PSXI-17 Comparison of enteric methane production between the respiration chamber and the CO2 method in Holstein heifers

Abstract The objective of this study was to validate the carbon dioxide (CO2) method (CO2T) in comparison with the respiration chamber (RC) method for the measurement of enteric methane (CH4) emission. The study was conducted over 108 d with Holstein heifers [n = 10; initial body weight (BW) = 178 kg; and age, 7.7 mo). The study consisted of 3 consecutive measurement periods and each period consisted of 21 d of feed adaptation followed by 15 d of CH4 measurement using the CO2T (3 d) and the RC method (12 d). The 55% timothy hay and 45% concentrate were fed twice daily at 1.2% to 1.5% of BW on an as-fed basis. The CO2T was used for 3 d during the morning and afternoon feeding. For the CO2T, CH4 and CO2 concentrations of exhaled breath from each animal were continuously analyzed by gas analyzers and recorded every 10 sec for 10 min per animal. The CH4:CO2 ratio of the data were calculated and multiplied by daily CO2 production of each animal to determine daily CH4 production. Right after the CO2T measurement, CH4 emission was measured using the RC method by the difference between the inlet and outlet CH4 concentration of the RC. Statistical analyses were performed using the software R version 4.0.4. Differences in dry matter intake (DMI), CH4 production, and CH4 yield between the two methods were tested using the Wilcoxon signed-rank test. DMI was not different between the RC method and the CO2T measurements. The CH4 production (L/d, L/kg BW0.75) and yield (L/kg DMI) determined by two methods were similar (127 vs 120 L/d, 2.05 vs 2.16 L/kg BW0.75, and 23.5 vs 21.6 L/kg DMI for RC vs CO2T, respectively). There was a positive relationship between DMI (kg/d) and CH4 production (L/d) for both of the RC method (R2 = 0.46, P < 0.05) and the CO2T (R2 = 0.72, P < 0.01). Linear regression analysis of CH4 production (L/d) between the RC method and the CO2T showed a moderate positive relationship (R2 = 0.52, P < 0.05). Pearson correlation analyses showed a strong relationship between the RC method and the CO2T for CH4 production (L/d; R2 = 0.72, P < 0.05). In conclusion, the CH4 production of Holstein heifers estimated by the CO2T did not differ from that measured by the RC method, and method agreement indices showed moderate positive correlations. The CO2 method could be used as one of the alternative CH4 measurement techniques comparable to the respiration chamber method.