The first year results from a three-year research project on the economic and animal welfare impacts of docking lambs' tails have been inconclusive.
The Alliance meat co-operative is continuing the study, to see if trimming lambs' tails or leaving them intact makes any difference to their production and the risk of fly-strike.
The common practice on New Zealand farms is to remove lambs' tails, to reduce the build up of dags on the rear end of sheep and make them less vulnerable to fly-strike.
The research includes a farmer survey and field trials assessing four different tail lengths.
British supermarket group Sainsbury's is supporting the research
Alliance livestock manager Murray Behrent says British lamb buyers in particular have been critical of New Zealand tail docking practices.
"When the UK retailers come over, it doesn't matter which retailer it is, they all comment that they believe New Zealand dock their lambs too short, too close to the top of the tail," he says.
Mr Behrent says there is an animal welfare code that says tails must be docked at a certain length.
"That's also part of it as well, to make sure that New Zealand farmers dock at the right tail length at tailing time."
He says the researchers believe long tails create more dags, but that will be seen over the next few years.