The objective of this study is to simulate a payment for environmental services scheme to reduce enteric methane emissions per litre of milk by incentivizing farmers to modify the diet of dairy cows. We estimated a milk yield function by distinguishing between types of fodder and concentrate feeds. Methane emissions were calculated from the technical relationship between different feed sources and milk productivity. The heterogeneity of the production conditions faced by the farmers was identified from a mixture model estimated by the EM algorithm. The results show that, with the introduction of the payment for environmental services, farmers reduce their methane emissions per litre of milk the more their production conditions, as reflected by the quality of their forage, are good.