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

Abstract

Portable accumulation chambers (PAC) enable gaseous emissions from small ruminants to be measured over a 50 min period, to date however, the repeatability of consecutive days of measurement in the PAC has not been investigated. The objectives of this study were to investigate: 1) the repeatability of consecutive days of gaseous measurements in the PAC, 2) the number of days required to achieve precise gaseous measurements, and 3) to develop a prediction equation for gaseous emissions in sheep. A total of 48 ewe lambs (c. 10 to 11 mo of age) were randomly divided into four measurement groups each day, for 17 consecutive days. Gaseous measurements were conducted between 0800 h and 1200 h daily. Animals were removed from perennial ryegrass silage for at least 1 h before measurements in the PAC and animals were assigned randomly to each of the 12 chambers. Methane (CH4; ppm) concentration, oxygen (O2; percentage) and carbon dioxide (CO2; percentage) were measured at 3 time points (0, 25, and 50 min after entry of the first animal into the first chamber). To quantify the effect of animal and day variation on gaseous emissions, between-animal, between-day and error variances were calculated for each gaseous measurement using a linear mixed model. The number of days required to gain a certain precision (defined as the 95% confidence interval (CI) range) for each gaseous measurement was also calculated. For all 3 gases the between-day variance (39% to 40%) accounted for a larger proportion of total variance compared to between-animal variance, while the repeatability of 17 consecutive days of measurement was 0.36, 0.31 and 0.23 for CH4, CO2 and O2, respectively. Correlations between consecutive days of measurement were strong for all 3 gases; the strongest correlation between d 1 and the remaining days for CH4, CO2 and O2 was 0.71 (d 1 and d 6), 0.77 (d 1 and d 2) and 0.83 (d 1 and d 5), respectively. A high level of precision was achieved when gaseous measurements from PAC were taken over 3 consecutive days. The prediction equation over-estimated gaseous production for all 3 gases: the correlations between actual and predicted gaseous output ranged from 0.67 to 0.71, with the r 2 ranging from 0.45 to 0.71. Results from this study will aid the refinement of the protocol for the measurement of gaseous emissions in sheep using the PAC.

Genetic parameters for methane emissions in Australian sheep measured in portable accumulation chambers in grazing and controlled environments

“…Elsewhere, a repeatability of 0.55 has been reported for methane emission measure in respiration chambers with a 10-15-day interval and as high as 0.94 for measurements on no et al consecutive days (Pinares-Pati ˜ 2013). The moderate repeatabilities also align with what was estimated for Merino ewes in a controlled environment (0.17-0.40) (Dominik and Oddy 2015), lambs and ewes grazing pastures (0.33-0.55) in New Zealand (Jonker et al 2018), ewe lambs measured for 17 days in a controlled environment (0.36) in Ireland (O'Connor et al 2021) and the phenotypic correlation (0.59) between two PAC measurement protocols in a controlled environment in Australia (Robinson et al 2020). Moderate repeatabilities for methane emission (0.23 and 0.59), carbon dioxide emission (0.34 and 0.51) and oxygen uptake (0.38 and 0.53) in both environments suggest that there is benefit in having repeated measurements for genetic evaluation to rank animals for selection.…”

Enteric methane emission reduction potential of natural feed supplements in ewe diets

“…Finally, data generated from PAC are repeatable over an extended time period, and provide useful information on CH 4 emissions ( Robinson et al, 2016 ; O’Connor et al, 2021b ). However, PAC cannot be deployed for long periods of time (>50 min) as increased CO 2 concentration can negatively influence measurements.…”

“…Methane measurements were recorded at the end of the covariate week, weeks 6 and 8 of experiment 1 and weeks 5, 7, and 8 of experiment 2 using portable accumulation chambers ( PAC ) as described by Jonker et al. (2018) and O’Connor et al. (2021) .…”

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

“…PAC were used to obtain CH 4 , oxygen (O 2 ), and CO 2 measurements as described by O’ Connor et al (2021b) . PAC were designed by AgResearch using the Mark III apparatus construction, with 12 individual chambers mounted on a trailer ( www.agresearch.co.nz , Steve Gebbie pers.…”

“…Between lots, a gas extraction vacuum system was used to remove all residual CH 4 and CO 2 . The CH 4 , O 2, and CO 2 measurements obtained from PAC were expressed in grams per day as described by O’ Connor et al (2021b) . A total of 1,726 records on CH 4 and CO 2 output were generated for analysis with the number of animals and records per life stage shown in Table 1 .…”