Enteric methane emission classification and ranking of growing steers during the backgrounding and finishing phases.

There is limited information regarding the effect of beef cattle enteric methane (CH4) classification during the backgrounding and finishing phases and the impact of using metabolic modulators such as growth-promoting implants. This experiment aimed to determine how CH4 and residual CH4 emission (RME) classification impact gas flux and whether implanted or non-implanted growing steers maintain the same CH4 and RME classification during the backgrounding and finishing phases. A total of 46 Angus steers (approximately 8 mo of age and 244 ± 11.1 kg of initial body weight [BW]) were enrolled. During the finishing phase, 23 steers were implanted, while 23 did not receive an implant. Individual animal growth performance and gas flux (CH4 and carbon dioxide [CO2] production and oxygen [O2] consumption) were determined during the backgrounding and finishing phases. In addition, RME was individually determined using metabolic BW and dry matter intake (DMI). In the backgrounding and finishing phases, steers were ranked in ascending order according to their CH4 production (g/d), CH4 yield (g/kg of DMI), CH4 intensity (g/kg of average daily gain), and RME. Consequently, steers were classified as low, medium, and high emitters based on the quartile distribution. Then, gas flux was analyzed using a completely randomized design for each phase. The relationship between the initial CH4 and RME classification during the backgrounding and the subsequent classification during finishing was analyzed using Fisher's exact test. Steers classified as low CH4 or RME had lower (P < 0.05) CH4 production than high emitters during the backgrounding and finishing phases. The production of CO2 varies among classification groups regarding the growing phase and the use of growth-promoting implants. The consumption of O2 was lower (P < 0.05) in steers classified as low CH4 emitters during the backgrounding but not (P > 0.05) during the finishing phase. In addition, between 35% and 83% of the steers re-ranked according to CH4 and RME classification from the backgrounding to the finishing phase. In conclusion, the classification of growing steers using CH4 production, yield, intensity, or RME results in animals with lower CH4 production during the backgrounding and finishing phases. However, CH4 or RME classification should be conducted in each phase because growing steers re-ranked when changing from the backgrounding to the finishing phase.