One of two men who bashed a kangaroo to death with a metal pole has been jailed for almost a year, which is almost unheard of in Western Australia.

Craig Jamie House and Vance Geoffrey Jarvis both pleaded guilty in the Bunbury Magistrates Court to the ill-treatment of an animal.

The court heard police came across home video footage of the incident, which happened east of Bunbury in June 2015, on a computer seized during a raid on an unrelated matter.

WARNING: This story contains footage some readers may find disturbing.

The footage showed the pair cornering a kangaroo into a dam, throwing rocks at it and bashing it with crowbars until it became lifeless, before dragging it out of the water.

House was also heard instructing his dog to help corner the kangaroo.

Magistrate Evan Shackleton found House to be the instigator of the incident, delivering the first blow to the kangaroo and instructing Jarvis to join in.

"Sneak out to it man, as soon as it lunges 'boosh', take ya thongs off," House can be heard yelling to Jarvis.

House is also heard praising his dog named Dasher and 'Go, Dash dog' to the camera at the end of the video.

Kangaroo killed 'for meat'

The two men represented themselves at their Tuesday court appearance which was set down for a trial but both changed their pleas to guilty.

House told the court he killed the kangaroo to eat it because he was living off the land and was having a tough time financially.

He said his gun licence had been confiscated two years earlier and he did not want to purchase a gun illegally so used the crowbar as a weapon instead.

"I tried to put out the 'roo in the most humanely way I could," House told the court.

Sorry, this video has expired Men sentenced for brutal roo death ( Supplied )

Magistrate Shackleton disagreed and said there was a large element of cruelty by throwing rocks, egging on the dog and hitting the kangaroo in the head.

"For a number of minutes, you were not behaving humanely to that kangaroo," Magistrate Shackleton said.

"In my view, you were having fun tormenting that kangaroo."

Co-offender Jarvis said he had no idea the incident was being filmed and he only joined in to "put it out of its misery".

Police prosecutor Brian McCormack accepted that was "ultimately probably the case" and said Jarvis showed no celebration or jubilation at the end like House did, but that he had still been part of the chase.

Magistrate Shackleton said he was willing to accept Jarvis wanted to put the animal out of its misery but said he had not acted humanely.

"I lobbed rocks to try to get the kangaroo out of the water, I accept that probably wasn't humane," Jarvis said.

House was handed an immediate jail sentence of 11 months while Jarvis was ordered to pay a $10,000 fine.

First jail sentence in WA

RSPCA WA chief executive David van Ooran said it was the first known jail sentence handed down for animal cruelty in WA.

"It's incredibly rare — I can't think of a time in recent years and decades where this has occurred," Mr van Ooran said.

"This is a very strong penalty and a very appropriate penalty ... it was clearly a horrific and sickening act against a defenceless animal, behaviour like this is completely unacceptable.

"It's excellent to see that the magistrate in this case has awarded a prison term."

Mr van Ooran said he hoped the case would set a strong precedent for future cases.

He said the RSPCA was finding the prevalence of smart phone footage was leading to increasingly available evidence to prosecute animal cruelty cases, and they were receiving up to 50 reports per day.