A mechanistic model captures livestock trading, disease dynamics, and compensatory behaviour in response to control measures

Martin A. Knight, Michael R.Hutchings, Piran C.L. White, Ross S. Davidson, Glenn Marion*

• Model of trade dynamics via behaviour that maintains farm-level animal flow.

• This results in compensatory behaviours that undermine disease control.

• Efficient control must balance such system dynamics and burden of trade disruption.

• Post-movement testing disrupts trade but can be effective in controlling disease.

• Methods show how to model behavioural responses in dynamic transmission networks.

Trade is a complex, multi-faceted process that can contribute to the spread and persistence of disease. We here develop novel mechanistic models of supply. Our model is framed within a livestock trading system, where farms form and end trade partnerships with rates dependent on current demand, with these trade partnerships facilitating trade between partners. With these time-varying, stock dependent partnership and trade dynamics, our trading model goes beyond current state of the art modelling approaches. By studying instantaneous shocks to farm-level supply and demand we show that behavioural responses of farms lead to trading systems that are highly resistant to shocks with only temporary disturbances to trade observed. Individual adaptation in response to permanent alterations to trading propensities, such that animal flows are maintained, illustrates the ability for farms to find new avenues of trade, minimising disruptions imposed by such alterations to trade that common modelling approaches cannot adequately capture. In the context of endemic disease control, we show that these adaptations hinder the potential beneficial reductions in prevalence such changes to trading propensities have previously been shown to confer. Assessing the impact of a common disease control measure, post-movement batch testing, highlights the ability for our model to measure the stress on multiple components of trade imposed by such control measures and also highlights the temporary and, in some cases, the permanent disturbances to trade that post-movement testing has on the trading system.

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