Comparison of methods to determine methane emissions from dairy cows in farm conditions

Abstract

Nutritional and animal-selection strategies to mitigate enteric methane (CH4) depend on accurate, cost-effective methods to determine emissions from a large number of animals. The objective of the present study was to compare 2 spot-sampling methods to determine CH4 emissions from dairy cows, using gas quantification equipment installed in concentrate feeders or automatic milking stalls. In the first method (sniffer method), CH4 and carbon dioxide (CO2) concentrations were measured in close proximity to the muzzle of the animal, and average CH4 concentrations or CH4/CO2 ratio was calculated. In the second method (flux method), measurement of CH4 and CO2 concentration was combined with an active airflow inside the feed troughs for capture of emitted gas and measurements of CH4 and CO2 fluxes. A muzzle sensor was used allowing data to be filtered when the muzzle was not near the sampling inlet. In a laboratory study, a model cow head was built that emitted CO2 at a constant rate. It was found that CO2 concentrations using the sniffer method decreased up to 39% when the distance of the muzzle from the sampling inlet increased to 30cm, but no muzzle-position effects were observed for the flux method. The methods were compared in 2 on-farm studies conducted using 32 (experiment 1) or 59 (experiment 2) cows in a switch-back design of 5 (experiment 1) or 4 (experiment 2) periods for replicated comparisons between methods. Between-cow coefficient of variation (CV) in CH4 was smaller for the flux than the sniffer method (experiment 1, CV=11.0 vs. 17.5%, and experiment 2, 17.6 vs. 28.0%). Repeatability of the measurements from both methods were high (0.72-0.88), but the relationship between the sniffer and flux methods was weak (R(2)=0.09 in both experiments). With the flux method CH4 was found to be correlated to dry matter intake or body weight, but this was not the case with the sniffer method. The CH4/CO2 ratio was more highly correlated between the flux and sniffer methods (R(2)=0.30), and CV was similar (6.4-8.8%). In experiment 2, cow muzzle position was highly repeatable (0.82) and influenced sniffer and flux method results when not filtered for muzzle position. It was concluded that the flux method provides more reliable estimates of CH4 emissions than the sniffer method. The sniffer method appears to be affected by variable air-mixing conditions created by geometry of feed trough, muzzle movement, and muzzle position.

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

“…A positive relationship (r 2 = 0.79, P < 0.001) between MER during milking on-farm and total daily CH 4 emission measured in respiration chambers for the same animals (n = 12) was reported (Table 1). In contrast, Huhtanen et al (2015) compared measurements of eructated CH 4 concentration with CH 4 emission measured using the GreenFeed system (two experiments with n = 32 and n = 59 lactating dairy cows) and found between-cow coefficient of variation (CV) was smaller for GreenFeed compared with eructated CH 4 concentration, and there was no relationship between the measurements of the two methods (r 2 = 0.09; Table 1). …”

“…Consequently, CH 4 emissions will be overestimated for the more efficient cow, partly due to true increases in the CH 4 :CO 2 ratio and partly because of the overestimation of CO 2 production with improved feed efficiency (Huhtanen et al 2015). Furthermore, changes in digestive and metabolic activity at a fixed level of feed intake can affect CO 2 emission, as well as variation in rumen fermentation, and thereby change the CH 4 :CO 2 ratio, the estimated CO 2 emission and thus predicted CH 4 emission (Huhtanen et al, 2015).…”

“…Furthermore, changes in digestive and metabolic activity at a fixed level of feed intake can affect CO 2 emission, as well as variation in rumen fermentation, and thereby change the CH 4 :CO 2 ratio, the estimated CO 2 emission and thus predicted CH 4 emission (Huhtanen et al, 2015).…”

“…The GreenFeed system (C-Lock Inc., Rapid City, South Dakota, USA) is a static short-term measurement device that measures CH 4 (and other gases including CO 2 ) emission from individual cattle by integrating measurements of airflow, gas concentration, and detection of head position during each animal"s visit to the unit (Zimmerman and Zimmerman, 2012;Huhtanen et al, 2015). The system (Figure 3) measures gas emission using a combination of an extractor fan and sensors which induce a measured airflow past the animal"s head, allowing emitted air to be collected and sampled.…”

“…The concentration of CH 4 (and CO 2 and O 2 ) in the sample is measured using non-dispersive infrared analysis. Daily CH 4 emission (F c ; L/min) is calculated using volumetric airflow rate (Q air ) adjusted to STP and corrected for capture rate, as detailed by Huhtanen et al (2015;Equation 2):…”