Enteric methane emissions from low– and high–residual feed intake beef heifers measured using greenfeed and respiration chamber techniques

The objectives of this study were to evaluate the relationship between residual feed intake (RFI; g/d) and enteric methane (CH4) production (g/ kg DM) and to compare CH4 and carbon dioxide (CO2) emissions measured using respiration chambers (RC) and the GreenFeed emission monitoring (GEM) system (C-Lock Inc., Rapid City, SD). A total of 98 crossbred replacement heifers were group housed in 2 pens and fed barley silage ad libitum, and their individual feed intakes were recorded by 16 automated feeding bunks (GrowSafe, Airdrie, AB, Canada) for a period of 72 d to determine their phenotypic RFI. Heifers were ranked on the basis of phenotypic RFI, and 16 heifers (8 with low RFI and 8 with high RFI) were randomly selected for enteric CH4 and CO2 emissions measurement. Enteric CH4 and CO2 emissions of individual animals were measured over two 25-d periods using RC (2 d/period) and GEM systems (all days when not in chambers). During gas measurements metabolic BW tended to be greater (P ≤ 0.09) for high-RFI heifers but ADG tended (P = 0.09) to be greater for low-RFI heifers. As expected, high- RFI heifers consumed 6.9% more feed (P = 0.03) compared to their more efficient counterparts (7.1 vs. 6.6 kg DM/d). Average CH4 emissions were 202 and 222 g/d (P = 0.02) with the GEM system and 156 and 164 g/d (P = 0.40) with RC for the low- and high-RFI heifers, respectively. When adjusted for feed intake, CH4 yield (g/kg DMI) was similar for high- and low-RFI heifers (GEM: 27.7 and 28.5, P = 0.25; RC: 26.5 and 26.5, P = 0.99). However, CH4 yield differed between the 2 measurement techniques only for the high-RFI group (P = 0.01). Estimates of CO2 yield (g/kg DMI) also differed between the 2 techniques (P ≤ 0.03). Our study found that high- and low-effi-ciency cattle produce similar CH4 yield but different daily CH4 emissions. The 2 measurement techniques differ in estimating CH4 and CO2 emissions, partially because of differences in conditions (lower feed intakes of cattle while in chambers, fewer days measured in chambers) during measurement. We conclude that when intake of animals is known, the GEM system offers a robust and accurate means of estimating CH4 emissions from animals under field conditions.