A friend has eight 6 month old hens, 6 Isa Browns and 2 barred rocks. All have been laying and eating well. But a few days ago he noticed blood on their bedding and found all 6 isa browns had bloody rear ends. One died. The 2 barred rocks are fine. No evidence (to him, at least) of pecking. All 6 were stricken at the same time.