Comparison of enteric methane emissions between the respiration chamber and the carbon dioxide method in Holstein heifer.

The carbon dioxide (CO2) method (CO2T) for measuring enteric methane (CH4) emissions was validated using emissions data derived from respiration chambers (RC). The study was conducted over a period of 108 d using ten Holstein heifers with a mean initial body weight (BW) of 178 ± 24 kg and average age of 7 ± 0.7 months. There were three consecutive experimental periods, each consisting of 21 d of premeasurement feeding, followed by two 3-d periods of CH4 measurement sessions with the CO2T and the RC, respectively, for each animal. The diet consisted of 55% timothy hay and 45% concentrate, and was supplied twice daily at 1.2% to 1.5% BW on an as-fed basis. The CO2T measurements were conducted at morning and afternoon feeding. There were no significant differences in dry matter intake (DMI; P = 0.155), CH4 production (L/d and L/kg BW0.75; P = 0.492 and P = 0.625, respectively), and CH4 yield (L/kg DMI; P = 0.275) between the two methods. Results obtained using the RC and the CO2T were strongly correlated for both CH4 production (L/d; r = 0.67, P = 0.042) and CH4 yield (L/kg DMI; r = 0.61, P = 0.062). Linear regression analysis revealed moderate positive relationships between the two methods for CH4 production (R 2 = 0.52; P = 0.019) and CH4 yield (R 2 = 0.43; P = 0.039). In conclusion, the CO2T and the RC produce comparable results, with acceptable accuracy and precision.