Comparison of greenhouse gas emissions from sheep measured using both respiration and portable accumulation chambers

Methane (CH₄) is a potent gas produced by ruminants, and new measurement techniques are required to generate large datasets suitable for genetic analysis. One such technique are portable accumulation chambers (PAC), a short-term sampling method. The objectives of the current study were to explore the relationship between CH₄ and carbon dioxide (CO₂) output measured using both PAC and respiration chambers (RC) in growing lambs, and separately investigate the relationship among CH₄, CO₂ and measured ad libitum DM intake (DMI). Methane, CO₂ and DMI were measured on 30 Suffolk and 30 Texel ewe lambs (age 253 ± 12 days) using the RC and PAC sequentially. The experiment was conducted over a 14-day period, with DMI measured from days 1 to 14; measurements in RC were conducted from days 10 to 12, while measurements in PAC were taken twice, the day immediately prior to the lambs entering the RC (day 9; PAC Pre-RC) and on the day lambs exited the RC (day 13; PAC Post-RC). Greater CH₄ and CO₂ output was measured in the RC than in the PAC (P < 0.01); similarly mean CH₄ yield was greater when measured in the RC (15.39 ± 0.452 g CH₄/kg DMI) compared to PAC (8.01 ± 0.767 g CH₄/kg DMI). A moderate correlation of 0.37 was found between CH₄ output measured in PAC Pre-RC and the RC, the corresponding regression coefficient of CH₄ output measured in the RC regressed on CH₄ output measured in PAC Pre-RC was close to unity (0.74; SE 0.224). The variance of CH₄ and CO₂ output within the measurement technique did not differ from each other (P > 0.05). Moderate to strong correlations were found between CH₄ and CO₂ per kg of live weight and CH₄ and CO₂ yield. Results from this study highlight the suitability of PAC as a ranking tool to rank animals based on their gaseous output when compared to the RC. However, repeated measurements separated by several days may be beneficial if precise rankings are required. Given the close to unity regression coefficient of CH₄ output measured in the RC regressed on CH₄ output measured in PAC Pre-RC suggests that PAC could also be potentially used to estimate absolute CH₄ output; however, further research is required to substantiate this claim. When DMI is unknown, CH₄ and CO₂ per kg of live weight are a suitable alternative to the measurement of CH₄ and CO₂ yield.