Toxic interstitial lung disease in cattle

Interstitial lung disease refers to lesions involving primarily any of the 3 layers of the alveolar wall (endothelium, basement membrane, alveolar epithelium) and the contiguous bronchiolar interstitium. Toxic agents are a significant cause of interstitial lung disease in cattle, primarily interstitial pneumonia. We review the most important substances associated with interstitial lung disease in cattle, addressing their epidemiology, clinical signs, pathogenesis, and lesions. These include the amino acid L-tryptophan (ingested with lush green forages), the toxin 4-ipomeanol (produced by moldy sweet potatoes infected with <i>Fusarium solani</i>), toxic plants such as <i>Perilla frutescens</i> and <i>Zieria arborescens</i>, and nitrogen dioxide (NO₂) released from recently filled silos. The diagnosis of these disorders may be challenging because the clinical signs and lung lesions often overlap regardless of the cause. Thus, a definitive diagnosis typically relies on a thorough epidemiologic investigation and confirmation of exposure of affected cattle to the potential cause. Laboratory confirmation of specific toxins is often limited because many are rapidly metabolized and unstable after ingestion, making their detection difficult.