Ranginui's friend held the sheep down while he knifed it and skinned it, before they took the meat home to be divided.
The farmer was left to clean up the "mess" left behind, the court heard.
However, Judge Phillips said the most serious offence was an assault which took place while Ranginui and a friend were drinking in a Balclutha bar in July.
While the pair were in the smoking area the defendant's associate engaged in a verbal spat with a man on the pavement.
The men chased the victim down the road where they eventually caught him.
"Then, you and your friend gave him a hiding, punched him over and you had to be separated by hotel staff and members of the public," the judge said.
"But you weren't done. You totally lost control of yourself. You continued to try and get to the victim.
"He was getting in a van, trying to get out of the area, and you punched him in the head then kicked out at the van."
The man suffered facial injuries, the court heard.
The attack was part of a pattern of aggressive outbursts, which began four days earlier.
Ranginui had been sitting outside the Salvation Army office on Clyde St when he began arguing with another man.
They eventually went outside to fight but made off before police arrived at the scene.
Ranginui later told them no punches had been thrown but last month pleaded guilty to fighting in public.
The judge was bewildered how such an incident could occur at the premises, "when the Salvation Army are there trying to help people".
The sheep was not the only theft Ranginui was sentenced for yesterday.
David McCaskill said his client's shoplifting of a speaker on two occasions was "run of the mill" but Judge Phillips, disagreed saying at least one of the incidents was planned with accomplices who distracted staff.
When police executed a search warrant at Ranginui's home they found both speakers - one defaced, the other "filthy".
Mr McCaskill urged the court to consider the defendant's rehabilitative needs.
"He's a young 20-year-old who's got quite a bit of maturing to do," he said.
"Prison's not really the best place for him, in that he's probably very easily adversely influenced by his associates."
But Judge Phillips said Ranginui's criminal history was "a major concern", along with his numerous breaches of home detention in the past.
As well as the jail term, he was ordered to pay $400 reparation to cover the farmer's losses.