The chronic toxicity of bracken fern (Pteris aquilina) harvested near Bolu, Turkey, where bovine bladder tumors occur in a high incidence, was tested by feeding the plant to 18 cows of native stock ranging from 1.5 to 4 years of age. The cows weighed from 100 to 150 kg and were fed from 300 to 600 gm of dried or 400 to 1000 gm of fresh plant daily in an attempt to simulate natural exposure in the field. Of 18 animals fed bracken fern, 10 developed neoplasms of the urinary bladder and 3 of these lesions were carcinomas. The 2 carcinomas which invaded the muscular wall of the urinary bladder were found 2.6 and 3.3 years after the initiation of feeding. The 8 animals which died of toxicity without evidence of bladder neoplasms after a mean feeding time of 163 days included 5 of the 7 animals fed the highest dosage of bracken. Most of the animals which developed bladder lesions were fed bracken at a lower dietary level for a mean period of 550 days (range, 276 to 1192 days). Ten control animals not exposed to bracken fern did not manifest any clinical symptoms during the experiment. The histologic appearance of the neoplasms and other parameters of the study suggest that this experiment has resulted in the production of lesions that are indistinguishable from the naturally occurring bovine bladder tumors which are a common feature of bovine enzootic hematuria. These results provide further evidence for the presence of a carcinogenic substance in bracken fern.

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This investigation was supported by Grant FG-TU-102 of the United States Department of Agriculture, Agricultural Research Service, and by USPHS Research Grant No. CA-08254 from the National Cancer Institute.

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