Assay of fractions of bovine urine for carcinogenic activity after feeding bracken fern (Pteris aquilina).

Urine from cattle fed fresh and dried bracken fern for more than 2 years and urine from control cattle was extracted with ethyl acetate and divided into nonacidic and acidic fractions. The residue obtained after removal of the solvent was mixed with 4 times its weight of cholesterol, and the mixture was converted to pellets with the aid of a pellet press. Pellets containing these residues were surgically implanted into the bladders of mice, and one group of mice received pure cholesterol pellets. Five of 15 mice exposed to the acidic fraction and 1 of 13 mice exposed to the nonacidic fraction of the urine of cattle fed bracken fern developed carcinomas. One of 13 mice exposed to the acidic fraction and none of 11 mice exposed to the nonacidic fraction of urine of cattle not fed bracken fern developed carcinomas. When these results were analyzed by the exact method of 2 X 2 tables, the only group of animals with a tumor incidence which was significantly different from the control mice exposed to pure cholesterol (0 carcinomas in 11 animals) were the mice exposed to the acidic fraction of the urine of cattle fed bracken fern (P < 0.05). These preliminary results suggest that 1 or more car cinogenic substances occur in the urine of cattle ingesting bracken fern.