Evaluation of the laser methane detector to estimate methane emissions from ewes and steers1

Abstract

The laser methane detector (LMD) has been proposed as a method to characterize enteric methane (CH4) emissions from animals in a natural environment. To validate LMD use, its CH4 outputs (LMD-CH4), were compared against CH4 measured with respiration chambers (chamber-CH4). The LMD was used to measure CH4 concentration (µL/L) in the exhaled air of 24 lactating ewes and 72 finishing steers. In ewes, LMD was used on 1 d for each ewe, for 2-min periods at 5 hourly observation periods (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 d. 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 data set, 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 were separated in 2 levels. In ewes, a model with LMD and DMI (adjusted R(2) = 0.92) improved the relationship between DMI and chamber-CH4 alone (adjusted R(2) = 0.79) and between LMD and chamber-CH4 alone (adjusted R(2) = 0.86). In both experiments, chamber-CH4 was best explained by models with length of eructation events (time) and maximum values of CH4 concentration during respiration events (µL/L; 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. Although good indicators of quantity of CH4 were obtained with respiration and eructation CH4, the method needed to separate the data into high and low levels of CH4 was not simple to apply in practice. 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.

Review of current in vivo measurement techniques for quantifying enteric methane emission from ruminants

“…Approximately 13% of CH 4 is produced in the hindgut, where 89% of that (11% of total CH 4 produced) is absorbed into the bloodstream and eliminated via expiration (Ricci et al, 2014).…”

“…Methane arises from microbial activities in the lumen of the gastrointestinal tract. The CH 4 produced can be released from the animal via three routes (Ricci et al, 2014): 1) CH 4 from the rumen and lower gut is absorbed into the blood and exhaled from the lungs via expiration, 2) CH 4 emitted directly from the rumen by eructation, and 3) CH 4 emitted from the hindgut in the flatus. Collectively, expiration and eructation have been encompassed in this review by the term "exhaled" gas, as the majority of eructated gas from the rumen is inhaled into the lungs before being exhaled (Hoerneckie et al, 1965;Berends et al, 2014).…”

“…Monitoring head position is crucial if total air emitted is not collected for measurement of gas concentration, especially for comparative and meaningful short-term measurements of CH 4 . It is also important to measure both absorbed and eructated CH 4 emitted through expiration (both of which can vary amongst animals, diets and time of day; Ricci et al, 2014) otherwise emission may be underestimated if only eructation emission is measured. In this regard, there remains a risk of bias if data are rejected on the basis of number of eructations (e.g.…”

“…Another approach to monitor exhaled air CH 4 concentration is the use of handheld laser CH 4 detectors (LMD) to measure CH 4 concentration in the air between the animal"s nose or mouth and the LMD (Chagunda, 2013;Ricci et al, 2014). Table 1).…”

Assessment of methane emission traits in ewes using a laser methane detector: genetic parameters and impact on lamb weaning performance

“…Pickering et al (2015) and Paganoni et al (2017) indicated genetic variation and small to moderate heritabilities for CH 4 traits in dairy cows and sheep, and Rösler et al (2018) described an individual variation in enteric CH 4 emissions in female goats. Furthermore, the economic benefits from selection scenarios including CH 4 traits (Robinson and Oddy, 2016) suggest consideration of CH 4 or of CH 4 indicator traits into overall sheep breeding goals.…”