Stuff.co.nz reports that about 50 chicken carcasses were found at the rural Martinborough property in January after council inspectors were tipped off by a neighbour.

The few surviving birds were found living without supplied food, in manure more than half a metre deep, and were engaged in cannibalism, according to a neighbour.

The SPCA visited the farm last August, then again last month as part of its investigation.

National inspectorate support manager Alan Wilson said officers had spoken to the owner, Wellington man Stephen Gunson, but had no choice but to close the case.

"The conclusion we've had to come up with is that there isn't enough evidence to prosecute.

"Prosecution has quite a high threshold ... and sometimes the evidence just doesn't meet that threshold."

Mr Wilson said possible issues of desertion, failure to provide sufficient food, and ill-treatment of the birds had all been investigated, but none could be proven.

The SPCA had not issued a warning but had spoken to Mr Gunson to "educate" him, Mr Wilson said.

In February, a neighbour told The Dominion Post that, at its peak, the farm held about 1000 birds and produced 900 to 1000 eggs a day.

The neighbour said many of the chickens had been culled before the property was abandoned last winter, but 200 to 300 birds had been left to fend for themselves.

Most of those had been killed by predators, died of exposure or been run over.

South Wairarapa District Council planning and environment manager Glenn Bunny said it was up to the SPCA to decide whether to prosecute.

"But [for them] to cite a lack of evidence, my only comment on that would be that they haven't interviewed myself or any of the other staff here since we reported that incident to them, so you can draw your own conclusions from that."

Wairarapa SPCA president Val Ball, who visited the property last year, described it as a "shambles" but said there was no way to prove the chickens' cause of death.

The 7.7-hectare property in Hinakura Rd is now on the market. Mr Gunson could not be reached for comment yesterday.