The study will involve approximately 500 dairy calves from 30 large-scale Estonian dairy farms. Each calf will undergo clinical examination and have blood samples taken to assess acute phase proteins and cytokines. Tracheobronchial lavage samples will be collected from both healthy and sick calves and analyzed for viruses and bacteria. Calves will be classified based on lung ultrasound and clinical data into various groups, including healthy, those with upper respiratory disease, subclinical pneumonia, and clinical pneumonia. The study aims to evaluate how well acute phase proteins and cytokines can differentiate between calves with lung lesions and healthy calves, and to characterize the lower respiratory tract virome in relation to lung consolidations, clinical disease, and systemic inflammation.