In a world of increasing complexity, politicians have only limited information about the relationship of policies and the outcomes. They often make use of simplified heuristics, i.e. policy beliefs. Hence, an influence opportunity for interest groups occurs: informational lobbying. It complements classic lobbying strategies, e.g. vote buying or campaign spending. Providing expert knowledge allows interest groups to influence legislators towards the preferred policy position. Aside from so-called "approved votes", German parliamentarians generally follow parliamentary group's discipline. Thus, experts' role within parliamentary groups is crucial. They deal with key issues and represent the parliamentary group in the committees. Furthermore, they work out the group's positions on these specific issues. They are the starting point for interest groups to disseminate their information and hence influence the legislators' positions. An exemplary field of complexity is the agricultural sector. In particular, livestock production is challenged by questions of sustainability, i.e. public expectations towards animal welfare, producers and consumers' welfare as well as ecological consequences. Importance of animal welfare is demonstrated by the ongoing debate about piglet castration or husbandry system standards. This raises two questions: First, to what extend are stakeholders able to gain direct access to politicians? Second, how can they use this structure to influence policy decisions? Using a social network approach, we first investigate the structure of three networks: exchange of expert knowledge, political support and informal social ties. In particular, we put emphasis on the connection between parliamentary actors and other stakeholders from society, i.e. interest groups. This refers to the first question. Second, we apply a model of political exchange using information and lobbying networks. Following Henning et al. (2019), this model not only includes political exchange, but also belief updating. Moreover, it considers direct as well as indirect ties. This analysis step serves to answer the second question.