A pilot study to capture methane from the exhausted air of dairy cows using a cryogenic approach

In the agricultural sector, ruminants are the largest methane (CH4) emission source and many efforts have been undertaken to reduce these greenhouse gas emissions, while compromising animal health and physiology. On the other hand, ruminal CH4, which is biomethane, is in high demand, especially in its liquid form (LBM) that can be used as high energy density fuel. However, CH4 released from a ruminant is immediately mixed with air and highly diluted (<0.1%), challenging CH4 capture technologies. Here we aimed to construct a cryogenic pilot system to capture and liquefy enteric CH4 released from dairy cows kept in respiration chambers. To approach this aim, the outlet air from the chambers was directed through a two-step cooling trap to capture CO2 (-120 to -130 °C) as a solid in the first and CH4 and O2 as liquids in the second cooler (-160 to -180 °C). Warming the second cooler resulted in the evaporation of O2, thereby separating O2 and CH4. LBM purity was in average 90% and was lowest at warming rates higher than 0.88 °C/min. The mean CH4 capture efficiency was 92% and found to be independent of sequestration time and flow rate. However, an increase in CH4 concentration to 0.6%, as it occurs directly at the muzzle of a cow, reduced the sequestration time for CH4. These results show that cryogenic technology can be used to obtain LBM from the air containing ultra-low CH4 concentrations as it is found in cattle barns with high efficiency and purity.

The Berlin-Buch respiration chamber for energy expenditure measurements

PURPOSE

We present a methodological overview of a respiration chamber at the Experimental and Clinical Research Center in Berlin, Germany. Since 2010, we investigated 750 healthy subjects and patients with various diseases. We routinely measure resting energy expenditure (REE), dietary-induced thermogenesis, and activity energy expenditure.

METHODS

The chamber is a pull calorimeter with a total volume of 11,000 L. The majority of measurements is done with a flow rate of 120 L/min, yielding a favorable time constant of 1.53 h. The gas analysis system consists of two paramagnetic O₂ sensors and two infrared CO₂ sensors, one for incoming and one for outgoing air samples. O₂ and CO₂ sensors are calibrated simultaneously before each measurement with a 6 min calibration routine. To verify the accuracy of the whole the calorimetric system, it is validated every 2 weeks by 2 h acetone burning tests.

RESULTS

Validation factors (calculated/measured) of 20 representative 2 h acetone burning tests were 1.03 ± 0.03 for [Formula: see text], 1.02 ± 0.02 for [Formula: see text], 0.99 ± 0.02 for RER, and 1.03 ± 0.03 for EE. Four repeated 60 min REE measurements of a healthy woman showed variabilities of 231.9 ± 4.8 ml/min for [Formula: see text] (CV 2.1%), 166.0 ± 6.3 ml/min for [Formula: see text] (CV 3.8%), 0.73 ± 0.03 for RER (CV 4.6%), and 4.55 ± 0.07 kJ/min for EE (CV 1.6%).

CONCLUSIONS

The data presented show that our respiration chamber produces precise and valid EE measurements with an exceptionally fast responsiveness.

A new experimental setup for measuring greenhouse gas and volatile organic compound emissions of silage during the aerobic storage period in a special silage respiration chamber

The aim of this study was to develop a new experimental setup to determine parallel the emissions of greenhouse gases (GHG) and volatile organic compounds (VOCs) from silage during the opening as well as the subsequent aerobic storage phase of the complete bale without wrapping film. For this purpose, a special silage respiration chamber was used in which a silage bale could be examined. The gas analysis (CO₂, methanol, ethanol, ethyl acetate) of inlet, ambient and outlet air of the silage respiration chamber was carried out by photoacoustic spectroscopy. The gas samples taken inside the bale were analysed by gas chromatography for CO₂, O₂, CH₄, and N₂O. Three silage bales (grass and lucerne) as the smallest silage unit commonly used in practice were examined. The emission behaviour of the bales was recorded during experimental periods up to 55 days. The results allow a differentiation of the outgassing processes. On the one hand, gases produced during the anaerobic ensiling process (CO₂, CH₄, N₂O) are released once in a large amount during the first experimental hours after opening the silage. On the other hand, a continuous outgassing process takes place, which is particularly true for the VOCs ethanol, methanol, and ethyl acetate, whereby VOC emissions increase with rising ambient air temperatures. In this study, the emissions during the first 600 experimental hours from the grass silage bale and lucerne silage bale were 2313 g and 2612 g CO₂, 17.6 g and 145.2 g methanol, 132.3 g and 675.9 g ethanol, 55.1 g and 66.2 g ethyl acetate, respectively. Nevertheless, the focus of this study was on the technical recording of gas concentrations inside the silage bale itself and the emissions in the ambient air of the bale. For a better interpretation of the data, additional factors should be considered in further investigations.

