A report into greyhound racing has made "disturbing" and "disappointing" findings, Racing Minister Winston Peters says.
It highlights serious welfare concerns, including 53 greyhounds who were euthanised within five days of their last track day because they were "unsuitable for rehoming".
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The report, completed by former High Court Judge Rodney Hansen QC, says there is no reason that should be happening.
"It is implausible that a dog can be judged unsuitable for rehoming and euthanised for that reason within a few days of its last race," the report says.
A total of 308 dogs "unsuitable for rehoming" were euthanised, the majority within the first month of their retirement, and a further 175 were killed with no reason given.
The average age of death for a racing greyhound was 3.6 years while for non-racing greyhounds it was just 18 months.
Of the 8891 dogs monitored, just 1123 made it past age five.
In the 2016-2017 year, 36 dogs died, while 270 were euthanised.
Over the last three seasons,165 greyhounds have died while racing or have sustained injuries of such severity as to require them to be put down.
The report found there's no information about what's happened to more than 1200 unaccounted for dogs.
It questions whether it's necessary for earbranding of greyhound puppies to continue, and says if it is, it should be done under local anaesthetic.
"When the welfare of greyhounds should be paramount, the Hansen report has revealed rates of dog euthanasia, the numbers of 'unaccounted' for dogs, and low numbers of rehomed greyhounds which are simply unacceptable," Mr Peters said.
"While the industry has taken steps to improve greyhound welfare it still has a long way to go to clean-up the sport. It is not tolerable having some owners giving the rest a bad name."
Mr Peters met with the NZ Racing Board this week after it received the report and said, "The industry was left in no doubt just what dismal view the government has of this."
The report recommended improvements on kennel inspections, dog tracking, an approvals regime before a dog can be euthanised, track safety, dog rehoming, and stricter enforcement of the dog health and welfare standards.
The NZ Racing Board commissioned the review and the findings and recommendations were released publicly on Wednesday morning.