Evaluation of the Laser Methane Detector to estimate methane emissions from ewes and steers

RICCI P; CHAGUNDA MGG; ROOKE J; HOUDIJK J; DUTHIE C-A; HYSLOP J; ROEHE R; WATERHOUSE A

JOURNAL OF ANIMAL SCIENCE

AMER SOC ANIMAL SCIENCE

Año: 2014

0021-8812

The Laser Methane Detector (LMD) has been proposed as a method to characterize enteric methane (CH4) emissions from animals in their natural environment. However, LMD is not capable of quantifying CH4 without it validation with another method. This work aimed to compare LMD-CH4 outputs against respiration chamber measurements (chamber-CH4). The LMD was used to measure CH4 concentration (ppm) in the exhaled air of 24 lactating ewes and 72 finishing steers. In ewes, LMD was used on 1 day for each ewe, for 2 min periods at 5 hourly intervals (P1 to P5, respectively) after feeding. In steers fed either low or high-concentrate diets, LMD was used once daily for a 4 min period for 3 days. The week after LMD-CH4 measurement, ewes or steers entered respiration chambers to quantify daily CH4 output (g/d). The LMD outputs consisted of periodic events of high CH4 concentrations superimposed on a background of oscillating lower CH4 concentrations. The high CH4 events were attributed to eructation and the lower background CH4 to respiration. After fitting a double normal distribution to the dataset, a threshold of 99% of probability of the lower distribution was used to separate respiration from eructation events. The correlation between mean LMD-CH4 and chamber-CH4 was not high, and only improved correlations were observed after data was separated in 2 levels. In ewes, a model with LMD and DMI (AdjR2 = 0.92) improved the relationship between DMI and chamber-CH4 alone (AdjR2 = 0.79), and LMD and chamber-CH4 alone (AdjR2 = 0.86). In both experiments, chamber-CH4 was explained best by models with length of eructation events (time) and maximum values of CH4 concentration during respiration events (ppm; P < 0.01). Correlation between methods differed between observation periods, indicating the best results of the LMD were observed from 3 to 5 h after feeding. Given the short time and ease of use of LMD there is potential for its commercial application and field-based studies. However, to get good indicators of quantity of CH4, the method needed to separate respiration- from eructation-CH4 was not simple to apply in practice being quite laborious. Further assessment of the LMD should be performed in relation to animal feeding behavior and physiology to validate assumptions of eructation and respiration levels, and other sources of variation should be tested (i.e. micrometeorology) to better investigate its potential application for CH4 testing in outdoor conditions.