Genetic selection: a lever for sheep farming with less environmental impact

The Paris agreements commit more than 50 signatory countries to reducing their GHG emissions in order to limit global warming to 1.5°C by the end of the 21st century. Livestock farming contributes around 15% of global GHG emissions, mainly due to the methane-generating digestive process of ruminants. This enteric fermentation of plant fibers is responsible for 90% of GHG emissions from livestock farming.

Sheep farming, with almost 1.2 billion animals worldwide, contributes 6% of total enteric methane emissions, and must therefore implement strategies to reduce its emissions, including genetic selection. The GrassToGas European project has brought together a consortium of 7 partners* to study GHG emissions and feed efficiency, and to propose strategies for using these two traits in breeding to limit the environmental footprint of livestock farming.

The benefits of genomic selection

During the project, several thousand animals were phenotyped for feed intake, feed efficiency and/or GHG emissions. Based on the various measurement protocols, the scientists drafted recommendations that were forwarded to ICAR (International Committee for Animal Recording) to encourage internationally harmonized phenotyping. However, routine phenotyping of these traits, particularly feed intake, remains costly and therefore difficult to envisage. To overcome these costs, scientists have shown that it is possible to predict feed intake levels from zootechnical data with satisfactory accuracy. However, predictions of feed efficiency and GHG emissions are still not very accurate. This reinforces the importance of implementing genomic selection for these traits, which are rarely routinely recorded.

Modelling work on British sheep systems has estimated that taking methane emissions into account in selection objectives would enable a 2.5 to 7% annual reduction in these emissions by suckling sheep. As for French research, it has shown that selecting for feed efficiency in young growing animals can also produce adult animals (males and females) that are more efficient when ingesting forage. Additional results tend to show a disadvantageous genetic relationship between feed efficiency and methane emissions.

In conclusion, more phenotypic measurements and data collected at the level of farming systems will help to clarify the links between GHG emissions and feed efficiency, which remain contradictory between studies, including those carried out in the GrassToGas project.