Assessment of thoracic ultrasound as a diagnostic tool for lower respiratory tract disorders in sheep

Lower respiratory tract diseases (LRTDs) are a major cause of morbidity and mortality in sheep. Diagnosis is challenging not only because clinical signs are often mild or absent under field conditions, but also because adult sheep may develop a wide range of diseases affecting the lower airways with overlapping clinical presentations. This study evaluated the diagnostic performance of distance observation, comprehensive clinical examination, and thoracic ultrasonography (TUS) in sheep with suspected LRTDs, using post-mortem findings as the reference standard. A total of 103 sheep from different ages and production systems were examined following a standardised protocol including distance assessment, detailed respiratory examination, TUS, and complete necropsy with histopathology and pathogen detection. Distance observation identified very few clinically suspected animals and showed poor agreement with post-mortem diagnosis. Clinical examination detected 73 pulmonary lesions, mainly associated with the ovine respiratory complex (ORC), small ruminant lentiviral infection (SRLV), and gangrenous pneumonia (GP). TUS identified 72 lesions and showed high sensitivity for pulmonary consolidation, interstitial patterns, abscesses, cavitations, and subpleural abnormalities. Ultrasonographic patterns correlated closely with necropsy findings. Compared with distance assessment and clinical examination, TUS provided superior detection and characterisation of LRTDs. This study demonstrates the value of a standardized TUS-based approach for the ante-mortem differential diagnosis of the main ovine LRTDs and supports its incorporation as a rapid, reliable, and practical complementary diagnostic tool to improve clinical decision-making at flock level.