Network analysis of the German cattle trade net - Preliminary results

In this paper data on the movement of animals between farms of a specific county in Germany during January 1(st) 2004 and June 30(th) 2006, which are recorded in the HI-Tier database, is investigated exemplarily. Network analysis tools are used for the investigation. A network consists of nodes and connections (edges) between the nodes. In case of animal movement to and from farms, the farms represent the nodes and the movements between the farms represent the edges. An edge always connects two nodes. Concerning the spread of diseases between farms, usually the geographical closeness between farms is brought into focus (distance dependent spread). But, because animals may be traded on large distances, a farm is able to infect other farms in an arbitrarily far distance (distance independent spread). For the description and the analysis of networks, the geographical location of the nodes is irrelevant. In order to assess the relevance of farms with respect to the spread of a disease on a network it is convenient to calculate measures of centrality. In degree and out degree are the simplest measures of centrality. In degree and out degree simply count the number of connections to and from a specific farm to other farms respectively. The degree distribution supplies relevant information about the structure of a network and also about the dynamics of a disease spreading on the network. Additional centrality measures are the Betweenness and the Closeness of a farm. The Betweenness indicates the frequency of a farm lying on the shortest path between other farms of the network. The Closeness of a farm indicates the accessibility of other farms from this farm