Supplementary files - Investigation of Bovine Viral Diarrhea Virus (BVDV)

BVDV is a productive and reproductive virus that causes a high global economic impact on dairy production systems. This research aimed to investigate the prevalence of BVDV at herd and individual levels in the most dairy-productive region in Brazil. The frequency of BVDV at the herd level was investigated by using RT-qPCR from bulk milk tanks monitored in 289 dairy farms between August 2020 and January 2022. Among these farms, 68 production systems were selected to investigate the prevalence of persistently infected (PI) animals by using 2 antigen-ELISA, in 21-day intervals, from ear-notches samples. A total of 2,902 RT-qPCR and 23,466 antigen ELISA were conducted. At the herd level, 23.87% (69/289) of dairy farms were considered infected, presenting at least one qPCR test positive. At the individual level, 41.17% (28/68) of a subgroup of selected farms had at least one animal positive in the antigen-ELISA test. Association between tests allows the classification of farms into four categories: level 0 - negative in both tests (41.17%; 28/68); level 1- RT-qPCR positive and Ag-ELISA negative (17.64%; 12/68); level 2- RT-qPCR negative and Ag-ELISA positive (13.23%; 9/68); level 3- positive for both tests (27.94%; 19/68). Multiple Correspondence Analysis (MCA) suggests a possible association between BVDV positivity with large-size farms, average daily milk production (herd), breed, and different somatic cell count levels. The confinement and intensification of animals from different categories, and the use of artificial bedding are associated with BVDV infection. Using waste milk or bulk tank milk is also a risk factor for the BVDV positive results in the RT-qPCR and antigen-ELISA. Despite the use of reproductive vaccines for most producers, the use of vaccines seems to be associated with farms positive for BVDV. This study presents the epidemiological frequencies of BVDV at the individual and herd level in the Campos Gerais paranaense region. This region ranks as the top milk-producing area in Brazil. In addition, the association of BVDV tests and farm characteristics indicates the farm risk for BVDV and guides specific control programs.