Pneumonia is the most prevalent disease in Swedish feedlot cattle herds, causing mortality as well as affecting weight gain, rearing time and economy. Viral infections, including bovine respiratory syncytial virus (BRSV) and bovine coronavirus (BCV) as major actors, cause respiratory disease. Treatment of many calves with antibiotics for secondary bacterial pneumonia conveys a risk to develop resistance to antibiotics. We are convinced that recruitment of calves purely from BRSV/BCV-free dairy herds would increase calf health dramatically. Today calves are often mingled from various herds and run a high risk of disease. The studies are conducted in commercial feedlot herds during three years, assessing prevalence of infections, weight gain, disease incidence, motrality, treatments and abattoir registrations. Herds introducing calves only from BRSV/BCV-free dairy herds will be compared with conventionally mixed calf groups and health effects evaluated economically.