Thirteen days into the response to the outbreak, and MPI was "making very good progress". Indicating the scale of the task, the lab had processed about 1200 samples to date, he said.
At a public meeting in Papakaio earlier this week, frustration was evident among farmers as they awaited the test results.
Mr Gwyn said he realised farmers were keen to get answers as soon as possible.
"Our lab teams are working quickly and thoroughly, seven days a week, and we have increased staff numbers to carry out the work. On average, the process takes up to seven days from taking the sample on-farm to getting back to the farmer with the results."
MPI vets, scientists and on-the-ground staff were working hard on the response and getting "great support" from industry organisations. MPI remained focused on eradicating the disease from New Zealand, he said.
The disease has serious effects on cattle including mastitis, abortion, pneumonia and arthritis.
It was first isolated in the United States in 1961, in a bovine mastitis case, and since then, it appeared to have spread to many countries around the world, including most European and American countries, Massey University senior lecturer in anatomical pathology Dr Fernanda Castillo Alcala said.
It could cause serious and economically costly diseases. The economic consequences were reflected in terms of expenses associated with preventive and therapeutic medications, isolation of diseased animals, increased time on feed, increased labour, mortalities, poor productive performance and decreased carcass merit.
Animal welfare was also an important consideration, as the disease might progress to a chronic, debilitating condition that was unresponsive to treatment, she said.
Rapid diagnosis of Mycoplasma bovis infections was "fundamental" to the prevention and effective control of the disease.
Deciding what monitoring and control strategies to use in New Zealand would depend on the extent of the problem, she said.
MPI has advised farmers to look out for unusual mastitis in cattle that did not respond to treatment, arthritis in cows and calves, late-term abortion and pneumonia in calves.
Not all infected animals got sick but they could pass on the disease to other animals. Mycoplasma bovis spreads between animals through close contact.
The 16 Van Leeuwen Dairy group farms were under MPI movement control through restricted place notices. Cattle could only move between the other farms in the enterprise and be transported direct to slaughter at agreed premises.
