Antibody tracing, risk factors and seroepidemiology of bovine respiratory syncytial virus and bovine adenovirus-3 were investigated in 22 Industrial and Semi-Industrial dairy Holstein farms. Serum samples (n=736) from various ages of unvaccinated cows were collected from May to September 2012. Risk factors including age, past history of respiratory diseases, amount of milk production, husbandry type and herd size were considered. Data were analyzed by Chi-square and logistic regression. Results indicated that the infection with some of individual viruses was related to past history of respiratory disease and herd size. No specific pattern was seen on the effect of level of milk production on seropositivity of animals. The seroprevalence for BRSV and BAV-3 were 89.1% and 88%, respectively. The present study indicates that infections of bovine respiratory viruses frequently occur in cattle of Fars province and the main viral cause of primary occurrence of respiratory diseases may be due to aforementioned viruses.