There were some seriously worried people at Federated Farmers' seminar on the cattle disease M. bovis on Monday.

One couple grazes weaner dairy cattle on their farm, usually hosting young cattle from six different farms. How could they be sure the cattle didn't bring the disease?

The upstairs rooms at Wanganui Veterinary Services were packed with about 200 people for the seminar.

New Wanganui Federated Farmers president Mike Cranstone said the meeting was not to talk about the rights and wrongs of the disease eradication programme, or to lay blame.

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He brought the large crowd to attention with a loud dog whistle.

Beef + Lamb NZ speaker Paul McCauley has been working in Southland, which has 95 per cent of the disease. He began with some words of reassurance.

Paul McCauley tells Whanganui farmers about the cattle disease M. bovis. Photo / Stuart Munro Wanganui Chronicle
Paul McCauley tells Whanganui farmers about the cattle disease M. bovis. Photo / Stuart Munro Wanganui Chronicle

"The main thing I want you to take away from this is to keep calm and carry on farming. You will just have to keep your own businesses safe and secure - it's not complicated or expensive."

By far the most likely way for M. bovis to move to a new property is by the introduction of infected cattle (75 per cent). Calves drinking infected milk are also 80 to 90 per cent likely to be infected.

Nose to nose cattle contact and infected boots and equipment are much less likely ways for the disease to arrive.

"It's not highly contagious. It's actually quite hard to spread," vet John Pickering said.

Less than 10 per cent of the neighbours to the Van Leeuwen farms in South Canterbury, where M. bovis was first diagnosed, have the disease.

Nonetheless farmers are being told to avoid their cattle having nose to nose contact with neighbouring cattle, and to disinfect the boots and equipment of visitors. It takes two hours to disinfect trucks carrying infected cattle, and transport operators are expected to do this.

The cattle disease mycoplasma bovis was confirmed in New Zealand in July last year. There are now 36 infected properties, with one in the Manawatu and near Pahiatua, according to the Ministry of Primary Industries website. Another 1700 properties are being watched, and 130 of those have movements of stock and materials restricted.

So far all the cattle moved from infected farms have been traced, and nearly 24,500 have been killed. Their owners are being compensated.

The full eradication campaign will cost an estimated $886 million, with Government paying 68 per cent and a $16 million cost to business.

M. bovis is present in most countries with cattle, McCauley said. The bacteria can't be controlled by vaccine or antibiotic. The disease only affects cattle, so that milk and meat from infected animals is safe for humans to consume.

It's a tricky disease, because an animal can be infected and can spread it, without showing any signs. There are two tests for it, but they can throw up false negatives and false positives.

"It's very, very rare to get a 100 per cent guaranteed answer on anything," McCauley said.

Infected cattle will only show signs of having the disease when they are under stress. Signs include lameness, swollen joints, mastitis, late abortions and pneumonia.

Only one strain of the disease has been found so far, which means it probably has a single source. DairyNZ speaker Rob Brazendale said that source is being actively investigated, to prevent the disease arriving again.

Anyone who suspects their cattle has the disease should ring 0800 99 66. To get on a mailing list for updates, email Mbovis2017_liaison@mpi.govt.nz.