The Dutch government has ordered the culling of 600 ducks after routine blood tests showed signs of antibodies to a mild strain of bird flu.
The agriculture ministry said it had ordered the cull on a farm in Lopik in the central province of Utrecht after antibodies showed up that could indicate the birds were in contact with the contagious virus.
A follow-up test did not confirm an outbreak of bird flu, but a further test was not able to rule out a mild strain of the virus.
On Saturday, the government decided to cull 22,000 chickens at a farm in Eemsmond in the northeast of the country as a precautionary step after blood samples taken there also indicated birds had developed antibodies to the virus.
Two neighbouring poultry farms as well as a third company, owned by relatives of the Eemsmond farm, were still under investigation although early tests were all negative. The results of further tests will only be available in 10 to 14 days.
Last year a mild form of the virus mutated into an aggressive variant, leading to the slaughter of a quarter of all Dutch poultry at a cost of hundreds of millions of euros.
The European Union's largest poultry exporter slaughtered 30.7 million birds at some 1,300 farms to contain the outbreak of the virus that led to one human death.
Avian influenza has spread across much of Asia in recent months, killing at least 15 people in Vietnam and seven in Thailand.