Bog asphodel (Narthecium ossifragum) as a cause of photosensitisation in lambs in Norway.

In a five year experiment, 195 lambs and their dam were kept on four plots of wet moorland rich in the plant Narthecium ossifragum. The plots were top-dressed with calcium and, or, phosphorus, or given no treatment. After three years, the plant disappeared from the plots to which phosphorus had been applied, but remained where calcium only had been used. The saponin content of the plant appeared to be uninfluenced by the type of top-dressing or time of year. Photosensitisation (alveld) occurred on all plots during the first three years. During the fourth year the disease occurred only where the plant persisted. In the fifth year the disease did not occur on any plot. Alveld was produced in two lambs by the repeated administration of large quantities of saponin preparations from N ossifragum. Lambs of haemoglobin type AA were significantly more resistant to the disease than lambs with type BB. In nearly half the cases, the bromsulphthalein liver function test indicated a susceptibility to alveld up to seven days before the appearance of clinical signs. Increased bromsulphthalein retention was more common amongst AA lambs than BB lambs, but nearly all the BB lambs developed alveld, and only a few of the AA lambs. The differences were significant.