Experimental evidence is presented to confirm field observations that Asaemia axillaris (Thunb.) Harv. ex Jackson and Lasiospermum bipinnatum (Thunb.) Druce cause ovine hepatogenous photosensitization. The two plants have fairly distinct distributions. While Lasiospermum is most prevalent in theeastern Karoo, Asaemia is commonest in the west and, except perhaps in the southern central Karoo,they seldom occur together. The locality of an outbreak should therefore be taken into account when making a diagnosis. Peripheral fatty changes and midzonal necrosis of liver lobules were seen in both Asaemia and Lasiospermum poisoning. Asaemia poisoning could, however, be distinguished from Lasiospermum poisoning by the presence of centrilobular fatty degeneration and the absence of haemorrhages and bile pigmentation. Although it may be difficult to distinguish between the two types of plant poisoning they are easily differentiated from geeldikkop (a major photosensitizing disease of the Karoo), which lacks a zonal pattern of hepatocytic degeneration and necrosis. Moreover, the crystalloid material characteristic of geeldikkop is not encountered in Asaemia or Lasiospermum poisoning.
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