About 340,000 chickens are to be slaughtered on eight Kam Tin farms in the biggest single cull of the current bird-flu outbreak. The slaughter, to be completed by Friday, will bring to 860,000 the number killed since the outbreak began on February 1. Although bird flu has not been confirmed on the farms, the cull was ordered as a precaution since the properties are inside the Kam Tin quarantine zone. Fifteen farms inside the zone have been confirmed with the disease. The Director of Agriculture, Fisheries and Conservation, Thomas Chan Chun-yuen, said: 'We are very confident that by culling the chickens in the Kam Tin quarantine area, we will have got rid of the disease.' The decision to kill all chickens on the eight farms came after two chickens were found on Monday with suspected H5N1 flu infections. Mr Chan said the farms would be cleaned and emptied of birds and would resume breeding only after tests proved the virus was eliminated, a process that would take at least three weeks. He defended the decision to continue the slaughter 19 days after the outbreak began. 'Not all chickens are affected on the same day - some earlier, some later - and checking and verification needs time.' Mr Chan will head a seven-member investigative team to probe the causes of the latest outbreak of H5N1, the SAR's third in four years, and propose more anti-bird flu measures. Their report is expected in six weeks. Dr Liu Kwei-kin, deputy director of the Agriculture, Fisheries and Conservation Department, said: 'The pathogen has to be brought into the farm but that pathogen can be carried in a variety of ways and all these have to be ascertained in the course of the investigation.' Malik Peiris, a microbiology professor at the University of Hong Kong and a member of the Government's expert flu team, said yesterday it was felt that slaughtering the rest of the Kam Tin farm chickens was 'the best measure' to stamp out the source of the latest infection. But chicken farmers yesterday said farms involved in the outbreak and slaughters were facing combined losses of $20 million. One farmers' representative said it would take, on average, nine months before the farms could resume business. 'The Government is obviously trying to break our livelihood. The remarks by officials give us an impression they want all local chicken farms to close down,' he said.