This experiment was design to address the following points in relation to the acute poisoning by bracken fern (Pteridium aquilinum) in cattle: 1) the severity of the thrombocytopenia in different stages of the intoxication and its relationship to possible deficits in the secondary hemostasis, 2) the relationship between neutropenia and the morphological signs of septicemia occasionally found at necropsy, and 3) the mechanism of anemia and its relationship with blood loss, medium life of erythrocytes and the progress of the disease. The fresh green upper parts of P. aquilinum were fed to four mixed breed calves with average age of 18 months and weights ranging from 190 to 215 kg. A calf of similar age and weight was kept together with the other four under the same conditions, except for the ingestion of P. aquilinum. The four fern-fed calves died with typical features of acute bracken fern poisoning after being fed with the plant for 53-58 days daily doses of 8.0, 8.6, 10.2, and 10.6g/kg body weight totaling at the end of the experiment, respectively, 59.3%, 63.3%, 47.4%, and 47.5% of bracken fern in relation to their body weight. The disease was characterized by fever up to 42.5°C and varying degrees of hemorrhages observed clinically, at necropsy and on histological examination. Death occurred 6-7 days after the onset of fever. The hematological changes consisted mainly of marked thrombocytopenia and neutropenia. Two of the four affected calves had mild anemia. The deficits in secondary hemostasis were mild in each case. There were no significant changes thus permitting to rule out the role of secondary hemostasis in the pathogenesis of the hemorrhages in the bracken fern poisoning. The measurement of fibrin degradation products in the serum showed conflicting results and did no allow for a solid conclusion regarding the role of disseminated intravascular coagulation in the pathogenesis of the hemorrhages in fern poisoning. The cytology and the histopathology of bone marrow from the four poisoned calves revealed marked decrease in the numbers of hematopoietic cells from the three marrow lineages, which characterizes marrow failure due to aplasia; it was concluded that the events of the primary hemostasis due to thrombocytopenia are responsible for the hemorrhages. In blood culture from three affected calves there was growth of Klebsiella oxytoca, Staphylococcus hyicus and Staphylococcus aureus, indicating that septicemia, facilitated by neutropenia could have a role in the death of cattle acutely poisoned due to the ingestion of P. aquilinum. Additional points of the interest in the acute experimental poisoning by bracken fern in cattle reported here were the development of hematuria and the so called laryngeal form.
Diseases of cattle; poisonous plants; bracken fern; Pteridium aquilinum; disturbs of hemostasis; bone marrow aplasia; pathology
