M. bovis suspect imported semen – Norway study

The study, ‘Semen as a source of Mycoplasma bovis mastitis in dairy herds’, is published in Veterinary Microbiology, March 2018.

“To our knowledge this is the first study describing the introduction of M. bovis infection into a naive dairy herd via processed semen,” say the Norwegians.

“The antibiotics used in semen extenders should be re-evaluated in order to provide farms with M. bovis-free semen, or tested M. bovis-free semen should be available.”

The researchers found that M. bovis was introduced into two dairy herds via contaminated semen used for artificial insemination. They were able to identify the bacteria in straws of frozen semen, and traced both farms’ infections to a single infected bull.

Describing the farms as “closed and adequately biosecure,” they say their epidemiological analysis did not find any significant route of infection other than semen.

Although Norway has been cited -- along with NZ -- as previously free of the disease, the researchers said it had first been identified there in late 2012. But its relatively low prevalence meant that transmission by “less common sources” could be better studied there than in high prevalence countries.

In October, the US National Association of Animal Breeders (NAAB) had said that while there were reports in scientific literature of M. bovis transmission in unprocessed bovine semen, there had been no documented reports of transmission by the commercial use of frozen semen. 

NAAB protocols call for a cocktail of antibiotics in the extended semen, and the use of only frozen semen, because fresh semen would require more or stronger antibiotics, which would then have a spermicidal effect.

Hank Lina, general manager of World Wide Sires NZ, whose American parent company is a NAAB member, emphasised that it had supplied 50 million straws without a known case of M. bovis infection.

In NZ, MPI has prepared a Pathway Tracing Report looking into the various possible sources of the outbreak. Although it was complete before Christmas 2017, its public release was delayed to coincide with a report by an international technical advisory group asked to evaluate NZ’s response to the outbreak.

MPI response coordinator David Yard declined to comment on the Norwegian study but said the reports would be fully in the public domain “in a couple of weeks”. 

“It’s quite unusual that we do this, but I think it is important that we do this.”

MPI had already largely acted on the advisory group’s recommendations to improve on the response, he said.