East Anglian poultry producers are preparing for the worst after a meeting to discuss avian flu set up by the National Farmers' Union (NFU).
The industry has about 21m birds in East Anglia
At a Peterborough summit, Defra warned that if a single bird became infected, the whole flock would be slaughtered.
The meeting was organised on Monday as it was revealed quarantine measures were being reviewed after a parrot died from avian flu in a compound in Essex.
NFU believes the region has the UK's largest concentration in the industry.
Monday's summit was called by poultry farmers to try to reduce the impact of any outbreak.
The region produces 25% of chickens consumed in this country, employing thousands of people. There is an estimated 21 million birds in East Anglian flocks and all but four million are for meat production.
At the meeting there was the reassurance that the risk of mass infection was low but the emphasis is on prevention - what the industry calls bio-security - and poultry farmers were advised on Monday to report suspected cases of bird flu to Defra immediately.
Alison Pratt, of the NFU, said many measures were in place that they hoped would stop the disease from arriving in the UK.
"And, of course, producers are on the lookout for any bird that looks a little bit off in the weeks and months to come," she said.
But chicken farmer David Mills warned against blowing things "out of proportion".
"We've faced diseases before and through good management kept them under control and continued producing good quality British food," he added.
The meeting also heard how free range chickens might have to be taken inside should there be an outbreak of bird flu.
Defra veterinary manager Sarah Gordon admitted that all chickens in the country could not be accounted for as many people kept small numbers of birds in their gardens.
But resources would be put into finding them quickly if the need arose, she added.
Wild bird deaths
The meeting heard another casualty could be poultry markets with a ban on livestock meetings being considered by Defra.
Dr Graham Lewis, Defra's deputy head of exotic disease prevention and control, said the department was working with the RSPB and the Wildfowl and Wetland Trust to keep tabs on wild birds.
He said: "We are discussing the migratory routes and fly ways to see whether any parts of the UK are at greater risk than others."
The Veterinary Laboratory Agency was investigating the deaths of several wild birds to see if avian flu was to blame.