Ruminant Species Composition and Reported Methane Intensity in Global Milk Production: A 186-Country Decomposition Under Alternative Allocation Boundaries

Methane intensity of milk is often compared across ruminant species, but the Food and Agriculture Organization Corporate Statistical Database (FAOSTAT) identifies a dairy herd only for cattle; for buffalo, goats, sheep and camels it reports whole-herd methane. For 186 countries in 2020–2023 we allocated non-bovine herd methane to milk using country-specific shares of animals in milk. This reduced pooled intensity ratios to cattle from 2.9–17.9 to 1.1–5.2, and cattle had the lowest reported milk-allocated intensity in 53 of 107 multispecies countries (89 under whole-herd allocation). In the screened primary analysis (one implausible Mongolian sheep-milk series excluded), the world ratio decreased by 0.64 g CH4 kg−1; the three-factor decomposition attributed +0.48 g CH4 kg−1 to country shares, −0.10 to species mix and −1.02 to within-species intensity. With the series retained, the corresponding components were +0.57, −1.43 and +0.21. Cross-species comparisons are accounting constructs until boundaries and influential records are explicit.