Greenhouse gases measurement time reduction in Portable Accumulation Chambers with grazing sheep evaluated morning and afternoon

Portable Accumulation Chambers (PAC) represent an important tool for quantifying greenhouse gases (GHG) in small ruminants. The objectives of the study were to evaluate to reduce the PAC time evaluation in sheep without compromising the GHG, methane (CH4) and carbon dioxide (CO2) measurements and to evaluate the PAC methodology, considering the variability of gaseous emissions in the day. Four times the animals spent in the PAC (10, 20, 30 and 40 minutes) and two collection times during the day (morning and afternoon) were tested for two consecutive days. The sheep used in the study came from a field experiment where they were subjected to different grazing feeding systems (only Italian ryegrass, Italian ryegrass in a mixture of legumes (Persian clover (Trifolium resupinatum L.) and White clover (Trifolium repens L.)) pasture and lambs grazing Italian ryegrass and consuming an energetic supplement (RyeG + Sup)). The gas samples collected at PAC were analyzed for CH4 and CO2 concentration on a gas chromatograph. There was no interaction in CH4 and CO2 measurements between times, shifts and grazing feeding systems (p > 0.05). CH4 emission between times did not differ (p > 0.05), while CO2 emissions were higher in the first 10 minutes of measurement and lower in the remaining times, fitting the non-linear regression model, with a reduction until 27.7 minutes. In relation to shifts, there was a difference for CH4 (p < 0.01), and CO2 (p = 0.01) with the highest emissions of CH4 (21.7 ± 4.3 g/day) and CO2 (1282 ± 332 g/day) found in the afternoon. The results of this study indicate that 27.7 minutes of sheep staying in the PAC is enough to evaluate CH4 and CO2 emissions and to improve the estimate of the gas emissions, evaluations should be carried out in the morning and afternoon. [Display omitted] •It is important to measure greenhouse gases (GHG) in sheep.•Portable Accumulation Chambers (PAC) can measure GHG emissions in sheep.•The length of stay in the PAC and the day shifts must be considered for measurements.•Sheep must remain inside the PAC to measure gases for at least 27.7 minutes.•Gas emissions measurements by sheep must be carried out in morning and afternoon.