Experimental intoxication by Myoporum laetum in cattle.

Myoporum laetum was collected in the counties of Rio Grande and Capao do Leao in winter and in Santa Vitoria in summer, autumn, winter and spring, in the state of Rio Grande do Sul and in the Department of Rocha, Uruguay, in winter and spring. The fresh green leaves were fed to 16 calves. Two calves that ingested the plant from Capao do Leao at 40 and 44 g/kg bw did not develop clinical signs. The other 14 calves had depression, abdominal pain, ruminal atony, ocular and nasal serous discharge, and dry feces with blood and mucus. Four calves developed icterus. First signs appeared 24-72 h after ingestion, and clinical period varied from 2 to 7 d. One animal had mild photosensitization. Calves dosed with 20 g/kg of plant from Santa Vitoria and 40 g/kg of plant from Uruguay had less severe clinical signs. All cattle recovered except 1 dosed with 40 g/kg of plant collected in winter in Santa Vitoria; it died 70 h after ingestion. Histologic lesions in the liver of this animal and in biopsies obtained 48 h after dosing other calves had centrilobular necrosis, sometimes extending to the midzonal region. Clinical signs and hepatic lesions were also observed in a calf dosed with 5 daily doses at 8 g/kg. Serum AST, GGT and bilirubin were increased. M laetum from Santa Vitoria was the most toxic for cattle, and the plant from Uruguay was the least toxic, suggesting variations in toxicity among plants from different regions.