Comparison of Methods to Measure Methane for Use in Genetic Evaluation of Dairy Cattle

Abstract

Simple SummaryMethane is a greenhouse gas with a global warming potential 28 times that of CO2. Enteric methane accounts for 17% of global methane emissions and 3.3% of total global greenhouse gas emissions from human activities. There is, therefore, significant research interest in finding ways to reduce enteric methane emissions by ruminants. Partners in Expert Working Group 2 (WG2) of the European Cooperation in Science and Technology (COST) Action METHAGENE have used several methods for measuring methane output by individual dairy cattle under various environmental conditions. Methods included respiration chambers, the sulphur hexafluoride (SF6) tracer technique, breath sampling during milking or feeding, the GreenFeed system, and the laser methane detector. Respiration chambers are considered the ‘gold standard’, but are unsuitable for large-scale measurements of methane emissions, which are needed for genetic evaluations. In this study, the suitability of methods for large-scale studies was reviewed and compared. All methods showed high correlations with respiration chambers, but comparisons among alternative methods generally had lower correlations. Results confirm, however, that there is sufficient correlation between methods for measurements from all methods to be combined, with appropriate weightings, for use in international genetic studies. This will pave the way for breeding cattle with lower methane emissions.AbstractPartners in Expert Working Group WG2 of the COST Action METHAGENE have used several methods for measuring methane output by individual dairy cattle under various environmental conditions. Methods included respiration chambers, the sulphur hexafluoride (SF6) tracer technique, breath sampling during milking or feeding, the GreenFeed system, and the laser methane detector. The aim of the current study was to review and compare the suitability of methods for large-scale measurements of methane output by individual animals, which may be combined with other databases for genetic evaluations. Accuracy, precision and correlation between methods were assessed. Accuracy and precision are important, but data from different sources can be weighted or adjusted when combined if they are suitably correlated with the ‘true’ value. All methods showed high correlations with respiration chambers. Comparisons among alternative methods generally had lower correlations than comparisons with respiration chambers, despite higher numbers of animals and in most cases simultaneous repeated measures per cow per method. Lower correlations could be due to increased variability and imprecision of alternative methods, or maybe different aspects of methane emission are captured using different methods. Results confirm that there is sufficient correlation between methods for measurements from all methods to be combined for international genetic studies and provide a much-needed framework for comparing genetic correlations between methods should these become available.

A Review of Enteric Methane Emission Measurement Techniques in Ruminants

“…Open-circuit RC has replaced the earlier closed-circuit RC previously used by Blaxter and Clapperton [ 37 ], providing a relatively simple and accurate way of measuring the heat exchange of animals held within them. Moreover, there are optional sensors for detecting temperature, humidity and pressure installed in some RCs for environmental monitoring [ 38 ]. The size of RCs varies according to the species of animals they are intended to be used with.…”

“…Furthermore, animals require training and acclimatization to withstand enclosure in RCs before being assessed, which requires high labor input and time cost. A greater concern is that measurements of CH 4 production are made under artificial conditions on animals that are restricted in their movements [ 31 , 38 ]. CH 4 emissions and feed intake values gathered under such artificial conditions may not reliably reflect those from the same animal actively grazing a pasture under highly variable environmental conditions (e.g., temperature fluctuations, wind chill, sporadic or heavy levels of rainfall and an uneven distribution of vegetation), [ 46 ] and the maximum intakes for animals are generally lower in RC than in grazing because of the restriction of animal movements [ 36 , 47 ].…”

“…The program installed in GF controls the timing and amount of feed availability for each animal and distributes the measurements evenly in a 24 h feeding cycles [ 63 , 64 ]. Data are uploaded to a cloud-based analysis system in real-time developed by the GF manufacturer for CH 4 emission estimation [ 17 , 38 ].…”

“…Laser CH 4 detector (Tokyo Gas Engineering Solutions Inc., Tokyo, Japan) is a hand-held device that can remotely measure CH 4 concentrations in the air between the LMD and the muzzle of the animal using the infrared absorption spectroscopy technique [ 24 , 76 ]. The distance between the LMD and the animal is in a range of 1 to 3 m and the measurement period is typically between 2 to 4 min each time [ 38 , 58 ]. The unit of the CH 4 concentration is then displayed as parts per million-meter (ppm-m).…”

Genetic Parameters of Different FTIR-Enabled Phenotyping Tools Derived from Milk Fatty Acid Profile for Reducing Enteric Methane Emissions in Dairy Cattle

“…Moreover, respiration chamber environment and management are very different from those of commercial dairy farms. Predictions of EME at the farm level using detectors placed within automatic milking or feeder systems to analyze air methane and carbon dioxide concentrations is also problematic: they do not measure the daily volume of methane emitted and, despite having been proposed as a method for selecting dairy cows [ 5 ], they have shown a low reproducibility and correlation with respiration chambers and other methods [ 6 , 7 , 8 ], opening a wide debate in the scientific community [ 9 , 10 , 11 ].…”