Laser methane detector-based quantification of methane emissions from indoor-fed Fogera dairy cows

Abstract

Objective: Portable laser methane detectors (LMDs) may be an economical means of estimating CH<sub>4</sub> emissions from ruminants. We validated an LMD-based approach and then used that approach to evaluate CH<sub>4</sub> emissions from indigenous dairy cows in a dryland area of Ethiopia. Methods: First, we validated our LMD-based approach in Simmental crossbred beef cattle (n = 2) housed in respiration chambers and fed either a high- or low-concentrate diet. From the results of the validation, we constructed an estimation equation to determine CH<sub>4</sub> emissions from LMD CH<sub>4</sub> concentrations. Next, we used our validated LMD approach to examine CH<sub>4</sub> emissions in Fogera dairy cows grazed for 8 h/d (GG, n = 4), fed indoors on natural-grassland hay (CG1, n = 4), or fed indoors on Napier-grass (<i>Pennisetum purpureum</i>) hay (CG2, n = 4). All the cows were supplemented with concentrate feed. Results: The exhaled CH<sub>4</sub> concentrations measured by LMD were linearly correlated with the CH<sub>4</sub> emissions determined by infrared-absorption-based gas analyzer (r<sup>2</sup> = 0.55). The estimation equation used to determine CH<sub>4</sub> emissions (y, mg/min) from LMD CH<sub>4</sub> concentrations (x, ppm m) was y = 0.4259x+38.61. Daily CH<sub>4</sub> emissions of Fogera cows estimated by using the equation did not differ among the three groups; however, a numerically greater milk yield was obtained from the CG2 cows than from the GG cows, suggesting that Napiergrass hay might be better than natural-grassland hay for indoor feeding. The CG1 cows had higher CH<sub>4</sub> emissions per feed intake than the other groups, without significant increases in milk yield and body-weight gain, suggesting that natural-grassland hay cannot be recommended for indoor-fed cows. Conclusion: These findings demonstrate the potential of using LMDs to valuate feeding regimens rapidly and economically for dairy cows in areas under financial constraint, while taking CH<sub>4</sub> emissions into consideration.

Measuring Livestock CH4 Emissions with the Laser Methane Detector: A Review

“…Most studies used a measurement interval of 0.5 s (i.e., two CH 4 values per second, the default setting of the LMD) [18,35,36]. Roessler et al [26] recommended the use of 0.1 s-the shortest possible measurement interval-after showing that reducing data points to simulate a 1 or 4 s measurement interval resulted in increasing deviation of mean CH 4 values from the mean of the full data set.…”

“…LMD measurements were performed at different locations inside buildings: in RC, e.g., [18,36]; in free-stalls, e.g., [12,14]; in a tie-stall [17]; in the milking parlour (according to the author's experience); a weighing facility for sheep [15]; and in individual pens, e.g., [38,42]. A few studies have been conducted on pasture [31,32,43] or in other half or full outdoor locations [19].…”

“…A deletion of entire recordings was described in one study, where profiles were not categorisable into one of two fitted normal distributions (one for eructation and one for respiration; see step: "Separation of eructation from respiration") [18]. A more intuitive approach would be to plot all profiles and visually inspect the plots for any distinct deviation from the natural pattern of peaks and troughs.…”

“…Regardless of which variant is chosen, it should be ensured that unphysiologically high single values are detected and deleted. Another source of faulty data is the movement of the animal, which can lead to a time-and labour-consuming removal of data from times when the laser beam was off-target [18,31].…”

“…In recent years, it has also been used to detect CH 4 concentrations in exhaled air from animals. Since the first known application for this purpose in 2009 by Chagunda et al [12], researchers have further developed and evaluated the measurement, refined the analysis of data obtained with the LMD, and applied the LMD in studies on genetic analyses [13][14][15], on nutrition and feed efficiency [16][17][18], on the physiological status of animals [15], and to characterize different husbandry systems [19]. So far, measurements with the LMD have been carried out mostly on dairy cows, but also on sheep, beef cattle, and goats.…”