Valsiekte (falling disease): a nervous disorder in lambs suspected of being caused by the plant Chrysocoma tenuifolia.

A description is given of the clinical signs and pathological changes in 23 field cases of valsiekte from the Bethulie region of the Orange Free State, Republic of South Africa. The disease, which occurred almost exclusively in 2-4 month-old Dorper or Dorper cross-bred lambs, was characterized by protracted ataxia, paresis and high mortality. Microscopical changes were consistently found in the neurons and white matter along the entire length of the spinal cord, and rarely in the medulla oblongata. These changes included vacuolation and degeneration of neurons, mainly of the lateral and ventral horns in the spinal cord, and a status spongiosus which was most noticeable in the lateral and ventral tracts of the spinal cord. All affected lambs had access to the plant, Chrysocoma tenuifolia (bitterbos), but trials to reproduce the condition by dosing the plant, were not successful.