An extract of a natural bloom of the blue green alga Microcystis aeruginosa was administered to groups of 7-day-old layer and broiler commercial chickens as a single oral dose. The LD50 values ranged from 1295 to 1643 mg of freeze-dried algal bloom per Kg of chicken. The toxin was principally hepatotoxic causing massive hepatocellular necrosis and biliary hyperplasia in lethally affected chickens. Lymphoid necrosis was seen in the bursa and spleen. The intraperitoneal LD50 of the bloom in chickens and mice was determined to be 13 and 19 mg of freeze-dried bloom per Kg of chicken and mice respectively.
