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Reduction of 3-Methylindole Production and Prevention of Acute Bovine Pulmonary Edema and Emphysema with Lasalocid^1,2,

Washington State University, Pullman 99164-6320

Abstract

A study was conducted to determine the dose of lasalocid that would effectively reduce ruminal conversion of tryptophan (TRP) to 3-methylindole (3MI) and prevent the development of acute bovine pulmonary edema and emphysema (ABPE). After adaptation to a maintenance diet for 3 wk, 20 mature beef cows were randomly divided into four groups of five cows each and fed 0, 200, 400 or 600 mg lasalocid·head^–1·d^–1 in .5 kg ground barley for the 12-d experimental period. In vitro conversion of TRP to 3MI and indole by ruminal fluid and volatile fatty acid (VFA) concentrations were determined on d 0, 2, 4, 6 and 12. On d 6, an oral dose of .35 g TRP/kg body weight was given to induce ABPE, and ruminal production of 3MI and indole was determined at intervals thereafter. Formation of 3MI was sharply reduced (P<.01) both in vitro and in vivo by lasalocid treatment at 200 mg·head^–1·d^–1 Further suppression of 3MI production occurred as the lasalocid dose was increased (P<.05). Linear (P<.0001) and quadratic (P<.002) components were determined for the relationship between lasalocid dose and 3MI production. Indole formation was variable, but tended to increase (P<.05) with increasing lasalocid dose. Cows that received no lasalocid developed moderate to severe clinical signs of ABPE and three cows died of acute lung disease. Lasalocid treatment at all levels prevented ABPE. Lasalocid decreased ruminal acetate and butyrate, and increased propionate concentration (P<.01). Total VFA concentration was increased (P<.05) in cows given 600 mg lasalocid·head^–1·d^–1 These results demonstrate that 200 mg lasalocid·head^–1·d^–1 inhibited 3MI formation sufficiently to prevent the onset of ABPE.

¹ Scientific Paper No. 6759. Agricultural Research Center, Washington State Univ., Pullman. Projects 1893 and 0399.

² Supported in part by NIH grant HL-13645 and a grant from Hoffman-LaRoche, Inc., Nutley, NJ 07110.

³ Dept. of Anim. Sci.

⁴ Dept. of Vet. Microbiol. Pathol.

⁵ The technical assistance of Karen Weller is gratefully acknowledged.