Keith Woodford discusses outcomes and strategies for controlling Mycoplasma bovis

By Keith Woodford*

It now seems likely that Mycoplasma bovis is in New Zealand to stay. Just like the rest of the world, we must learn how to live with it. We do not yet have to give up totally on hopes of eradication, but eradication is looking more and more unlikely.

The control program has suffered from incorrect information and poor communication, and there is much to be learned from that. These information flaws have affected farmer and public attitudes. In some cases, this has created additional and unnecessary stress, and unfair criticism of individuals.

However, the probability is that these flaws have not affected the success or failure of the eradication program. The chances are that Mycoplasma bovis has been here for some years, in which case eradication was always going to be impossible.

The starting point for moving forward is for MPI (the Ministry of Primary Industries) to provide more transparency about the current situation. MPI has consistently stated that all infected farms have a link to the Van Leeuwen Group via animal movements, but that no longer stands up well to scrutiny. 

The problem may well be that admitting that evidential links do not exist between newly identified infected farms and the Van Leeuwen Group would be a clear admission that, in terms of eradication, the horse has bolted. And MPI is not yet quite ready for any such admission.

Aad Van Leeuwen tells me that he is totally baffled by the MPI claims that these links exist. And he has failed in his attempts to get MPI to define those links.

In the case of the infected Hawke's Bay farm, it is indeed correct that a previous Van Leeuwen sharemilker sold animals to that Hawke's Bay farm. But the Van Leeuwen sharemilker's herd that those animals came from (now owned by the Van Leeuwen group; i.e., no longer owned by the sharemilker) has been tested five times and has tested clean each time. It is no longer a restricted herd. 

So, the likelihood is that it has been the additional testing scrutiny that the Hawke's Bay farm has been put under (because of those animal movements) that has led to the positive findings, but that these animals were not actually the source. In that case, no one knows how it got to the Hawke's Bay herd. Without the particular scrutiny this farm was put under, the presence of the organism would probably have gone undetected.

In the case of the Southland infections on the Zeestraten farms, it is correct that the Van Leeuwens and the Zeestratens know each other.  But there is no evidence of animal movements between the two groups of farms.

It is also increasingly unlikely that there are direct links between the Van Leeuwens and some of the other South Canterbury infected properties. One such property is close to a Van Leeuwen farm but is separated by a road and a 20-metre flood channel. And in any case, that particular Van Leeuwen property has also been tested multiple times and been declared free of infection.

There is yet another South Canterbury property that has tested positive but MPI has given no publicity to that fact. Rather, they have advised Aad Van Leeuwen (I have seen the correspondence) that “we are generally not reporting new detections unless there is something of significance or public interest”.

I think most farmers would like to be informed about another farm being found positive rather than having to rely on MPI’s judgment as to whether having that knowledge was in their interests, or alternatively having to rely on the bush telegraph. And this particular farm is indeed linked to multiple other farms throughout New Zealand, although MPI says they think all links were prior to the risk period. But none of us actually know when the risk period started, because we don’t know when or how that farm was infected.

There are also other infected farms, such as the Ashburton farm, for which links to the Van Leeuwen group have not been defined.

It is now becoming increasingly likely that the Van Leeuwen farms were not the first to be infected. Rather, because of a particularly diligent veterinarian, they were the first to be identified. And that perspective changes everything in terms of the practicality of national eradication.

In previous articles [here and here], I have focused on live imports and semen as the most likely original source. But now I am giving increasing weight to the possibility that it may have come in from imported embryos. Regardless, the Van Leeuwens did not import live animals, semen or embryos. Accordingly, it was always hard to see how they could be the original source.

So, if Mycoplasma bovis is here to stay - and all of us surely still hope that it is not - then how do we manage it?

Once again there are no simple answers. I have been reading up on the available information that I can find in the international literature, but it is confusing, and not helped by the absence of simple reliable tests for the organism. This Mycoplama bovis is indeed a tricky little devil with great ability to hide.

For farmers, there are three key questions. The first is what should they do to minimise the chance of infection? The second is what are the signs that they may have Mycoplasma bovis? The third is what should they do if they do get an infection?

The answer to the first question is easy in theory but difficult in practice. It requires running closed herds without purchase of animals. It also means strict hygiene procedures are needed for farm service people who move between farms. Livestock trucks will need to be cleaned thoroughly between jobs involving inter-farm transfers. 

In practice, running totally closed herds is not an option for most farmers, but the other two sets of procedures are more practical. There will continue to be animal movements between farms and that will be the main way by which the disease spreads.

Our dairy systems have developed on the premise that all herds have good fundamental health status and that animals can be safely bought and sold. But the evidence for that has always been fragile. One only has to think of Johnes disease (pronounced Yo-knees), which is an infective disease endemic in many herds. 

Farmers will need to give a lot more thought about young stock being raised away from the home farm (as occurs currently on probably most farms) and also about off-farm wintering of cows (as is particularly common in the South Island).

The key first indicator of Mycoplasma bovis in lactating cows is likely to be mastitis in multiple quarters of the udder rather than a single quarter, combined with non-response to antibiotics. This may or may not be combined with arthritic joints. In many cases there will be no symptoms, but the animal will still be infected and may be capable of transmitting to other animals. Even when there are suspicious symptoms, it may not necessarily be Mycoplasma bovis.

In young stock, the first symptoms are likely to be respiratory issues and arthritis.

The question of what to do when an infection is found is vexing. Once symptoms are evident, then the outlook for full recovery is bleak. These animals should be quarantined immediately and, at least for lactating cows, then culled. But that is unlikely to result in a clean herd, because there may also be infected animals present that show no symptoms. Over time, antibody levels in the herd and hence disease resistance will probably increase, but calves will remain susceptible.

Ensuring all newborn calves receive good quality pasteurised colostrum rather than fresh from the mother cow will be important in any herd that does have Mycoplasma bovis.

The other key insight from literature is that the likelihood of an outbreak of Mycoplasma bovis symptoms is more likely when animals are under stress. This could be related to bad weather, insufficient feed, unclean housing, proximity to calving, or the presence of some other disease factor, with Mycoplasma bovis symptoms developing as a secondary disease.

If there is one ray of good news out there, it is that dairy industries in other countries do manage to prosper despite having Mycoplasma bovis.  If eradication is not possible, then we will, over time, learn how to manage the disease under our New Zealand conditions. Mycoplasma bovis will continue to be a big nuisance, and some farms will be hard hit, but it is not going to destroy the industry.

*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.