Abstract
The carbon dioxide (CO(2)) method (CO(2)T) for measuring enteric methane (CH(4)) 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 CH(4) measurement sessions with the CO(2)T 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 CO(2)T measurements were conducted at morning and afternoon feeding. There were no significant differences in dry matter intake (DMI; P = 0.155), CH(4) production (L/d and L/kg BW(0.75); P = 0.492 and P = 0.625, respectively), and CH(4) yield (L/kg DMI; P = 0.275) between the two methods. Results obtained using the RC and the CO(2)T were strongly correlated for both CH(4) production (L/d; r = 0.67, P = 0.042) and CH(4) yield (L/kg DMI; r = 0.61, P = 0.062). Linear regression analysis revealed moderate positive relationships between the two methods for CH(4) production (R (2) = 0.52; P = 0.019) and CH(4) yield (R (2) = 0.43; P = 0.039). In conclusion, the CO(2)T and the RC produce comparable results, with acceptable accuracy and precision.