The use of milk Fourier transform mid-infrared spectra and milk yield to estimate heat production as a measure of efficiency of dairy cows

Background

Transformation of feed energy ingested by ruminants into milk is accompanied by energy losses via fecal and urine excretions, fermentation gases and heat. Heat production may differ among dairy cows despite comparable milk yield and body weight. Therefore, heat production can be considered an indicator of metabolic efficiency and directly measured in respiration chambers. The latter is an accurate but time-consuming technique. In contrast, milk Fourier transform mid-infrared (FTIR) spectroscopy is an inexpensive high-throughput method and used to estimate different physiological traits in cows. Thus, this study aimed to develop a heat production prediction model using heat production measurements in respiration chambers, milk FTIR spectra and milk yield measurements from dairy cows.

Methods

Heat production was computed based on the animal’s consumed oxygen, and produced carbon dioxide and methane in respiration chambers. Heat production data included 168 24-h-observations from 64 German Holstein and 20 dual-purpose Simmental cows. Animals were milked twice daily at 07:00 and 16:30 h in the respiration chambers. Milk yield was determined to predict heat production using a linear regression. Milk samples were collected from each milking and FTIR spectra were obtained with MilkoScan FT 6000. The average or milk yield-weighted average of the absorption spectra from the morning and afternoon milking were calculated to obtain a computed spectrum. A total of 288 wavenumbers per spectrum and the corresponding milk yield were used to develop the heat production model using partial least squares (PLS) regression.

Results

Measured heat production of studied animals ranged between 712 and 1470 kJ/kg BW^0.75. The coefficient of determination for the linear regression between milk yield and heat production was 0.46, whereas it was 0.23 for the FTIR spectra-based PLS model. The PLS prediction model using weighted average spectra and milk yield resulted in a cross-validation variance of 57% and a root mean square error of prediction of 86.5 kJ/kg BW^0.75. The ratio of performance to deviation (RPD) was 1.56.

Conclusion

The PLS model using weighted average FTIR spectra and milk yield has higher potential to predict heat production of dairy cows than models applying FTIR spectra or milk yield only.

Comparative methane estimation from cattle based on total CO2 production using different techniques

The objective of this study was to compare the precision of CH₄ estimates using calculated CO_{2 (HP)} by the CO₂ method (CO₂T) and measured CO₂ in the respiration chamber (CO₂R). The CO₂R and CO₂T study was conducted as a 3 × 3 Latin square design where 3 Dexter heifers were allocated to metabolic cages for 3 periods. Each period consisted of 2 weeks of adaptation followed by 1 week of measurement with the CO₂R and CO₂T. The average body weight of the heifer was 226 ± 11 kg (means ± SD). They were fed a total mixed ration, twice daily, with 1 of 3 supplements: wheat (W), molasses (M), or molasses mixed with sodium bicarbonate (Mbic). The dry mater intake (DMI; kg/day) was significantly greater (P < 0.001) in the metabolic cage compared with that in the respiration chamber. The daily CH₄ (L/day) emission was strongly correlated (r = 0.78) between CO₂T and CO₂R. The daily CH₄ (L/kg DMI) emission by the CO₂T was in the same magnitude as by the CO₂R. The measured CO₂ (L/day) production in the respiration chamber was not different (P = 0.39) from the calculated CO₂ production using the CO₂T. This result concludes a reasonable accuracy and precision of CH₄ estimation by the CO₂T compared with the CO₂R.

Classical experiments in whole-body metabolism: open-circuit respirometry-diluted flow chamber, hood, or facemask systems

For over two centuries, scientists have measured gas exchange in animals and humans and linked this to energy expenditure of the body. The aim of this review is to provide a comprehensive overview of open-circuit diluted flow indirect calorimetry and to help researchers to make the optimal choice for a certain system and its application. A historical perspective shows that 'open circuit diluted flow' is a technique first used in the 19th century and applicable today for room calorimeters, ventilated hood systems, and facemasks. Room calorimeters are a classic example of an open-circuit diluted flow system. The broadly applied ventilated hood calorimeters follow the same principle and can be classified as a derivative of these room calorimeters. The basic principle is that the subject breathes freely in a passing airflow that is fully captured and analyzed. Oxygen and CO2 concentrations are measured in inlet ambient air and captured outlet air. The airflow, which is adapted depending on the application (e.g., rest versus exercise), is measured. For a room indirect calorimeter, the dilution in the large room volume is also taken into account, and this is the most complex application of this type of calorimeter. Validity of the systems can be tested by alcohol burns, gas infusions and by performing repeated measurements on subjects. Using the latter, the smallest CV (%) was found for repeated VO2max tests (1.2%) with an SD of approximately 1 kJ min-1. The smallest SD was found for sleeping metabolic rate (0.11 kJ min-1) with a CV (%) of 2.4%.