Protein nutrition and reduction of the carbon footprint of pig production: current state and perspectives

Abstract

Pig production is responsible for approximately 10% of greenhouse gases (GHG) emitted by all livestock in the world and strives to reduce its impacts. These GHG emissions are linked to feed production and manure management, contributing to 60% and 30% of farmgate emissions, respectively. Reducing dietary crude protein (CP) can lower emissions from both sources. The goal of this review was to summarize current knowledge on the impact of this strategy on GHG emissions related to differences in feed composition and the decrease in nitrogen emissions. Life cycle assessment (LCA) of feed production shows that the carbon footprint can be reduced by 8% for every 1-percentage-point decrease in dietary CP. This effect was obtained by reducing inclusion of feedstuffs with the highest impact (soybean meal & soy oil). However, these benefits depend strongly on the available and usable feedstuffs, the choice of environmental assessment databases and the economic context. Nitrogen emission modelling based on performance, updated recently by meta-analytical approaches, allows a complete assessment with farm-gate LCA. Decreasing GHG emissions by approximately 10% per kg of pig for a 1-percentage-point decrease in dietary CP was shown to be possible. Methodological and knowledge gaps remain to assess this strategy correctly: N₂O emission factors, taking into consideration the use of manure as a fertilizer, and better understanding of breakoff point in animal performance. Structural changes will also be a key to facilitate adoption of this practice, such as paying pig farmers for positive externalities.