More than 400,000 hens will have to be culled at a farm in Codigoro, in the province of Ferrara, after the discovery of an outbreak of avian influenza, a disease that has killed millions of birds worldwide in recent years. The culling of the hens was decided by the Ferrara Health Authority after verifying how widespread the outbreak was within the farm of the Eurovo company, one of Europe's leading egg distributors. The risk of an outbreak had been reported by the farm employees themselves after finding several dead hens and others with respiratory difficulties. An abnormal thickness of the eggshell, which was very thin, had also been noted. In other cases, the shell had not formed at all. Officials from the Ferrara health authority took action on Friday: biological samples were taken, then sent to the Experimental Zooprophylactic Institute of the Venezie, in the province of Padua. The tests confirmed the presence of avian influenza.