Association of 3-methyleneindolenine, a toxic metabolite of 3-methylindole, with acute interstitial pneumonia in feedlot cattle

Objective-To compare concentrations of 3-methyleneindolenine (3MEIN) in lun g tissues obtained from feedlot cattle that died as a result of acute Inter stitial pneumonia (AIP) and cattle that died as a result of other causes an d to compare blood concentrations of 3MEIN in healthy feedlot cattle and fe edlot cattle with AIP. Study Population-Blood samples and lung tissues collected from 186 cattle h oused in 14 feedlots In the western United States. Procedure-Samples of lung tissues were collected during routine postmortem examination and submitted for histologic, microbiologic, and toxicologic ex amination. Blood samples were collected from cattle with clinical manifesta tions of AIP and healthy penmates. Histologic diagnoses were categorized as AIP bronchopneumonia (BP), control samples, and other disorders. Concentra tions of 3MEIN were determined in lung tissues and blood samples, using an ELISA. Results-Concentrations of 3MEIN in lung tissues were significantly greater in AIP and BP samples, compared with control samples. Absorbance per microg ram of protein did not differ between BP and AIP samples. Blood concentrati ons of 3MEIN were significantly greater in cattle with AIP compared with he althy cattle or cattle with BP Odds of an animal with AIP being a heifer wa s 3.1 times greater than the odds of that animal being a steer. Conclusions and Clinical Relevance-Increased pulmonary production of 3MEIN may be an important etiologic factor in feedlot-associated AIP.