A small number of animals have been euthanised voluntarily by the farmer for animal welfare reasons.
Owner Aad Van Leeuwen told Fairfax he had wanted to kill the animals as soon as they were diagnosed, but had been advised not to as it was in the interests of the industry to contain the disease.
"It's devastating, especially for the people working on the farm. It just hits you and you don't know what to think, you don't know where it comes from," he said.
MPI's regional controller Dr Chris Rodwell says the situation is well under control.
"At this time we are still determining the scale of this situation through on- farm sampling and testing, and tracing of movements of stock on and off the properties.
"This will help inform our future management activities which we are currently working up in partnership with the animal industry bodies."
He says measures could include selective culling of some stock.
"We know other farmers in the area have concerns. This is entirely understandable. That's why we talked to a well-attended meeting of local farmers in Glenavy this morning.
"I'd like to assure people that the disease is a slow-moving one that is transmitted by close contact between animals and not across big distances by wind or water."
Mycoplasma bovis can be present in milk and transmitted to other cows this way.
"We need to be clear, though, that the presence of the bacteria does not affect the safety of dairy products for human consumption. This is not a food safety or human health concern."
What is mycoplasma bovis?
* A bacterial disease in cattle
* It can cause udder infection, abortion, pneumonia and arthritis
* Commonly found in cattle globally, including in Australia. - NZN
