Cerebellar ataxia in sheep grazing pastures infested with Romulea rosea (onion grass or Guildford grass)

There have been anecdotal reports since 1962 of 'staggers' in sheep grazing Romulea rosea infested pastures, but this is the first detailed account. In September 2005, a locomotor disorder developed in 12 of 120 Merino wethers that had grazed R. rosea infested pasture at Albury, New South Wales, over several months. Affected sheep displayed signs that included limb paresis, knuckling over in the fetlocks, fine head tremor, incoordination, and an equilibrium disturbance characterised by frequent falling. The microscopic examination of brain and spinal cord tissues from two affected sheep revealed mild vacuolation, occasional lymphocytic cuffing around blood vessels, mild Wallerian degeneration, and occasional glial cells that contained honey-brown cytoplasmic pigments. The most significant changes were found in the cerebellum, where there were decreased numbers of Purkinje cells, increased numbers of glial cells, scattered vacuoles and occasional swollen axons. Previous reports of cerebellar toxicoses in ruminants have involved goats and cattle and have been associated with the ingestion of six Solanum spp. The Purkinje cell loss in this type of disorder is ultimately extensive and consequently affected animals may survive, but will remain permanently disabled.