Cost of changing dairy cows' diet to reduce enteric methane emissions in livestock farms[Coût de la modification du régime alimentaire des vaches laitières permettant de réduire les émissions de méthane entérique dans les élevages]

Introducing fodder with high omega 3 content such as grass or linseed in the feed ration of dairy cows both improves the milk nutritional profile and reduces enteric methane emissions per litre. This lever is interesting to contribute to climate change mitigation but can also generate additional farm costs. Payment for Environmental Services, such as the Eco-Methane programme implemented by the association Bleu-Blanc-Coeur in France, can support a change of cows' diet in dairy farms through the valorisation of methane emissions reduction. The effectiveness of such a scheme depends on (i) the definition of a precise indicator of enteric methane emissions capturing the feeding effect, (ii) a payment level that would be sufficiently attractive to compensate for the additional costs faced by farmers. This study compares two indicators of enteric methane emissions to show the effect of taking feeding into account. It also assesses the extra cost of milk production if the grassland areas in fodder crop rotation systems were to be increased in French dairy farms. The estimation of a variable cost function based on data from the Farm Accountancy Data Network (FADN) suggests a significant increase of the marginal cost of milk production with additional hectares of grass in mountainous areas, and in plains farms for which maize silage represents less than 30% of the fodder crop rotation system.