Relationships between methane emissions and technico-economic data from commercial dairy herds

Considering economic and environmental issues is important for the sustainability of dairy farms. Regarding environment, direct methane (CH4) emissions from cows are of increasing concern. Many studies examined CH4 variation factors but often on a low number of experimental cows. Also, few studies linked CH4 to economic aspects of dairy farms. The innovative aim of this study was to highlight technical factors associated with dairy cow CH4 emissions and gain insight into the relationships between CH4 and herd economic results by the use of large scale and on-farm data. A total of 525,697 individual CH4 predictions from milk mid-infrared (MIR) spectra [MIR-CH4 (g/day)] of milk samples collected on 206 farms during the Walloon milk recording were used to create a CH4 proxy at the herd by year (herd*year) level. This proxy was merged with accounting data. This allowed a simultaneous study of CH4 emissions and 56 technico-economic variables for 1,024 herd*year records from 2007 to 2014. Significant effects were detected from ANOVA analyses and correlations (r). MIR-CH4 was weakly linked to technical variables considered individually (r < 0.38), suggesting complex associations between variables. Lower MIR-CH4 was associated with lower fat and protein corrected milk (FPCM) yield (r=0.18), lower milk fat and protein content (r=0.38 and 0.33, respectively), lower quantity of milk produced from forages (r=0.12) and suboptimal reproduction and health performances (e.g. higher calving interval (r=-0.21), higher culling rate (r=-0.15)). On an economic point of view, lower MIR-CH4 was associated with lower gross margin per cow (r=0.19) and per litre FPCM (r=0.09). To conclude, this study suggested that low dairy cow CH4 emissions tended to be associated with suboptimal and also less profitable herd management practices. Further research is needed to confirm and expand on these results.