The Swiss government said on Wednesday that it would lift the two-and-a-half month outdoor ban on poultry as of May 1, thanks to the reduced risk of bird flu.

It is now safe for farmers to allow their chickens outside again since not a single case of avian flu has been reported this month, said a government statement.

The outdoor ban - the second in 12 months - was introduced on February 20 to reduce the risk of Swiss poultry coming into contact with virus-carrying wild birds.

The government said the situation had now eased since most migratory birds, which have been spreading the disease, had flown north to their summer breeding grounds.

It added that the last remaining surveillance zone in the country, around Lake Constance, would probably be lifted before next week.

Several of Switzerland's 32 bird flu cases, all affecting wild birds, were discovered on the lake's shores. Nationwide, the Federal Veterinary Office has confirmed nine cases of the deadly H5N1 strain.

The virus was first identified in the country in February and more than 1,000 birds have since been examined by the authorities.

The government said it reserved the right to re-introduce surveillance zones and protection measures if any new cases of bird flu are found. Hwever, it did not say it would call again fora nationwide outdoor ban.