COWS on dairy farms are five times as likely to catch foot and mouth disease
as those on farms rearing beef cattle, say vets who analysed patterns of FMD in
Cumbria, one of the “hot spots” in Britain’s recent epidemic.
The vets say the difference should be factored into mathematical models used
to predict the course of epidemics and recommend control measures. “As far as we
in the field are concerned, this was pretty obvious,” says Sam Mansley, head of
epidemiology for North England and South Scotland at the government’s Animal
91É«ÇéƬ Office in Carlisle. “It concerned us that it had been missed out of the
models used this time.”
Mansley, Nick Honhold and team leader, Nick Taylor of the University of
Reading, report in The Veterinary Record (vol 17, p 600) that only a
fifth of Cumbria’s cattle farms are dairy. Yet they accounted for 58 per cent of
Cumbria’s infected farms. And FMD hit 37 per cent of Cumbria’s dairy farms,
compared with only 7 per cent of beef cattle farms, making them five times more
at risk of contracting the disease.
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Dairy farms are probably more at risk because there is a greater movement of
animals, people and machinery than on beef cattle farms, says Mansley. “Cows are
collected twice a day to be milked, and the milk tanker visits each day.” And as
“producer animals”, they might be more stressed and susceptible to infection
than beef cattle. “It’s not rocket science,” he says.
Epidemiologists whose predictions shaped the government’s control measures
say they need more data. “I’d like to have a scientific discussion of these
issues once it’s published in a peer reviewed journal,” says Mark Woolhouse of
Edinburgh University, head of one of the three key teams of modellers. He says
the authors have yet to reply to his own request for more information. He also
says that, in general, dairy farms are bigger, and the size of farms was a key
factor fed into the models.
Christl Donnelly, a key member of another modelling team at Imperial College,
London, echoed this, saying that in Cumbria, two-thirds of dairy farms have more
than 100 cattle. Only a quarter of non-dairy farms have that many.
