Environmental and economic assessments of selection for feed efficiency in pigs

The aim of this thesis was to develop an approach to evaluate breeding strategies for feed efficiency in pigs to identify mitigating solutions for environment and economy. A life cycle environmental assessment model (LCA) and a bio-economic model were developed at the individual level. It enabled to assess varieties of feed efficiency scenarios on an individual basis. The models were applied to assess the impacts of selection for feed efficiency alone or combined with diet optimisation as a strategy to achieve overall farm feed efficiency. Data from two pig lines selected for feed efficiency based on residual feed intake (RFI), showing genetically contrasted feed efficiency, were used. A multiple objective diet optimisation was developed using genetic line nutritional requirements as constraints, and minimising a score combining environmental impacts and/or cost. The consistency of the models was obtained from considering net energy as the core linkage between line requirements, ingredients dietary composition, price, and environmental impacts. The individual performance traits in response to new optimised diets for each line were simulated with the InraPorc® pig growth simulation software. For a least cost, a least environmental impacts, and a joint economic-environment diets, these performances were used as inputs to the LCA and bio-economic models. The individual economic and environment assessments showed that selection for improved feed efficiency in pigs increases the profitability by 23.4% and reduces the environmental footprint by 7%. Selection for feed efficiency combined with diet optimisation even enhanced these economic and environmental improvements through restoring part of the advantages of selection that did not emerge due to feeding the lines the same diet. Thus, for increased pig sustainability, a selection for feed efficiency should be combined to diet optimisation including environmental constraints. However, feeding less efficient pigs an optimised diet strongly reduced the genetic differences and alleviated most of the economic and environmental burdens. Finally, the assessment at the individual level gave access to the covariances between the performance traits and the environmental impacts and profit. High correlations of feed conversion ratio with environmental impacts and profit in both lines confirmed the importance of feed efficiency as a lever for the sustainability of pig production, and the moderate correlations with RFI pointed this trait as a potential lever to improve environmental impacts with limited correlated effects on other production traits. These results and tools will contribute to move from breeding goals essentially based on economic objectives to more holistic breeding goals, to contribute to increased sustainability in pig production