Around 3.8 million chickens have been slaughtered as part of the effort to contain a bird-flu outbreak in the western state of Jalisco, Mexico's food safety agency said.
More than 9.3 million other birds remain under observation, the agency said.
The virus was detected at 33 of the 253 Jalisco chicken farms inspected by the agency and 82 were found to be free of bird flu, while "diagnostic processes continue" at the other 138 facilities.
Senasica said it has also begun to look at farms outside the two municipalities where the bird flu outbreak was detected last month.
The outbreak claimed 2.5 million chickens in the first three weeks and generated $50 million in losses, a representative of the Mexican poultry sector said last week.
Around 32,000 jobs could be lost if the virus is not immediately brought under control, according to Ricardo Estrada, president of the Poultry Farmers Association in Tepatitlan, Jalisco, one of the affected municipalities.