Investigation of intra-day variability of gaseous measurements in sheep using portable accumulation chambers

Abstract

Portable accumulation chambers (PAC) enable short term spot measurements of gaseous emissions including methane (CH4), carbon dioxide (CO2) and oxygen (O2) consumption from small ruminants. To date the differences in morning and evening gaseous measurements in the PAC have not been investigated. The objectives of this study were to investigate: 1) the optimal measurement time in the PAC, 2) the appropriate method of accounting for the animal’s size when calculating the animal’s gaseous output, and 3) the intra-day variability of gaseous measurements. A total of 12 ewe lambs (c. 10 to 11 months of age) were randomly selected each day from a cohort of 48 animals over nine consecutive days. Methane emissions from the 12 lambs were measured in 12 PAC during two measurement runs daily, AM (8 to 10 h) and PM (14 to 16 h). Animals were removed from Perennial ryegrass silage for at least 1 hour prior to measurements in the PAC and animals were assigned randomly to each of the 12 chambers. Methane (ppm) concentration, O2 and CO2 percentage were measured at 5 time points (T1 = 0.0 min, T2 = 12.5 min, T3 = 25.0 min, T4 = 37.5 min and T5 = 50.0 min from entry of the first animal into the first chamber) using an Eagle 2 monitor. The correlation between time points T5-T1 (i.e. 50 min minus 0 min after entry of the animal to the chamber) and T4-T1 was 0.95, 0.92 and 0.77 for CH4, O2 and CO2, respectively (P<0.01). The correlation between CH4 and CO2 output and O2 consumption, calculated with live-weight and with body volume was 0.99 (P<0.001). The correlation between the PAC measurement recorded on the same animal in the AM and PM measurement runs was 0.73. Factors associated with CH4 production included: day and time of measurement, the live-weight of the animal and the hourly relative humidity. Results from this study suggest that the optimal time for measuring an animal’s gaseous output in the PAC is 50 min, that live-weight should be used in the calculation of gaseous output from an animal and that the measurement of an animal’s gaseous emissions in either the AM or PM does not impact on the ranking of animals when gaseous emissions are measured using the feeding and measurement protocol outlined in the present study.

Repeatability of gaseous measurements across consecutive days in sheep using Portable accumulation chambers

“…The experiment was conducted over 17 consecutive days in 2020. For the purpose of this experiment, CH4, oxygen (O 2 ) and carbon dioxide (CO 2 ) measurements were obtained using 12 PAC as described by O′ Connor et al (2021) using a trailer mounted AgResearch designed and constructed Mark III apparatus ( www.agresearch.co.nz , Steve Gebbie pers. com.).…”

“…A gas extraction vacuum system is fitted on each of the 12 chambers which allowed for the removal of all residual gases from the chambers between measurement runs. The CH 4 measurements obtained for each animal over each measurement run were converted to liter/h (l/h) using the equation as described by O′Connor et al (2021) :…”

“…For each of the above equations, the final gas volume obtained in l/hour can be extrapolated up to a g/d value as described by O′Connor et al (2021): …”

“…To reduce methane (CH 4 ) emissions from ruminants, an understanding of the factors associated with these emissions, as well as the ability to measure animals in their natural environment with low-cost, accurate techniques, is required ( Robinson et al, 2020 ). One such technique is using portable accumulation chambers ( PAC s), a spot sampling method that enables gaseous emissions from sheep to be measured over a 50-min period ( Jonker et al, 2018 ; O′Connor et al, 2021 ). However, research is required to ensure that these PAC measurements are indicative of actual emissions, are repeatable over time, and can be quantified accurately with as few measurements as possible.…”

Methane output across life stages in sheep, how it differs from lambs to adult ewes using portable accumulation chambers

“…Therefore, the measurement and development of mitigation strategies for CH 4 output from ruminant animals is becoming increasingly important to help address the climate change challenge ( Pickering et al, 2015 ). Portable accumulation chambers (PAC) have been validated under Irish conditions ( O’ Connor et al, 2024 ) and enable the measurement of large cohorts of animals over a short period in their natural environment ( Jonker et al, 2018 ; O’ Connor et al, 2021a ). A profile of an animal’s CH 4 output at each life stage is required to develop an understanding of how CH 4 output changes throughout the production cycle from lambs to mature ewes.…”