There is an ongoing debate in The Netherlands between farmer organisations, conservationists and government about whether the health status of feral animals jeopardises the health status of domestic cattle. In this respect, BHV1 is the most prominent acute problem. Although the compulsory eradication programme for BHV1 in domestic cattle populations is suspended, eradication of BHV1 still takes place on a voluntary basis.The objective of this thesis was to study the role of Heck cattle andred deerliving in Dutch nature reserves for the possible introduction of BHV1 in domestic cattle. Therefore, the research question whether BHV1 could persist in Heck cattle andred deerpopulations had to be answered.The persistence of BHV1 in small cattle populations was studied by estimating the mean time to extinction using a stochastic model. For realistic parameter values, it was found that the mean time to extinction was already in the order of 100 years in a population of 10 animals. As the contact structure of the Heck cattle populations may influence BHV1 transmission and thus also BHV1 persistence, this contact structure was quantified using behaviour observations. It was shown that the contact structure was more limited for transmission of BHV1 in the autumn and winter-spring period than in the summer period. During summer most transmission would take place based on the number of contacts. The effect of vaccination was then studied on the dynamics and persistence of BHV1 in the Heck cattle populations. Serological data of BHV1 in the Heck cattle populations were combined with model simulations. From the serological data and simulations results it was clear that vaccination of a large part of the Heck cattle population decreased the seroprevalence for BHV1. It was also found that in 3 out of 20 simulated populations, BHV1 became already extinct within 15 years for the partly vaccinated populations. For thered deerpopulations it was quantified to what extent BHV1 might spread amongred deerusing two transmission ...