Farm status and animal movement matrix between study Farms 1–42 (2005–2010): Each coloured node represents an individual farm. Farm number is stated alongside the node. The status of each farm is defined by the colour of its node such that: a “Black Node” represents a farm of unknown status, a “Green Node” represents a BVDV free farm, a “Red Node” represents a BVDV infected farm and a “Yellow Node” represents a farm that is currently eradicating BVDV. Numbers of animal movements are indicated alongside the arrow that illustrating the direction of movement. The arrow line width is proportional to the number of movements. Geographic position and relationships are not represented in the figure.