feral horses in the national park, favouring non-lethal methods to control their numbers.

With a population estimated to be close to the tens of thousands, environmentalists are concerned the horses are damaging native ecoystems in the park. This included habitats for the critically endangered northern corroboree frog.

The ACT government is concerned if the horses are left unchecked, an established population across the border would destroy the capital's water supply, as well as native flora and fauna.

Mr Barilaro told the chamber aerial culling was not humane. The most recently drafted management plan, which was thrown out after the "Brumby Bill" was passed, only suggested ground culling to control numbers.

State environment minister Matt Kean said one of the biggest threats to NSW's national parks was feral animals, including horses.

"I saw for myself first hand one of the most beautiful natural environments in the world and the devastating impact the number of feral horses are having on that environment," Mr Kean said.

"We need to return to the science when it comes to environmental policy."

He indicated a scientific committee, which would spearhead the new management plan required under the "Brumby Bill" would soon be appointed.

When a spokeswoman for Mr Kean was asked to clarify the timeline, she said it would be announced "shortly".