Methane emissions from ruminants: towards a better understanding of outputs from the Laser Methane Detector

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

Lincoln

Conferencia; 29th Biennial Conference of the Australian Society of Animal Production; 2012

Australian Society of Animal Production

Available techniques to quantify methane (CH4) emissions from ruminants are either expensive, time consuming, raise issues in terms of reliability of results or cannot represent animals’ natural condition. The Laser Methane Detector (LMD) is a relatively cheap hand-held spectroscope which, first used in dairy cows, has been proposed as an alternative method to characterise enteric CH4 emissions from animals in their natural environment. The aim of this work is to propose a new method for the analysis and interpretation of the outputs that can be obtained with this device. The LMD was used to measure CH4 emitted from the mouth and nostril area of 24 lactating Mule ewes fed alfalfa pellets and 72 finishing Aberdeen Angus cross Limousin steers fed TMR of either 75:25 or 8:92 forage to concentrate ratio. The LMD measures the concentration (ppm per metre) of CH4 present between the object and the detector based on infrared-absorption spectroscopy. The dataset consisted of a series of mini-peaks and mini-troughs. Apart from normal breath cycles, episodes of high CH4 concentration were observed, and are presumed to be eructation events. The lower oscillating level is presumed to be CH4 emanating from the lungs. Means of mini-peaks and mini-troughs of CH4 concentration within each event (eructation and respiration) were identified. Results were analysed separately for sheep and cattle using Proc Mixed and correlation between methods with Proc Corr of SAS. Sheep data set was analysed as repeated measurements. In cattle data set, diet was considered as factor.The proportion of CH4 corresponded to CH4 from eructation and respiration agreed with previously reported ranges. CH4 concentrations decreased (p<0.005) from 28±2.7 to 17±1.4 ppm-m as time after offering fresh food increased. The data analysis method produced similar results when applied to cattle, differentiating between eructation and respiration based CH4. As expected, steers offered a high concentrate diet exhibited significantly lower CH4 than those offered a high forage diet (33±3.9 and 73±4.0 ppm-m, respectively, p<0.0001).Overall, this device and data analysis method provide detailed information regarding the biology of CH4 produced by ruminants. It proved capable of both characterising and differentiating between diets and data was correlated with full chamber-based data.