Monensin and the Prevention of Tryptophan-Induced Acute Bovine Pulmonary Edema and Emphysema

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Abstract
3-Methylindole, a ruminal fermentation product of tryptophan, induces acute pulmonary edema and emphysema in cattle, and 3-methylindole is present in the ruminal fluid and blood of cows with a natually occurring form of this disease. Monensin, a polyether antibiotic and widely used feed additive for beef cattle, prevented tryptophan-induced acute bovine pulmonary edema and emphysema. Monensin acted by reducing the ruminal conversion of L-tryptophan to 3-methylindole both in vitro and in vivo. Lasalocid, also a polyether antibiotic, showed similar effects in vitro. These results provide a promising approach to prevention of this major respiratory disease of cattle.