Keith Woodford explains why European semen is the likely source of the disease, and how this helps explain the rapid spread

By Keith Woodford*

It is now increasingly evident that European-sourced semen, imported legally but containing live Mycoplasma bovis that survived the antibiotic cocktail, is the likely source of the organism in New Zealand dairy.

The evidence suggests it struck first in Southland, but there is a likelihood is that the same semen has struck on other farms, and then spread from there via progeny.

It is also likely that Mycoplasma bovis arrived in New Zealand via this semen by late 2014 or even earlier.  This is an important issue because so far MPI has only focused on events since the end of 2015.

If the above statements about semen and time of entry are correct, then there are profound implications for the eradication program. In effect, we could be fighting six or more fires from the different strikes and possibly more that have yet to be identified.

The above explanation is also the likely reason why the spread of the infection has been much faster than MPI and its advisers expected. The stealth bomber dropped its load in multiple places.

The reason that I believe semen is now the most likely source of the disease is that no other single source can explain the range of infected properties.  I have been puzzled for many weeks by MPI’s somewhat soothing claims about farm linkage, which did not fit with the evidence famers were telling me.

What I found was that three infected Canterbury farms that lacked obvious live animal links to either the Van Leeuwens or Zeestratens, plus the Van Leeuwens and the Zeestratens themselves, were all using the same source of Northern European semen. This does not constitute proof, but it does provide a pointer.

The official position of MPI to date has been that there has been only one outbreak. Initially, MPI said that it started in South Canterbury and that it was confident the outbreak started in 2017. I have seen official correspondence from MPI stating that MPI was only interested in animal movements for 2017. Eventually they had to concede that it arrived in Southland well prior to this, most likely by their current calculations at the end of 2015 or early 2016.

MPI has not publicly stated how it thinks the organism entered New Zealand, but the inference is apparent from other actions. Quite clearly, MPI has recently been of the perspective that it was likely to have been through infected veterinary drugs, perhaps imported illegally. That source is still a possibility, but there are increasing challenges to that likelihood, including that it does not explain the rapid spread.

MPI’s focus on veterinary drugs was highlighted by its warranted raids on three properties, including a veterinary clinic based on Waiheke Island. Also, within the MPI Pathways Report as to how Mycoplasma bovis might have got to New Zealand, all reference to veterinary drugs, including even the inclusion of the category, was redacted prior to release of the report. For those who could identify the missing category, that redaction highlighted where MPI’s detective focus lay.

A key piece of evidence as to how the disease might have got to New Zealand is the genetic tracing.

So far, the New Zealand variant of Mycoplasma bovis is unique within the international Mycoplasma bovis database. However, it is only one locus (mutation) away from an apparently old European variant, with this variant having also been identified, but less common, in the United States.

Mycoplasma bovis genetic variant map; NZ variant dark green with red outer circle. Source MPI Paper 2017/1

The synthesis of information from within the genetic map suggests that it probably came from one specific source in Europe.  That does not preclude the possibility that variants of Mycoplasma bovis have been here for a long time. But it does indicate that all of the limited samples tested so far have likely come from one European source. Also note that I said this comes from the limited samples tested for genetic variation. There are lots of uncertainties.

If I am correct, and semen is the source, then no farmer is to blame for the arrival of the disease. Also, the likelihood is that no importer of semen has broken the law. Rather, the laws around importation of frozen semen and also embryos were not strict enough. 

The law did not require donor bulls to be tested. All that was required was that no Mycoplasma bovis had been found. But if you don’t look, then you can truthfully say you have no evidence of it being present.

Alternatively, if the infection has come through imported veterinary drugs, then things get somewhat murkier. But even then, unless the drugs were imported illegally, or used for an illegal purpose, then the farmers concerned are not to blame. Once again, the rules have been that you cannot import drugs known to come from an infected source, but there was no requirement to test.

This situation of not having to test arises from the fact that Mycoplasma bovis has always been regarded internationally as a minor disease. Also, whereas Mycoplasma bovis can hide from antibiotics when it is inside the animal – what is called ‘in vivo’ – it is more susceptible to the antibiotic drugs when present within semen or drugs. So, the usual response has been to treat the semen with antibiotics and then hope.

It is already known that Mycoplasma bovis genetic material has been found in imported frozen semen used by infected properties. This is stated in MPI’s Pathway Report. However, so far it has not been possible to culture this in the test tube, suggesting it has all been killed by the antibiotics. But it would only have taken one faulty batch for it to have slipped through.

Back in 2017, it was possible for MPI to say that there were no documented cases of Mycoplasma bovis being transmitted anywhere in the world through frozen semen. However, that is no longer the case, with a documented transfer in Finland reported in a paper within the Journal of Veterinary Microbiology. This paper has been circulated within some New Zealand veterinary and agricultural science groups, but it has not been acknowledged by MPI.

So far, New Zealand appears to be the only dairy-producing country to have raised the status of Mycoplasma bovis to that of a major disease. We may have been right to do this, but to date the rest of the world has not followed.  Rather, in all these other countries farmers manage the disease themselves. There have been some nasty outbreaks, but nearly all farmers have it under control as just a minor nuisance with appropriate management.

