The confirmation of Mycoplasma bovis on two Ashburton properties this week, with a third under investigation, wasn't a surprise, says the Ministry for Primary Industries.
MPI picked up the properties through its background Bulk Tank Milk (BTM) surveillance programme, that is run though all dairy herds around New Zealand.
It had been expecting to detect the cattle disease during spring more than at other times of the year, due to the stress of calving, director for the Mycoplasma bovis programme, Stuart Anderson said.
"This is the time of year with heightened stress, if there's M.bovis out there in animals, we are more likely to find it" Anderson told The Country's Rowena Duncum.
It was understandable that the return of M.bovis would cause "some nervousness" in Ashburton, but people shouldn't worry, he said.