Modelling cattle population as lifetime trajectories driven by management options: A way to better integrate beef and milk production in emissions assessment

Methods to assess the consequences of mitigation scenarios on greenhouse gas (GHG) emissions in the cattle sector have been widely developed. A crucial issue of these methods is handling the co-products in emissions allocation. In the cattle sector, milk and beef production systems are closely interconnected because of the meat obtained from dairy culled cows and fattened surplus calves. To fully evaluate a change in the dairy sector, the change in the meat production induced should also be taken into account. With this objective, a national cattle population model was developed, based on three sub-models. The herd functioning sub-model represents the bunch of cattle trajectories generated by reproductive and finishing processes depending on breeds, production levels and finishing types. Assuming a steady state herd, the demographics sub-model represents the number of animals in age groups depending on trajectories length. The production sub-model represents the number of animals slaughtered or exported, the quantity of carcasses, milk and direct GHG emissions. The model was calibrated on French data. The simulation of a reference scenario reflecting the French situation in 2010 confirmed that the model allowed linking cattle trajectories, demographics and production of milk, meat and direct GHG emissions. Scenarios for the dairy sector were simulated to illustrate the potential of such modelling approach to evaluate direct GHG emission at the national level. The results confirmed that the interconnection between dairy and beef sectors can modify the benefit of strategies such as dairy intensification. Further, the results also demonstrated that the compensation between beef and dairy cattle to achieve production objectives lead to a change in the type of carcass produced due to differences between breeds and finishing strategies. Accounting for such differences allows deepening the evaluation of the consequences of GHG mitigation options.