The fattening unit model is a discrete-event mechanistic model with stochastic biological traits (pig feed intake, growth potential and risk of mortality) and a one-day time step. The pig fattening system is composed of pig herd, farm management and farm infrastructure. The pig herd is divided into successive batches of pigs of the same age which are reared in the same room from the beginning of the fattening period until shipping to the slaughterhouse. Each pig is represented using an individual-based model adapted from the InraPorc model (van Milgen et al., 2008). The InraPorc model simulates feed intake, body protein and lipid depositions, and the resulting growth and nutrient excretion of each pig. Each pig is attributed a profile which includes an initial body weight (BW70), the mean protein deposition (PDm), a shape parameter of the protein deposition function (BGompertz), and two parameters describing its feed intake (a, b), set to generate the appropriate structure of a pig herd according to Vautier et al. (2013). Farm management is represented by farmer’s practices and a calendar of events containing tasks to perform. At each time step of the simulation, the events corresponding to the current day are read in the calendar and processed. The practices include batch management, allocation of pigs to pens, feeding practices and slaughter shipping practices. Farm infrastructure is represented by a number of fattening rooms, each with a number of pens of a given size, which are provided as input parameters to the model. A buffer room can be used at the end of the fattening period to extend the fattening period of the lightest pigs which have not reached the minimum slaughter weight without economic penalties. Once the last pigs of a batch are moved to the slaughterhouse or to a buffer room, the fattening room is considered empty after a disinfection period and ready for a new batch. The model calculates technical, economic and environmental results for each fattening pig and globally for the unit. Environmental impacts of each slaughtered pig are estimated using LCA, taking into account impacts from the extraction of raw materials to the farm gate. More detailed description of the model and the LCA performed by the model can be found in Cadero et al. (2017).

This study was supported by CIFRE Ph.D. funding (agreement in industry for training by research) of the ANRT (National Agency for Research and Technology) with co-funding from the call for projects "Targeted research and innovation" of the French Ministry of Agriculture, Agrifood, and Forestry.