Association of residual methane emission classifications with intake, growth performance, feed efficiency, feeding...

Residual methane (CH₄) emissions (RME) have been proposed as a trait to identify low-emitting ruminants independent of intake and body weight. There is limited understanding of the biological mechanisms underlying the variation in CH₄ emissions in animals with similar body weight (BW) and growth rate. This study evaluated the effects of divergent RME classifications on dry matter intake (DMI), growth performance, feed efficiency, feeding behavior, enteric CH₄ emissions, and ruminal fermentation in crossbred beef cattle fed a forage-based diet. Eighty crossbred beef cattle (19 steers, 61 heifers; 463 ± 57 kg initial BW; mean age 551 ± 22 days) were monitored for 84 d using automated feed intake bunks and a GreenFeed Emission Monitoring (GEM) system. Residual CH₄ emission was computed for individual animals as the residuals from a model regressing CH₄ emission on DMI and metabolic BW. Animals were ranked and classified as low RME (RME < 0.5 SD below the mean, n = 25), medium RME (RME ± 0.5 SD above and below the mean, n = 27), or high RME (RME > 0.5 SD above the mean, n = 26). The RME classification did not affect (P ≥ 0.39) DMI, average daily gain (ADG), or metabolic BW. A tendency (P = 0.08) was observed towards a lower gain-to-feed ratio in low RME animals relative to medium and high RME counterparts. Feeding behavior traits, including bunk visit duration and eating rate, were unaffected (P ≥ 0.80) by RME, although low RME animals tended to have fewer bunk visits (P = 0.08). Enteric gas fluxes were markedly different across groups: low RME cattle produced 20% less CH₄ (163 vs. 205 g/d; P < 0.001), 20% less CH₄ yield (17.9 vs. 22.4 g/kg DMI; P < 0.001), and 21% less CH₄ per MBW (1.51 vs. 1.92 g/kg BW^0.75; P < 0.001) compared with high RME animals. Carbon dioxide (CO₂) production was 8% lower (P < 0.01) and H₂ tended to be lower (P = 0.06) in the low RME group. Molar proportions of volatile fatty acids (VFAs) exhibited no differences between low and high RME cattle. Residual methane emission was positively correlated with CH₄ production (r = 0.81), CH₄ yield (r = 0.63), CH₄ per MBW (r = 0.88), G:F (r = 0.26) and negatively correlated with RFI (r = -0.14). Collectively, these findings demonstrate that cattle divergently classified for low RME produce substantially less CH₄ without compromising ADG. Although a tendency toward reduced feed efficiency was observed, the biological relevance of this difference warrants further investigation, particularly given the diet-type and mixed-sex population evaluated. These results support RME as a biologically meaningful and applicable selection trait for CH₄ mitigation in beef production systems.