With hindsight, it is obvious that there was a contradiction between on one hand our New Zealand attitude that Mycoplasma bovis is important and on the other hand the biosecurity processes that we had in place. Our biosecurity arrangements were those of a country, like elsewhere in the world, who thought that the disease was just a nuisance that could be lived with.

There still remain other possibilities as to how Mycoplasma bovis got to New Zealand. For example, live animals are an obvious risk but there have been no animals imported since 2013. Prior to that there were imports from Australia, but the current evidence is that the New Zealand variant of the disease did not come from Australia – it has the wrong genetics for an obvious Australian source.

There is also the prospect that it came in via embryos. Over the last ten years there have been more than 5000 embryos imported to New Zealand. Most of these embryos probably went to the companies that sell semen. They would have used these embryos to produce new genetic material for their bull mating teams. There has been very little discussion about this as a potential source, including as a mechanism for Mycoplasma bovis getting into the semen.

Trying to see through the murk of MPI to get solid information is extremely difficult. Those of us who have a science background have found it impossible to date to get access to people with whom we can have an intelligent science-based conversation. The presentations to industry have been very superficial.

MPI points out repeatedly that it is advised by a Technical Advisory Group (TAG). MPI has recently provided the names of the 11 people in the group. Eight of them live overseas. I have tried to contact the NZ-based chair of the group but this person is also currently overseas on other business.

There are only two reports from the TAG that I can find. One was from a meeting in November 2017 and the latter was the report from a telephone hook-up in February 2018.  It seems that this group is very much part time and is called in sporadically. And they are themselves dependent on information provided by MPI. In their first report, they were politely but firmly critical of the quality of the information they were receiving.

It is clear that MPI does indeed have some specialist expertise within its team.  For example, the anonymous and redacted MPI Pathways Report was clearly written by someone who has lots of relevant expertise in terms of disease pathways. But that person is also operating from limited data.

MPI has currently advised the media that the reason it thinks Mycoplasma bovis has only been here for a maximum of two years is because of the genetic tracing and genetic time-clock. I have to question that judgement and I would love to hear the precise words of the scientist who supposedly made that call.  I know a little about genetic time-clocks and I suspect that there would have been all sorts of caveats that the scientist placed on that.

The key element of a genetic time-clock is the rate of mutations. We know that Mycoplasma bovis has great ability to evolve, but there is also evidence that this rate varies considerably in different environments.

One of the messages from the suspected botulism outbreak some five years ago was that scientific information, once transferred through multiple levels of non-scientist management, in that case within Fonterra, gets highly distorted. We need to be confident the same thing is not happening here.  The recent report on methamphetamine contamination here in New Zealand also illustrates what happens when non-scientists make an ‘inexplicable leap of logic’ (to quote Chief Government scientist Sir Peter Gluckman).

The question has to be asked as to why MPI is being so precious with the information they have at hand?

One suggestion I am getting is that MPI at senior levels has a culture of telling farmers no more than what is necessary, and MPI considers itself the arbiter of what farmers need to know. Or it could be, that with no science-trained biosecurity experts in their ten-person leadership team, and similarly at the next level of program management, that messages are getting muddled and omitted as they work their way through the chain. The third reason is that MPI lacks nimbleness. Like many bureaucracies, as the evidence changes, the non-scientist leaders struggle to stop defending a position and move quickly to solid ground.

It may also be that MPI is trying to protect its ability to take a court case against illegal actions. That is the only conclusion that can explain the ridiculous redaction of even mentioning ‘veterinary drugs’ as a potential category.

The problem for farm businesses – and there are well over 10,000 of these that are in risk management mode – is that it is impossible to put together sound plans without transparency of information.

In minimising risk, farmers have to make judgements as to where the greatest risks lie and act accordingly. Getting these assessments right is going to be crucial to the potential overall success of any national eradication program. Farmers and Government are in this together; it is not just Government.

In the current situation, there is a need for all of the semen companies to come forward and explain the measures that they are now taking for the coming season. Indeed, right now there are farmers using semen for next year’s autumn calving.

We need to know for each of those semen companies as to the measures they now have in place to minimise risk from their semen. This is not just for imported frozen semen, but also for fresh local semen where there are historical links back to imported embryos or semen, or where the bulls have been in contact with other bulls that have such a background. In fact, with the extent of the current outbreak, it needs to be for all of their bulls.

Although the Pathways Report from November 2017 suggests possible measures that can reduce the risks from semen, these are not yet legal requirements. So, all semen companies need to front up and tell us precisely what they are doing. I know that some companies have already changed their practices, but I do not know for all companies. The notion of ‘trust us’ is not good enough.

My own judgement right now is that the greatest risk to dairy farmers is from what are known as ‘service bulls’ which are used as follow up after two or three cycles of artificial insemination. Particularly risky is any bull that contains European-sourced genetics or which has been in contact in any way with such an animal. For graziers who run dairy support blocks, the greatest risk is that the calves coming onto their property will be infected.  Where female calves from different farms are run together by these graziers (as is common, particularly in the North Island), then there is a risk of subsequently transferring the organism back to all of the home farms.

*Keith Woodford was Professor of Farm Management and Agribusiness at Lincoln University for 15 years through to 2015. He is now Principal Consultant at AgriFood Systems Ltd.   His articles are archived at http://keithwoodford.wordpress.com. You can contact him directly here.