Evaluating GreenFeed and respiration chambers for daily and intraday measurements of enteric gaseous exchange in dairy cows housed in tiestalls

The objective of this study was to evaluate the GreenFeed (GF) system and respiration chambers (RC) for daily and intraday measurements of the enteric gaseous exchange, as well as the metabolic heat production, lying behavior, and feed intake (FI) rate of dairy cows at these 2 respective housing conditions (tiestall barn [TSB] vs. RC) during the summer periods. Sixteen multiparous lactating dairy cows were recruited and arranged in a randomized complete block design with a baseline period established for each cow. Cows were given a basal diet (CON) for a baseline period of 7 d and were then fed a 3-nitrooxypropanol (3-NOP)-containing feed for the subsequent 26 d as experimental period. During both the baseline and the last 7 d of treatment period, gaseous exchanges of each animal were measured in the TSB using GF for 8 staggered measurements over 3 d, immediately followed by the measurement in RC for 2 d. Corresponding DMI, milk yield, and behavior parameters (e.g., lying behavior and FI rate) in TSB and RC were recorded. The correlation coefficients of CH₄ and H₂ using raw data were 0.84 and 0.85, respectively. For all gases, correlation coefficients between GF and RC on individual cow level decreased when the marginal fixed effects (e.g., inhibitor and breed) were corrected by a mixed model. There were no differences in daily CH₄ production or intensity between GF and RC (442 vs. 443 g CH₄/d or 16.6 vs. 16.2 g CH₄ /kg MY). However, greater CH₄ yield was measured by GF than RC (19.0 vs. 17.8 g CH₄/kg DMI), driven by a lower DMI (23.3 vs. 24.6 kg/d) when cows were housed in TSB sampled by GF compared with cows being housed and sampled in RC. The correlations for CO₂ production and O₂ consumption were moderate and expected due to the variation associated with the mild heat stress condition during GF measurements in the TSB (temperature-humidity index [THI] 56 vs. 68), as indicated by the reduced lying time (-2.1 h/d). At the intraday level, there was an interaction between techniques and hour-of-day for CH₄ production, as indicated by the discrepancies in postprandial CH₄ emissions between techniques. In summary, this set of results showed that there were strong positive correlations for CH₄ and H₂ emissions between GF and RC based on individual cow data. However, such relationship should be interpreted with caution, given the data clustering resulting from the use of inhibitor 3-NOP. On treatment level, these 2 techniques detected similar inhibitor effect on the estimated daily CH₄ emissions. The intraday patterns of CH₄ and H₂ production captured by GF provided a close approximation for those measured by RC. Nevertheless, potential underestimation may occur, especially following fresh feed delivery. For measuring CO₂ production and O₂ consumption, the GF captured similar intraday variations to those in the RC. However, the estimated daily production and consumption were not directly comparable, which was expected due to the variable thermal conditions during the summer. Further evaluations under the same weather conditions are warranted.