Counting cost of cow disease
Over the past few months, everyone in New Zealand has been on a steep learning curve about the cattle disease mycloplasma bovis, and all of us will be paying the price of countering its arrival here.
Among the decisions that Agriculture Minister Damien O’Connor has had to make was this week’s call on whether to seek to eradicate or manage the disease. Over the next ten years, it was always going to cost a billion dollars, either way.
The differences might be more apparent than real, anyway. Managing M. bovis would still entail eradication at the margins, as a containment measure.
Encouragingly, all of the 39 properties where the disease has so far been detected have been connectable via movements between the infected herds, all of which occurred before the initial discovery in July 2017. Optimistically, that could indicate the disease is not spreading, may conceivably be contained and could possibly over the long haul, be eradicated.
The movement of infected animals has been the main form of transmission, which can occur via animals, machinery, cattle semen, or even soil – which in the right (ie wrong) moist conditions can keep bacteria active for up to 50 days.
There is no effective vaccine against M. bovis. Unfortunately for all concerned – including the cows –there is no test that can detect M. bovis on an individual animal basis. Tests can confirm an animal has the bacteria, but not if it hasn’t. Therefore, if one cow has the disease the entire herd must be assumed to be infected, and culled.
Early diagnosis is difficult, since the symptoms can appear along a clinical spectrum from non-apparent to severe.
Given all these attributes, M. bovis tends to be extremely difficult to intercept at the biosecurity border. This is likely to pose problems in proving the culpability of any individuals prosecuted for the outbreak, since the accused could legitimately claim to have introduced the disease in all innocence, by accident.
As MPI officials confirmed last week, the strain detected here appears to have come from Europe (not Australia) and the outbreak’s point of origin has been traced to a farm near Winton, in Southland. By last week, MPI had traced ‘‘high risk animal movements’’ to 3000 farms.
One nagging problem with the outbreak has been that around 70 per cent of farm-tofarm transfers of animals are undocumented in NAIT (New Zealand’s cattle and deer tracing system). Officials have been forced to rely on notes taken by farmers, and on their memories of animal movements in and out of their properties.
Testing of bulk milk supplies has provided amore reliable means of tracing the paths of infection. Clearly, more rigorous track and tracing systems are going to be required of farmers in future, if only for their own protection.
Changes to day-to-day farming practices in New Zealand are inevitable, O’Connor says.
‘‘Most farmers who have studied this realise they will need to have amore closed farming system. There will less off farm grazing, less movement of stock, more dependence upon their own breeding regime for replacement stock, and better management of their milk and surplus milk in particular. And better record keeping.’’