Estimating Enteric Methane Emission from Beef Heifers with Different Residual Feed Intake Using Greenfeed and Respiration Chambers

Greenhouse gas emission from the livestock sector is mainly contributed from enteric methane (CH₄) production. Improving feed efficiency to reduce CH₄ emission while maintaining productivity as well as accurate and robust measurement is of great environmental and economic importance. The objectives of this study were to: compare CH₄ emissions measured using respiration chambers (RC) and the GreenFeed (GF) emission monitoring system and evaluate the relationship between residual feed intake (RFI) and enteric CH₄ production. Sixteen crossbred replacement heifers (8 low-RFI, 8 high-RFI, 377 kg initial BW) were used to measure enteric CH₄ emission. Heifers were group-housed in a pen and fed barley silage ad libitum and their individual feed intakes were recorded by automated feeding bunks. Heifers also received pellets dispensed from the GF emission monitoring system, used to attract and keep the animals in the unit for emission measurement. Enteric CH₄ emission of individual animals was measured over two 25-d periods using RC (2 days/period) and GF systems (all days when not in chambers). Data were analyzed using the mixed procedure of SAS and differences are discussed at P ≤ 0.05. Estimates of CH₄ (g/d) were greater for GF than RC (P < 0.001), but for CH₄ yield the systems only differed for the high-RFI cattle (P = 0.01). Average CH₄ emission was 202 and 222 g/d (P = 0.02) from the GF system, and 156 and 164 g/d (P = 0.40) in RC for the low- and high-RFI heifers, respectively. 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). However, when adjusted for feed intake, CH₄ yield (g/kg DMI) was similar for high- and low-RFI heifers (GF: 27.7 and 28.5, P = 0.25; RC: 26.5 and 26.5, P = 0.99). Intake declined for both groups when they were moved to the RC, and as such DMI was similar (P = 0.29) between groups when they were in the chambers. Our study found that the two measurement techniques differ in estimating CH₄ emission, partially due to differences in conditions (lower feed intakes of cattle while in chambers, fewer days measured in chambers) during measurement. Furthermore, high- and low-efficiency cattle produce similar CH₄ yield but different daily CH₄ emission. We conclude that, when intake of animals is known, the GF offers a robust and accurate means of estimating CH₄ emissions from animals under field conditions.