Reproduction of progressive retinal degeneration (bright blindness) in sheep by administration of ptaquiloside contained in bracken.

The process of occurrence of bright blindness, progressive retinal degeneration (PRD), in sheep was observed using two Suffolk ram lambs fed on a diet containing bracken powder. The first sign of the bright blindness was detected 4 months after the start of experiment. Based on these preliminary results, the amount of bracken powder necessary to induce PRD was estimated (experiment I). In the following experiment, ptaquiloside (PT), a norsesquiterpene glucoside of the illudane type isolated from bracken, which is a bracken carcinogen and a causative principle of cattle bracken poisoning was administered to two Suffolk ram lambs. It was clearly demonstrated in this experiment (experiment II) that PT present in bracken is also a causative principle of PRD.