The objective of this study was to compare the precision of CH4 estimates using calculated CO2 (HP) by the CO2 method (CO2T) and measured CO2 in the respiration chamber (CO2R). The CO2R and CO2T study was conducted as a 3 × 3 Latin square design where 3 Dexter heifers were allocated to metabolic cages for 3 periods. Each period consisted of 2 weeks of adaptation followed by 1 week of measurement with the CO2R and CO2T. The average body weight of the heifer was 226 ± 11 kg (means ± SD). They were fed a total mixed ration, twice daily, with 1 of 3 supplements: wheat (W), molasses (M), or molasses mixed with sodium bicarbonate (Mbic). The dry mater intake (DMI; kg/day) was significantly greater (P < 0.001) in the metabolic cage compared with that in the respiration chamber. The daily CH4 (L/day) emission was strongly correlated (r = 0.78) between CO2T and CO2R. The daily CH4 (L/kg DMI) emission by the CO2T was in the same magnitude as by the CO2R. The measured CO2 (L/day) production in the respiration chamber was not different (P = 0.39) from the calculated CO2 production using the CO2T. This result concludes a reasonable accuracy and precision of CH4 estimation by the CO2T compared with the CO2R.
Keywords: Carbon dioxide; Measurement; Methane; Precision; Respiration chamber.