Prediction of nutrient flows with potential impacts on the environment in a rabbit farm: a modelling approach

To face the increasing demand for animal products throughout the world, livestock-farming systems have been intensified. This intensification has proven to be economically effective but is noted for its negative impact on the environment through the production of ammonia (NH3) and the greenhouse gases nitrous oxide (N2O) and methane. In this context, dynamic models are useful tools to evaluate the effects of farming practice on nutrient flows and losses to the environment. This paper presents the development of a model simulating the flows of nitrogen (N) and phosphorus (P) in a rabbit production farm. The model is comprised of two submodels. The first submodel simulates the number of animals in the farm (births, deaths, culling of does/fatteners) and their respective performances (growth, feed intake, milk production). The second one simulates the excretion of N and P for each animal category using a mass-balance approach between intake (feed and/or milk intake) and exports (body deposition, milk production, gestation). Specific emission factors are then applied to the excreted N amounts to estimate total N, NH3 and N2O losses in the housing unit and during manure storage. Methane emissions from enteric fermentations and manure are also estimated. A simulation example based on French technicoeconomic data illustrates how the model could be used to study the dynamics of animal populations within the system and of nutrient flows. Finally, there is a need for new knowledge (experimental data) to improve the model and help design more sustainable rabbit production systems by identifying best practices that minimise environmental impacts