health & science
M. bovis semen call ‘premature’: MPI
The Ministry for Primary Industries isn’t ruling out that the cattle disease Mycoplasma bovis arrived in New Zealand by European-sourced semen. David Williams reports.
It’s “premature” to zero in on imported bull semen as the likely source of the cattle disease Mycoplasma bovis, the Ministry for Primary Industries says.
Last week, Lincoln University honorary professor of agri-food systems Keith Woodford said it was “increasingly evident” that legally-imported European-sourced semen was the likely source of the disease – and that it struck first in Southland by late 2014 or even earlier.
While MPI response director Geoff Gwyn doesn’t rule out European-sourced semen as the source, he says it’s one of just seven potential entry pathways for the disease being considered. He tells Newsroom: “Mr Woodford is premature in his assessment of it being the likely source.”
(Gwyn didn’t answer questions about what testing is done on frozen imported semen and whether that testing would be scaled up.)
MPI’s pathways report, produced in late November, didn’t reach a conclusion about the likelihood of any of the potential sources – imported frozen semen, imported live cattle, other imported animals, imported embryos, imported veterinary medicines and biological products, imported feed, and imported used farm equipment. Gwyn: “MPI continues to examine potential entry pathways.”
As to Woodford’s claim that M. bovis arrived in New Zealand in 2014 or earlier, Gwyn says: “All of the evidence that MPI has gathered to date points to Mycoplasma bovis arriving in New Zealand in late 2015 or early 2016. This conclusion has been arrived at as a result of tracing analysis and, importantly, analysis of the DNA evidence.”
“This does not constitute proof, but it does provide a pointer.” – Keith Woodford
What Gwyn doesn’t say is that a pilot study, mentioned in last November’s pathways report, found M. bovis DNA in straws of imported semen from an affected property. The report said the study, which had a small sample size, wasn’t conclusive proof of that potential method of transmission. No “viable” M. bovis was present, the report said, only the DNA was.
What viable means, according to Woodford, is the DNA couldn’t be cultured in a test tube, which suggested it had been killed by antibiotics. “But it would only have taken one faulty batch for it to have slipped through.”
Woodford, a prominent agricultural consultant, has form for getting things right. In March, he told Newsroom it was “highly likely” M. bovis – first discovered in South Canterbury, had been in Southland first, perhaps as early as 2014. Last month, MPI confirmed the disease has been traced back to a single farm in Winton, Southland.
Suspicions about imported semen being the likely source, according to Woodford, were because “no other single source can explain the range of infected properties”. He found three infected Canterbury farms that lacked “obvious live animal links” to the two farms with the strongest links to infected farms – Van Leeuwen Dairy Group in South Canterbury and Southern Centre Dairies in Southland. All of those farms used the same Northern European semen, Woodford wrote.
“This does not constitute proof, but it does provide a pointer.”
The Government has announced an ambitious, $886 million plan to try and eradicate the disease, which was first identified in New Zealand on a South Canterbury farm in July last year. MPI, which has been wrestling with privacy issues, is now taking a zero tolerance approach to compliance with National Animal Identification and Tracing (NAIT) scheme.
Last week marked the first time a Wairarapa farm – a sheep and beef farm near Masterton – was confirmed M. bovis-positive. That took the number of infected farms in the North Island to three, as of last Friday, with 33 in the South Island. A further 162 properties are under movement restrictions.
Twenty-eight infected farms have already had their cattle culled – in all, 24,384 animals have now been slaughtered because of the outbreak. About $7.6 million in compensation claims have been paid.
MPI modelling predicts 142 farms will have to be depopulated in the first year of New Zealand’s phased eradication of the disease, leading to an expected $180 million in compensation payments.
M. bovis doesn’t present a food safety risk – the meat from infected cattle can be safely eaten by humans. But the highly contagious bacterium causes cattle to get ill, with symptoms including mastitis, abortion, pneumonia and arthritis.
While New Zealand is trying to eradicate the disease, other countries have learnt to manage it.
M. bovis has been in Australia since 2006. By one 2014 count, up to 3.5 percent of dairy herds in the country’s south-east were infected. A Dairy Australia fact sheet produced last year says environmental stresses – like poor weather, bad nutrition or poor management practices – can precede outbreaks.
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