The potential of milk fatty acids as biomarkers for methane emissions in dairy cows: a quantitative multi-study survey of literature data

SUMMARY Relationships between milk fatty acids (MFA) and methane (CH 4 ) emissions from dairy cattle were explored. Data from a total of 12 studies including 39 treatments were gathered in the database. Methane was expressed as daily emissions (g/d), relative to dry matter intake (g/kg), milk production (g/kg milk) and body weight (g/kg). The univariate correlations between MFA and CH 4 were based on absolute means and on relative changes of each treatment compared with its corresponding control. Saturated fatty acids, odd- and branched-chain FA and long-chain poly-unsaturated FA were positively related to CH 4 , while cis - and trans- isomers of mono-unsaturated FA were negatively related to CH 4 . However, most of the coefficients of determination ( R 2 ) of these univariate regressions ranged from 0·2 to 0·7, indicating that individual MFA only explain a limited part of the variation in CH 4 . Significant relationships between MFA and CH 4 varied depending on the unit in which emissions were expressed. Similarly, some MFA seemed more suited to predict relative changes in CH 4 emissions rather than absolute amounts. The present findings contribute to the exploration of the potential of MFA as biomarkers for CH 4 emissions from dairy cattle, although differences between studies in the detail of MFA analysis and hence the number of MFA reported in the current study, complicates this kind of literature survey.