Estimation of CH4 emissions from milk MIR spectra using respiration chamber as reference technique

Reducing the methane (CH4) from dairy cows is a challenging aspect of the cattle breeding. To permit large scale studies focusing on genetics and management, an equation has been developed to estimate individual CH4 emission from milk MIR spectra. The existing equation is based on values obtained with the SF6 technique. However, respiration chambers (RC) provide the gold standard for measuring CH4 production. Hence, the purpose of this work was to develop a new equation based only on data collected from RC to compare its statistical performance with the existing SF6 equation. Daily CH4 production data linked with milk MIR spectra have been collected from Switzerland (60 data – 30 cows), Germany (115 data – 26 cows), Denmark (132 data – 19 cows) and Northern Ireland (24 data – 12 cows) yielding a total of 331 RC measurements from 87 cows. Cows were fed with different diets types and were at variable lactation stages. Measured CH4 values ranged from 304 to 779 g/day (mean 504 g/ day). A fivefold cross-validation (CV) was performed to evaluate the robustness of the equation. The statistics of the equation based on RC measurements showed an R2cv of 0.62, a standard error of CV (SECV) of 60 g/day and a ratio performance deviation (RPD) of 1.6. In comparison, the equation based on 532 SF6 measurements (different countries and cows) showed R2cv of 0.70, SECV of 70 g/day and RPD of 1.8. Thus the SF6 equation appears to be more robust. It might be explained by the greater number of measurements, cows (165 vs 87), lactation number and stage and diet types. Thus, greater variability was included in the SF6 reference data set. Results obtained with the gold standard technique (RC) confirm the ability to estimate CH4 emissions from milk MIR spectra.