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

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 BW^0.75; 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.