Keith Woodford says we should not be confident we have the Mycoplasma bovis contained, particularly since we still have no idea as to how the disease got here

By Keith Woodford*

For most New Zealand dairy farmers, the Mycoplasma bovis outbreak in South Canterbury is now little more than background noise.  However, dairy and even beef farmers would be wise to recognise that it could still be lurking anywhere in New Zealand, waiting for the right circumstances to strike.

The whole saga of the outbreak has been poorly communicated.

The starting point for error has been the widely reported falsehood that it is on intensive confinement farms owned by the van Leeuwen Group.   In fact, the disease has not been detected to date on any of the four robot-milked free-stall farms owned by this family. Rather it is on five outdoor farms that they own.

One of the infected farms does have indoor wintering facilities. That farm is on heavy land with two free-stall barns available for wintering and in bad weather. But this is not an intensive farm like in America or much of Europe. These are grazing cows. And the intensity is broadly similar to some hundreds of New Zealand farmers who have off-paddock wintering facilities of various types.   Unlike many New Zealand farms, this farm does milk cows during the winter.

Two of the other infected VLG farms have spring calving and seasonal milking. Another is a dry-stock farm, and the remaining infected farm is a calf-rearing unit.

The media has widely portrayed the van Leeuwen family as so-called rich listers. What has not been portrayed is that this family has got there the hard way. Aad immigrated to New Zealand in 1983, and Wilma’s parents also immigrated from Holland. Aad and Wilma worked their way up the dairy ladder, first as farm workers, then as managers, contract milkers and sharemilkers, and finally as farm owners.

It has been a more than thirty-year journey of hard work, innovation and business acumen. Some of their children are also now involved in the business. 

I have taken an interest in the outbreak since first detected back in July. I contacted the van Leeuwens at that time to try and understand what was happening, and I have stayed in touch. My interest is that of a semi-retired academic who likes to follow issues from an independent perspective. I go wherever the evidence takes me.

Back in August, I wrote an article on  Mycoplasma published here at interest.co.nz and elsewhere.  At that time, I wrote that “Regardless of whether or not the current outbreak can be contained, and the disease then eradicated, the ongoing risks from Mycoplasma bovis are going to have a big effect on the New Zealand dairy industry”.

I also wrote back then that “If the disease is contained and eradicated, then the industry and governmental authorities will need to work out better systems to prevent re-entry from overseas. And if the disease is not eradicated, then every farmer will have to implement new on-farm management strategies to minimise the effects.”

Those statements remain unchanged some three months later.

Early on, it was widely stated that imported semen was the most likely source. Even Bill English, who was Prime Minster at that time, stated that semen was the likely source.   Most likely this was on advice from MPI. However, MPI have subsequently downplayed strongly the likelihood of semen as the source. It is just one possibility.

My understanding is that there has never been a documented case anywhere in the world of it being transferred in frozen semen, and all imported semen is frozen.

Aad van Leeuwen tells me that the van Leeuwen group has never imported semen themselves. However, like many other farmers, they do purchase semen from the major semen companies. If semen is the source, and the disease is not elsewhere, then the van Leeuwens have been exceedingly unlucky to be the only farmers to be struck. And if that is the case, then a great many other farmers can only thank their lucky stars that it was not them.

Given the lack of evidence for semen being the source, other possibilities need to be considered.

The normal transmission method for Mycoplasma bovis is from animal to animal. That raises the possibility that the original source is a live import. However, the oral advice from MPI (yet to be confirmed in writing) is that there have been no live cattle imported into New Zealand for the last three years.  

Regardless of when animals were last imported into New Zealand, the importer was not the van Leeuwens, and the van Leeuwens have never received live imports on their farms. So once again, if a live import is the source, then the van Leeuwens have been exceedingly unlucky to the recipients of the disease. And what was the path by which it got there?

Molecular biologists may eventually be able to identify the strain of the organism and thereby identify its source as either Australian, which could implicate a live import, or alternatively Europe or the USA, which could implicate semen.

Testing for Mycoplasma bovis is not easy. Testing of individual animals can be by antibody (ELISA) testing of blood, but there are problems of both false positives and false negatives. Bulk tests of milk can be made using sophisticated PCR (polymerase chain reaction) technology that seeks out key DNA sequences, but this will only give positive results if the animals are shedding the bacteria in their milk. With PCR, and with the levels of specificity being used, it needs multiple animals to be shedding before a positive reading is achieved. Swabs of animals can also be taken and tested.

In regard to testing, the bottom line is that no method is reliable by itself and multiple tests are required. The van Leeuwens have experienced this themselves, with one of their herds testing negative on two occasions and only on the third test did a mass of reactors show up. In the periods between the tests, no new animals came onto that farm, so presumably it was there all along from prior to the first testing.

There is now good confidence that all animal movements downstream from the van Leeuwen farms have been traced, and those herds continue to be rigorously tested. However, it is far from clear as to the extent of any upstream testing looking for the original source and dissemination from there.

The VLG-owned herds have been closed herds with no new animals brought in from outside the group for more than three years. However, like probably the majority of New Zealand farms, one sharemilker-owned herd on a VLG property has had animals brought in, and this herd is infected.  This raises the possibility that it first came onto the van Leeuwen farms up to several years ago, but only became evident when it spread into one of the milking herds.

MPI have not been forthcoming as to the upstream (source) testing that has been conducted. But Aad van Leeuwen tells me it is his understanding that MPI upstream testing has not been undertaken looking at source farms going back prior to the start of the 2017 year. If this is correct, then it would seem an important omission.

Although MPI have conducted many thousands of tests, it is not clear as to the proportion of New Zealand’s farms that have undergone any testing, and the level of that testing. Almost certainly, it is only a small proportion of farms that have been tested. MPI have been unable to provide this information to me. And therein lies the uncertainty.

One of the problems we have in New Zealand is that the only Kiwis with Mycoplasma bovis expertise are those who have worked and trained overseas.  I know the van Leeuwens are drawing on overseas expertise, but it is not clear to me as to the extent MPI is benefitting from overseas expertise.

What I am personally hearing from people with overseas Mycoplasma bovis experience is that we should not be confident that we have the disease contained. This is particularly the case given that we really have no idea as to how the disease got here. 

If Mycoplasma is found to be endemic in New Zealand, then it will not be the death knell of the industry. But it will be a big nuisance. And we will undoubtedly need to implement some of the dairy hygiene measures that are typically seen overseas but which are largely ignored in New Zealand. In particular, farmers will need to think carefully about sending their young stock off-farm for grazing with young stock from other farms. Feeding raw (non-pasteurised) milk to calves will also need to be eliminated.   Purchased bulls are another potential source of disease transfer.

*Keith Woodford is an independent consultant who holds honorary positions as Professor of Agri-Food Systems at Lincoln University and Senior Research Fellow at the Contemporary China Research Centre at Victoria University.  His articles are archived at http://keithwoodford.wordpress.com. You can contact him directly here.