M. bovis: More Questions Than Answers

The More We Know, The More We Don't Know About Cattle Disease

Written by Rebecca Glover

What do we know about Mycoplasma Bovis?

It's probably fair to say there's more we don't know than what we do. Where, when, how are questions that are still not answered, or are given different interpretations every week. And every week more comes to light about the disease, prompting still more questions.

For those who have been hiding under a rock, or behind their latte, for the last year, M bovis is a cattle disease new to New Zealand. It poses no threat to human health – milk from an infected cow won't spoil the latte, and a steak from an infected animal is as safe as any other. It's already well established in most of the rest of the world, except Norway. However, the disease is a significant animal welfare and production problem in affected herds, and for those whose animals are compusorily culled there are massive financial and psychological upheavals, causing some to leave the industry.

M bovis is a bacterial disease with symptoms including abortions, untreatable mastitis in dairy and beef cows, severe pneumonia and ear infection in calves, and swollen joints and lameness in all ages of cattle. While some of the conditions can be treated, affected cattle will always be carriers of the disease.

The biggest risk for the spread of M bovis is through direct animal contact, including those that are infected but may not be showing symptoms. It is not windborne. Feeding infected milk bears the second highest risk of spreading M. bovis. The disease does not affect other animals although it is thought goats could carry and transmit it.

Mycoplasma has been called the worst economic pest or disease to arrive in New Zealand. The government decision to attempt to eradicate it from New Zealand means all cattle on infected farms and future infected farms, plus some high-risk farms under movement controls, will need to be culled; about 126,000 cattle from about 190 farms, in addition to the 26,000 already culled. The timing of any cull will be worked through with individual farmers to minimise impacts on production.

The cost of eradication has been estimated at $886 million over 10 years, but this path has been chosen, in consultation with New Zealand and overseas experts, as being preferable to attempting to manage it.

In an RNZ interview, Dr Helen Beattie, New Zealand Veterinary Association's chief veterinary officer, said “Eradication...could take years to achieve because infected animals might have no signs of illness and the bacterium is hard to identify through testing. Testing is tricky and the results are inconclusive.

“M bovis is hard to see, hard to test for, and hard to treat. Even for veterinarians, M bovis can be hard to diagnose. You don't always see clinical signs, or if seen, they can look like other diseases. Antibiotics aren't very effective in treatment of the disease. Culling infected animals is generally the only option.”

The question that most farmers would like answered is how the disease got into the country. Is our border security too lax? Do large corporate farms have the ability to sidestep regulations for importing bull semen, embyros or animal remedies? Other possible pathways include imports of feed, used farm equipment, and live cattle.

When it arrived is another bone of contention. The Ministry for Primary Industries (MPI) is adamant that M bovis arrived late 2015 or early 2016, but many people believe it was here earlier, including Keith Woodford, a former Lincoln University professor and prolific writer on the subject. Every long term calf rearer has struck the occasional calf with pneumonia, arthritis or other infections which have not responded to treatment, and they may well agree.

Woodford believes the shadow of M bovis will affect the calf rearing industry in the short term as rearers struggle to ensure their calves have been fed safe milk.

Many rearers who have been using 'waste milk' unfit to go into the vat will also need to examine their practices. Milk from cows under treatment for mastitis or other illnesses should be discarded. These cows are more likely to shed M bovis into their milk than healthy cows.

With cattle from confirmed M bovis herds now widely distributed throughout the country, traceability increases in importance.

“Crucial to us being able to control the disease and respond appropriately is the National Animal Identification and Tracing scheme (NAIT). Under this scheme, individual cattle are tagged so their movements can be traced - including in the event of a disease outbreak,” says Helen Beattie, who along with others blames farmers for not using the system properly. Figures of 85%-90% noncompliance have been quoted, with little to no evidence to back this up. Many farmers regard NAIT as an imperfect system, not always userfriendly and sometimes with a mind of its own with regard to information recorded. In the early years of NAIT, movements of animals less than a month old off-farm were not required to be recorded, resulting in the registration of calves at farms where they had not been born. Improvements are apparently in the pipeline, however, including a possible cellphone app.

How safe are saleyards? DairyNZ's Nita Harding advises avoiding buying from saleyards because of the cattle mixing that occurs there, suggesting that farmers trade amongst each other privately instead.

PGG Wrightson's general manager livestock, Peter Moore, disagrees.

“Saleyards have a very high compliance with NAIT, and all stock must be accompanied by an Animal Status Declaration form. We rely on farmers' honesty in filling in the forms correctly, and it is a legal document. There should be no animals from movement controlled farms arriving at saleyards anyway. If everyone does their bit we should be no better or worse off than before – the saleyards are as safe as ever.”

Parents poised to purchase calves for school calf club days are advised by MPI to “look for alternatives to calf day. It could become a ‘pet day’ with other pets and animals, or you could use technology to provide an innovative compromise.” A virtual calf, perhaps?

Uncertainties abound. Off-farm grazing of dairy heifers may be reduced as farmers look to implement closed systems. Questions have been raised over the future of sharemilking. A&P shows and the use of service bulls for the dairy industry are likely to be affected by disease fears, although bull sales to date have been going well.

One aspect has been clarified though. Previously believing themselves constrained by the Privacy Act, MPI has now decided to start directly informing neighbouring farms when an infected or high-risk property is detected nearby.

In the immortal words of Donald Rumsfeld, a former US Secretary of Defense:

“As we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns - the ones we don't know we don't know.”

Seems to sum up the situation pretty well.