Last week, the board announced changes to movement control areas in North Canterbury, Marlborough and Wellington, following a national fall in infected herds for the 15th consecutive year.
But the Animal Health Board's (AHB) technical manager Paul Livingstone said, while infection rates were stable in the South, the board was waiting for more information.
It required evidence that relaxing boundaries would not result in a sudden increase in infection rates.
"We need some degree of certainty that any reduction is relatively permanent," he said.
Success in the board's vector control programme means 2045 farms across New Zealand will no longer need to test for Tb and a further 1500 no longer need to test animals before moving them off the farm.
While progress was being made in controlling vectors, Dr Livingstone said the task would become harder.
The residual ares of infected vectors were in rugged areas, often bordering bush and scrub which harboured pests.
Future gains in pest control would be more costly, as a result.
"While there is much good news to shout about, farmers and the AHB must remain vigilant. History has taught us some valuable lessons, particularly when you consider Tb infection rates peaked at more than 1700 in the early 1990s."
There are 120 infected herds nationally, 17% fewer than this time last year.
"The good thing is that we are not getting any regression in areas where we've made reductions," he said.