Accuracy of noninvasive breath methane measurements using Fourier transform infrared methods on individual cows

Individual methane (CH4) production was recorded repeatedly on 93 dairy cows during milking in an automatic milking system (AMS), with the aim of estimating individual cow differences in CH4 production. Methane and CO2 were measured with a portable air sampler and analyzer unit based on Fourier transform infrared (FTIR) detection. The cows were 50 Holsteins and 43 Jerseys from mixed parities and at all stages of lactation (mean = 156 d in milk). Breath was captured by the FTIR unit inlet nozzle, which was placed in front of the cow's head in each of the 2 AMS as an admixture to normal barn air. The FTIR unit was running continuously for 3 d in each of 2 AMS units, 1 with Holstein and another with Jersey cows. Air was analyzed every 20 s. From each visit of a cow to the AMS, CH4 and CO2 records were summarized into the mean, median, 75, and 90% quantiles. Furthermore, the ratio between CH4 and CO2 was used as a derived measure with the idea of using CO2 in breath as a tracer gas to quantify the production of methane. Methane production records were analyzed with a mixed model, containing cow as random effect. Fixed effects of milk yield and daily intake of the total mixed ration and concentrates were also estimated. The repeatability of the CH4-to-CO2 ratio was 0.39 for Holsteins and 0.34 for Jerseys. Both concentrate intake and total mixed ration intake were positively related to CH4 production, whereas milk production level was not correlated with CH4 production. In conclusion, the results from this study suggest that the CH4-to-CO2 ratio measured using the noninvasive method is an asset of the individual cow and may be useful in both management and genetic evaluations.