"Eat less to gain more weight": an insufficient lever for achieving sustainable pigs

Pig farming is often criticised for its negative impacts, particularly greenhouse gas emissions, consumption of fossil resources and water pollution from nitrogen and phosphorus emissions. In Europe, the concentration of livestock farms in certain regions contributes to the eutrophication of coastal waters and groundwater, and in France, as elsewhere, reducing the environmental footprint of the pig industry has become a key objective. The industry is focusing in particular on reducing the consumption index, i.e. increasing the capacity of an animal to convert feed into meat, in order to reduce these impacts.

Indeed, feed production is responsible for the majority of the impacts of pig production in conventional systems. Until now, most studies have assessed impacts at the group level, assuming that all pigs consume the same type of feed adapted to an ‘average individual’. In reality, each animal has specific energy and amino acid requirements. This individual variability is often ignored, even though it has a significant influence on feed consumption, growth and waste.

A virtual farm based on real pigs

To take these differences into account, researchers at the Pegase joint research unit designed a model to simulate individual technical and environmental performance. Using data collected from 732 pigs, they created 732 virtual populations of 1,000 animals, each with the average performance of one of the 732 experimental pigs. The simulation model, based on InraPorc® software, was used to calculate the precise nutritional requirements of each of the 732 pigs and to simulate the composition of a feed best suited to their needs. The zootechnical, environmental and even economic (profitability) performance associated with this type of animal husbandry could then be simulated.

The impacts on climate change, fossil fuel use, soil acidification, water eutrophication potential and land use were assessed using life cycle analysis and expressed per kg of live weight at the farm gate.

This original, ‘individualised’ approach makes it possible to assess the environmental, technical and economic performance of each animal, taking into account its specific characteristics, such as its protein deposition potential or its amino acid requirements at the start of growth.

Three pig profiles and unexpected results 

   ‘Balanced’ pigs: efficient throughout the growth period, with moderate feed consumption and a feed composition that has a reduced environmental impact. These pigs perform best, both economically and environmentally.

   ‘Economical’ pigs: low nutritional requirements per kg of feed at the start of fattening and low-polluting feed, but slower growth than the other two profiles. Their lower efficiency leads to an increase in impacts per kg of meat, as they have a higher total feed consumption than the other profiles.

   ‘Demanding’ pigs: very efficient at growing quickly at the start of fattening, but their high amino acid requirements necessitate feed rich in soya or sunflower, which is more expensive and harmful to the planet.

Not all of the most efficient pigs (‘balanced’ and ‘demanding’) are necessarily suited to sustainable farming. Paradoxically, a fast-growing animal can generate more emissions because it requires feed that is very rich in vegetable protein, often imported, to achieve this growth. A sustainable pig is therefore a ‘balanced’ pig, efficient with stable growth potential throughout the fattening period. It is also a pig fed according to its actual needs, with feed adapted to both its metabolism and the environment. Adapting the diet to each individual could reduce nitrogen emissions and overall emissions.

This study shows that economic performance and environmental performance do not always coincide, but that it is possible to find a compromise by taking into account the diversity of animal profiles. The future of sustainable livestock farming will undoubtedly involve taking into account the economic and environmental performance of each animal, both in terms of selection and feed, in order to move from a yield-based approach to one that balances zootechnical, environmental and economic performance.