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

Abstract

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.