Ricci P, Chagunda M G G, Rooke J, M Houdijk J G, Duthie C-A, Hyslop J, Roehe R, Waterhouse A
Future Farming Systems, SRUC, West Mains Road, Edinburgh, EH9 3JG, UK
Future Farming Systems, SRUC, West Mains Road, Edinburgh, EH9 3JG, UK.
J Anim Sci. 2014 Nov;92(11):5239-50. doi: 10.2527/jas.2014-7676.
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.
激光甲烷探测器（LMD）已被提议作为一种在自然环境中表征动物肠道甲烷（CH4）排放的方法。为验证LMD的用途，将其CH4输出值（LMD-CH4）与呼吸室测量的CH4值（chamber-CH4）进行了比较。LMD用于测量24只泌乳母羊和72头育肥牛呼出空气中的CH4浓度（微升/升）。对于母羊，每只母羊在喂食后的5个每小时观察期（分别为P1至P5）各使用LMD 1天，每次2分钟。对于喂食低精料或高精料日粮的牛，每天使用LMD一次，每次4分钟，共3天。在测量LMD-CH4后的一周，母羊或牛进入呼吸室以量化每日CH4排放量（克/天）。LMD输出由叠加在较低CH4浓度振荡背景上的高CH4浓度周期性事件组成。高CH4事件归因于嗳气，较低的背景CH4归因于呼吸。在对数据集拟合双正态分布后，使用较低分布99%概率的阈值来区分呼吸和嗳气事件。平均LMD-CH4与chamber-CH4之间的相关性不高，仅在将数据分为两个水平后观察到相关性有所改善。对于母羊，包含LMD和干物质采食量（DMI）的模型（调整后R(2)=0.92）改善了单独的DMI与chamber-CH4之间的关系（调整后R(2)=0.79）以及单独的LMD与chamber-CH4之间的关系（调整后R(2)=0.86）。在两个实验中，chamber-CH4最好由包含嗳气事件时长（时间）和呼吸事件期间CH4浓度最大值（微升/升；P<0.01）的模型来解释。不同观察期的方法间相关性有所不同，表明喂食后3至5小时观察到LMD的最佳结果。鉴于LMD使用时间短且操作简便，其具有商业应用和基于实地研究的潜力。尽管通过呼吸和嗳气CH4获得了CH4量的良好指标，但将数据分为高CH4和低CH4水平的方法在实际应用中并不简单。应结合动物采食行为和生理学对LMD进行进一步评估，以验证嗳气和呼吸水平的假设，并且应测试其他变异来源（即微气象学），以更好地研究其在户外条件下进行CH4测试的潜在应用。
