A homeless man who bashed a ginger cat named Garfield to death with a large rock has been jailed for 10 months.

Judge David Saunders imposed the sentence on 44-year-old Adrian Paul Burton in the Christchurch District Court, after getting a psychological report showing there was no major mental illness.

Burton had admitted the charge of wilful ill-treatment of an animal, though he had considered defending the case because he believed the cat had been ill and he had euthanased it.

Burton has 11 pages of computer print-out listing his previous offending: mainly anti-social offending and breaches of community-based sentences.

This offence happened at 8.45am on August 11 when he was at an address in Poulson Street, Addington, where he stores some of his belongings.

He has lived there previously.

He saw Garfield, which also frequented address, and picked up the cat and placed it in a sack.

The police said: "He picked up a large rock. He then struck the bag repeatedly with the rock during which the cat was screaming loudly. He continued until the cat was silenced and the bag was covered in blood."

Defence counsel Vicki Walsh acknowledged the incident was "disturbing and abnormal".

Burton had a record of previous offending but nothing of this nature.

She said the incident happened at a time when he was homeless. He had not slept for several days, and had been under emotional stress.

Judge David Saunders said he had earlier ordered a psychiatric report because a letter from Burton had called his thinking into question. A later letter was more coherent.

"In cases of this kind, almost inevitably judges are berated up and down the country because they have been too lenient or haven't taken into account the maximum penalty provided under the act."

The maximum jail term is five years. Burton's actions had simply been "extreme violence to this defenceless animal", the judge said.