Effects of grain supplementation on methane production of grazing steers using the sulphur (SF6) tracer gas technique

The objective of the study was to examine the effect of supplemental grain on methane (CH4) production of grazing steers. Eight beef steers (344.6 +/- 6.4 kg) were assigned to legume-grass pasture (C; n = 4) or legume-grass pasture plus a rolled barley supplement (S; n = 4). In a completely randomized design with repeated measures, CH4 output was measured for two 24-h periods, using the SF6 tracer gas technique as steers entered (IN) and exited (OUT) paddocks. Two, 4 and 4 kg of rolled-barley grain was fed daily to S steers during the EARLY, MID and LATE periods of the grazing season, respectively. Supplementation reduced forage dry matter intake (DMI) by 11% (P = 0.03) and increased total organic matter intake (TOMI) by 14% (P = 0.001). Daily CH4 production was similar for C and S steers (P > 0.05). Methane production, increased (P < 0.05) from 256 L d(-1) in the EARLY period to 364 L d(-1) at the MID and 342 L d(-1) at the LATE period. Energy lost as CH4, % total gross energy intake (TGEI) ranged from 4.7 to 8.4% (mean 6.5 +/- 0.3%) during the grazing season, and there was no difference between S (6.4 +/- 0.6%) and C (6.7 +/- 0.6%) steers (P = 0.71). Methane production declined with grazing on high-quality forages; steers on EARLY pastures had 44% and 29% lower (P < 0.05) energy loss as CH4 than animals on MID and LATE pastures, respectively. There was also a 54% lower CH4 loss when animals entered new paddocks relative to those exiting the paddocks (P < 0.05). It can be concluded that the effects of supplementation on CH4 production were marginal in grazing steers. The study suggests that pasture quality plays a major role in the extent to which CH4 production can be reduced with grain supplementation in grazing animals.