The most important message from the second set of models is that all models with cattle time varying infectivity (best fit) indicated higher values of infectivity after 31 st March than before (m = 0.73 (0.63, 0.83)) ( Table 2 ). This may seem paradoxical but reflects the fact that while culling (the effect of which is explicitly included in the input data) dramatically reduced case incidence in April, from May to September 2001, case incidence maintained itself at a low level -but almost entirely within cattle farms. This increase in cattle infectivity may therefore really reflect the impact of reduced biosecurity and/or increased non-compliance with movement controls.