Defra has also raised the status of its cull at another farm owned by Gressingham Foods, Grove Farm, from precautionary to slaughter on suspicion after a second suspected outbreak was found.
The cull on the original site, Redgrave Park farm should now be complete and culls are now underway at Grove Farm and will be followed by Hill Meadow Farm.
Up to 22,000 birds are now being culled on five farms, all within the AI control zone.
Geoffrey Buchanan, operations director, said: "We have learned that Defra is raising the status of the cull at Grove farm from precautionary to slaughter on suspicion. Defra's vets found about 0.5% loss in the flock at Grove farm yesterday. It is worth noting that a normal aspect of production is the loss of a small proportion of birds.
"Given the direct link between the Grove and Redgrave Park farms through the shared workforce, this was sufficient to raise the status.
"To date, Defra's tests have not shown any evidence of avian influenza at any of the five farms other than Redgrave Park. We hope to know by tomorrow morning if Defra's tests find avian influenza in the samples taken at Grove farm.
"We would also like to respond to some of the speculation about the cause of the outbreak. We know of no direct link with the Netherlands and the five farms involved. All of our turkey poults and the feed are from the UK. The geese and ducks at Redgrave Park farm were also from the UK."