Complex cattle network discovery reveals disease risks

Half of all British cattle farms were connected to more than 1,000 other farms every year when they bought cattle

As the buying and selling at cattle auctions plays out each week, data is building up, and it is not related just to the exchange of money.

A new study by researchers at the University of Exeter in the United Kingdom profiled the buying and selling of beef and dairy cattle.

It analyzed a network of all contact chains each farm became associated with because of the purchase of a single cow.

Researchers analyzed the buying and selling patterns on British farms using official records of 75 million movements of cattle between farms from 2001-15.

In a 12-month period of trading, they were able to show that about half of all British cattle farms were connected to more than 1,000 other farms every year when they bought cattle and 16 percent of farms were connected to more than 10,000 other farms in a single year.

The importance of the research is not only the significance of trade but the implications of the spread of disease. The research could help identify potential routes of infection and therefore provide information on potential ways to improve disease control strategies.

“My PhD project focuses on the concept of farms as super spreaders of infection,” said researcher Helen Fielding. “One of the most likely mechanisms by which they might be able to do this is via cattle movements so that prompted us to use the network analysis approach based on the comprehensive data set that was available to us.”

She said the amount of data — 75 million movements — intimidated her at first. While she had some information on imports and exports, the study was kept at the country level, concentrating on farm-to-farm links within Great Britain.

British farmers know that trading cattle can bring risks of disease transmission.

Fielding said infection risks were often thought to have been from the most recent farm that sold the animal. But her team looked further back in the trading network, given that the animals being bought might have been exposed to many more environments and pathogens than first thought.

In reality, if a farm bought cattle from one or two farms, they might actually be at the end of a chain that connected their new cows to several thousand other farms.

As an example, she said that a farm in Devon bought six cattle in one year. Those six came from four farms but those farms were connected to 10 other farms. Those 10 were further connected. Tracking through the data over 12 months, Fielding’s team traced the links from the Devon farm to 11,132 farms scattered from Kent to North Wales to Orkney.

On average, more than 13,000 farms had contact chains involving more than 10,000 other farms whether buying or selling in any single year during the study period. These farms could be particularly exposed to infections and therefore were able to spread them forward.

“Our study was based on the premise that if any two cows were on a farm at the same time for more than one day, there was the potential to transmit disease,” said Fielding.

She added there were many cases where this assumption did not reflect reality, such as if the farm quarantined new animals for a time before introducing them to their new herd. She added that this practice is rare in Great Britain on commercial farms. Other farms might keep animals in separate management groups, further limiting the disease spread potential, she said.

The work reinforced the value of biosecurity, surveillance, vaccinations and quarantine procedures.

“Most farmers are surprised that the industry is so closely connected,” said Fielding.

Further study was ongoing, she added.

The study was published by Royal Society Open Science.

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