PSXIV-4 Effects of various sampling condition on CH4 emission measurement by the CO2 method in Hanwoo steers.

Abstract The CO2 method (CO2T) is one of alternative methods for enteric methane (CH4) measurement in ruminants. We investigated effects of various sampling conditions (frequency and time of measurement, duration, number of sampling days, and with or without a mask to capture the breath) of the CO2T on CH4 emissions. Respiration chamber (RC) method was used as reference. Twelve Hanwoo steers with initial body weight of 338 kg and average age of 11.6 months were used. Diet consisted of 50% timothy hay and 50% concentrate, and 8 kg of diet was supplied twice daily in equal portions on an as-fed basis. Experimental period consisted of 21 d of premeasurement feeding, followed by 3 d of CH4 and CO2 measurement by the CO2T in the barn and then 3 d by the RC method. The CO2T was applied 3 times (early morning fasting, morning feeding, and afternoon feeding) per day for 3 consecutive days for 20 min with or without mask. During CO2T, CH4 and CO2 concentrations in exhaled breath were analyzed using gas analyzer and recorded every second for 20 min per animal. The CH4:CO2 ratio was calculated and multiplied by daily CO2 production to estimate daily CH4 emissions. Immediately after the CO2T, the RC method was applied, and CH4 emissions were calculated from the difference between inlet and outlet CH4 concentrations. Statistical analyses were performed using R version 4.0.4 software. Differences among sampling conditions were tested using one-way repeated measures ANOVA. Fisher’s LSD test with Bonferroni correction was used for post-hoc pairwise comparisons. Average CH4 emissions (L/day and L/kg dry matter intake) of two sampling times per day (the fasting and the morning feeding or the fasting and the afternoon feeding) by the CO2T did not differ (p >0.05) from those of the RC. CH4 emissions measured by the CO2T over 5 min differed (p< 0.05) from that of the RC, but those measured by the CO2T over 10, 15, or 20 min did not differ (p >0.05). There was no difference (p >0.05) between CH4 emissions measured by the CO2T on 1, 2, or 3 consecutive days and those measured by the RC. CH4 and CO2 concentrations (ppm) measured with mask were 7 and 8 times higher, respectively, than those measured without mask. There was no difference (p >0.05) between CH4 emissions measured by the CO2T with the mask and those measured without the mask. Thus, simple measurement of CH4 emissions twice a day over 10 min for 1 d without mask with the CO2T is sufficient to obtain similar results, comparable to the RC method. The CO2T is a viable alternative to the RC for measuring CH4 emissions, especially for on-site field measurements.