BRSV seroprevalence and associated risk factors on Dutch dairy farms

Bovine respiratory syncytial virus (BRSV) causes infections of the respiratory tract of cattle and is endemic in the Netherlands. We aimed to update our knowledge on the seroprevalence of BRSV in youngstock on Dutch dairy farms by performing a cross sectional study during the winter of 2021-2022 and a telephone survey with the farmers to map the most important risk factors for the introduction, presence, and circulation of BRSV. Of 671 sampled calves among 135 herds, we found a seropositivity of 75 % at calf level and 77 % on herd level. Risk factors appeared similar to those identified by others including a higher ratio of youngstock versus adult cows and suboptimal colostrum administration. We concluded that the BRSV seroprevalence at animal and herd level is still substantially high, confirming the endemic circulation of this virus on the majority of the Dutch dairy farms. But given that there is also a smaller number of seronegative herds and the available knowledge about biological sound risk factors for BRSV circulation, it could be worth investigating the feasibility of decreasing the seroprevalence of BRSV at herd level in the Netherlands taking into account the lessons learned from the Norwegian control program.