Livestock genetic companies are adamant their bull semen is not responsible for bringing in the disease Mycoplasma bovis, but former Federated Farmers president Dr William Rolleston says farmers need more proof.
He said until the semen and/or the donor bulls had been reliably tested as negative by the Ministry for Primary Industries (MPI) or an independent lab, the possibility of the disease entering New Zealand through semen “must remain open”.
The disease, highly contagious within herds but not from farm to farm through airborne means, was detected for the first time in New Zealand in July on two farms owned by South Canterbury farmers Aad and Wilma van Leeuwen.
Mycoplasma bovis is in all of the world’s dairy countries. It does not infect humans and presented no food safety risk. There is no concern about consuming milk and milk products.
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Some animals from the van Leeuwen properties have already been put down for animal welfare reasons, while others are being sent to freezing works for slaughter.
One of the world’s largest semen companies, US genetics firm World Wide Sires said it was “pleased MPI has confirmed there is no evidence that resistance has developed to Mycoplasma in imported bovine semen”.
World Wide Sires New Zealand general manager, Hank Lina, said the company – along with other importers of bovine semen – had been working with MPI to isolate and identify the source of the outbreak.
“We sell more than 19 million straws of semen to 80 countries around the world and, over several decades, have developed semen production and processing procedures which are amongst the most rigorous in the world,” Lina said in a statement.
Lina said World Wide Sires began research on fresh semen programmes nearly two decades ago. It had been frustrated at the ability to grow and culture Mycoplasma and the long interval necessary for results when it was assessed by culture.
One of its scientists had developed techniques to detect Mycoplasma bovis in semen. She developed efficient methods for growth, culture, DNA extraction, and PCR based detection.
“No evidence of mycoplasma bovis was found in any of World Wide Sires’ 1700 bull team either during the research programme, or since,” Lina said.
The company also used a wide range of antibiotics as a secondary line of defence against contamination.
Lina said all semen companies had been required to provide batch numbers and details of all bovine semen imported to New Zealand and potentially supplied to the van Leeuwen group. He commended MPI for its rigorous approach.
Senior advisor for MPI’s animal imports team, Angela Snell, said initially researchers believed the disease spread through infected animals, but now there was “a strong international view” that semen could become contaminated if infection was present on the bull’s reproductive tract at the time of collection.
“However, when standard collection hygiene is practised, reports indicate that bacteria are not observed in semen. While there are several references in the literature that show that M. bovis can be demonstrated in semen and that it can remain viable when frozen for long period, there is little scientific information suggesting this as a route of transmission to cows,” Snell said in an email.
Antibiotics were also used to kill the disease, although “Mycoplasmas are notoriously difficult to treat with antibiotics, and antibiotic resistance must be considered”, she said.
Rolleston, who farms in South Canterbury and runs a hi-tech animal blood products company, attended the MPI meeting for farmers last week.
He said his analysis was that the companies were admitting the risk of it coming in through imported semen was small but did not rule it out completely.
“We have to keep an open mind on all pathways and MPI should not dismiss semen as a possible pathway until the semen/bulls have been tested negative to M. bovis. This is not a witch hunt it is simply going through the process in an objective manner,” he said.
One of the problems with testing was that companies might not be willing to conduct the tests because under the Import Health Standard developed through the World Trade Organisation, they did not have to.
Because every country had the disease (except New Zealand until recently), any testing for M. bovis was regarded as a barrier to trade.
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