Health and animal experts expressed shock at the news Friday that a chicken farm in Tanba, Kyoto Prefecture, did not notify officials that thousands of its birds had died despite mounting bird flu fears.

The incident highlights the difficulties involved in trying to contain an infectious disease when announcing that a farm is affected is virtually certain to cripple its business.

"To be honest, my first reaction when I heard was, 'You must be kidding!'," said an official at the Agriculture, Forestry and Fisheries Ministry after learning of the delay in notification. "The first rule in dealing with contagious diseases is to inform authorities as soon as anything out of the ordinary happens."