Technical note: test of a low-cost and animal-friendly system for measuring methane emissions from dairy cows.

Methane is a greenhouse gas with a significant anthropogenic contribution from cattle production. A demand exists for techniques that facilitate evaluation of mitigation strategies for dairy cows. Therefore, a low-cost system facilitating the highest possible animal welfare was constructed and validated. The system uses the same principles as systems for open-circuit indirect calorimetry, but to lower the costs, the chamber construction and air-conditioning system were simpler than described for other open-circuit systems. To secure the highest possible animal welfare, the system is located in the cow's daily environment. The system consists of 4 transparent polycarbonate chambers placed in a square so that the cows are facing each other. The chamber dimensions are 183 (width), 382 (length), and 245 cm (height) with a volume of 17 m(3). Flow and concentrations of O(2), CO(2), CH(4), and H(2) are measured continuously in the outlet. Flow is measured with a mass flow meter, O(2) with a paramagnetic sensor, CO(2) and CH(4) with infrared sensors, and H(2) with an electrochemical sensor. Chamber inlet is placed in the barn and background concentrations may differ between chambers, but delta values between background and outlet concentrations for all chambers were within instrument tolerance. Average recovery rates of CO(2) and CH(4) were (mean ± SD) 101 ± 4 and 99 ± 7%, respectively. This is within the expected tolerance of the whole system (gas sensors and flow meters). Feed dry matter intakes were not affected by confining the animals in chambers, as dry matter intake before and during chamber stay were similar. It was concluded that the system delivers reliable values, and the transparent construction in combination with the location in the barn environment prevent negative impact on animal welfare and, thereby, data quality.