The aim of this study is to reveal infection dynamics of bovine respiratory syncytial virus (BRSV), bovine parainfluenza virus type 3 (PI-3), bovine herpesvirus 1 (BHV-1), bovine viral diarrhea virus (BVDV), bovine adenovirus type 3 (BAV-3) and bovine coronavirus (BCoV), which are important viral pathogens of respiratory disease complex in ruminants. Through such an analysis, the regression period of maternally derived antibodies and optimum vaccination time in calves can be recommended. A total of 10 farms were grouped as large (4)-, medium (2)- and small (4)- sized enterprises according to their animal population. Newborn calves (n: 94) delivered during a calendar month on the farms were studied. Blood samples were collected from these calves during their 1st, 2nd, 3rd, 4th, 6th, 8th, 10th and 12th months of age. Blood samples were also taken from their dams during the first sampling. Neutralizing antibody titers were detected using the serum neutralization test (SN50). New PI-3 and BVDV infections at the early stages of life were determined in the calves. Maternal antibodies began to decrease in the 2nd month for BRSV, BHV-1 and BAV-3 (97.8%, 25.5% and 91.4%) and in the 3rd month for PI-3, BVDV and BCoV (85.1%, 67% and 93.6%). It was concluded that maternal antibodies begin to decrease after the 1st month and that the possible first exposure of calves to respiratory viruses is after the 2nd month. Therefore, it is recommended that the first vaccination program including prime and booster doses can be applied between 2 and 4 months of age. Furthermore, re-vaccination of animals at 6 months after the booster dose is also suggested. (C) 2015 Elsevier B.V. All rights reserved.