The pathology and haematological changes in experimental Pimelea spp. poisoning in cattle ("St. George disease")

Six young cattle were intoxicated with either stem or extracts of stem of Pimelea trichostachya or P. continua. Oral dosage with whole plant or alcoholic extracts was shown to reproduce all the clinical and pathological features of the various field syndromes known collectively as "St. George disease". Subacute intoxication resulted from relatively high oral dose rates, of the order of 60 mg of whole stem/kg body weight/day, maintained for about 2 weeks. Diarrhoea, weakness and anaemia were the predominant features of this sundrome. Lower dose rates, regulated according to the severity of diarrhoea, eventually produced signs of circulatory failure (subcutaneous oedema, hydrothorax and cardiac dilatation) in addition to anaemia and diarrhoea. It did not prove easier to produce circulatory failure by intranasal insufflation of powdered plant. Although the bone marrow of most affected calves did not react to the anaemia there was some evidence that erythropoietic tissue was not directly damaged during the intoxication.