Indole toxicity in cattle.

Indole and 3-methylindole (3MI) are ruminal metabolites of L-tryptophan (TRP) and have similar physical and chemical properties. 3-Methylindole causes acute bovine pulmonary emphysema (ABPE). The effects of indole when administered orally to cows were determined. Four mature Holstein cows were given increasing doses of 0.05, 0.1 and 0.2 g indole per kg body-weight orally at two-week intervals. The animals were killed one week after the last dose. Plasma indole concentrations peaked three house after administration at 4.5, 8.8 and 19.8 microgram per ml after the 0.05, 0.1 and 0.2 doses, respectively. Detectable concentrations of indole (more than 0.02 microgram per ml) persisted in the plasma from three to 25 hours after dosing. Packed cell volume was decreased (P less than 0.01) at 48 and 72 hours after the 0.2 g per kg dose and at 72 hours after the 0.1 g per kg dose. Plasma haemoglobin was increased (P less than 0.05) at 48 hours after the 0.2 and 0.1 g per kg doses. By 72 hours after the 0.2 g per kg dose, all cows had mild diarrhoea and haemolysis and two of the cows had haemoglobinuria. At necropsy, microscopic lesions of haemoglobinuric nephrosis were seen in all four cows. No lesions of ABPE were found in any of the animals.