Modelling the dynamics of the health-production complex in livestock herds: a review

This paper reviews how the dynamics of the health-production complex in livestock herds is mimicked by livestock herd simulation models. Twelve models simulating the dynamics of dairy, beef, sheep and sow herds were examined. All models basically included options to alter input and output of reproductive animals in a manner which could be related to health problems. Direct effects of diseases on growth or milk production were, however, addressed in only a few models and were confined to a few basic relations if modelled.

The lack of effects on individual animal production in the models may relate to difficulties in obtaining valid parameters for these effects. We recommend: (1) that disease-production relations be based on mechanistic, reasonable hypotheses at the animal level; or (2) that groups of animals be specified that have different disease-production relations. These relations and their interactions could be studied by applying the same standards of analysis to simulated data as to real herd data.