Dutch Ministry of Agriculture officials began culling 25,000 chickens at a farm in the province of Gelderland on Wednesday morning after a mild form of bird flu was detected there, Dutch news agency ANP reported.
The culling team followed advice from the Animal Protection Society (APS) on how best to gas the poultry.
"A gas pipe will be positioned in the center of the barn and branches will run from there to other parts of the building. This spreads the gas evenly," a Ministry spokesperson was quoted by ANP as saying.
The farm will be fully disinfected after the culling and removal of the poultry.
The culling operation was originally scheduled for Tuesday afternoon but was postponed when the APS called for it to be done in a more humane way.
"In the last outbreak in 2003 they sealed off the sheds and blew in the gas from one side. Afterwards, all the chickens lay piled up in one corner. They had climbed on top of each other to escape and suffered cruel death by suffocation," an APS official said.
The poultry farm near Voorthuizen in Gelderland was sealed off on Tuesday after traces of bird flu were detected there.
Virologist Ab Osterhaus stressed the traces were of a mild form of the avian flu. This variant is far less virulent than the one that led to the culling of millions of chickens and other poultry in the region in 2003.
The Ministry of Agriculture imposed a ban on the transportation of live or dead poultry, eggs or feed within a three-kilometer zone around the factory. Shipments of pigs and cows are also prohibited if the destination is a firm within the zone.
Other poultry farms in the region have been ordered to take measures to ensure visitors do not come into contact with poultry.