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

Abstract

The objective of the study was to examine the effect of supplemental grain on methane (CH 4 ) 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 plusa rolled barley supplement (S; n = 4). In a completely randomized design with repeated measures, CH 4 output was measured for two 24-h periods, using the SF 6 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 steersduring 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 CH 4 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 CH 4 , % 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 CH 4 than animals on MID and LATE pastures, respectively. There was also a 54% lower CH 4 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 CH 4 production were marginal in grazing steers. The study suggests that pasture quality plays a major role in the extent to which CH 4 production can be reduced with grain supplementation in grazing animals. Key words: Methane, grazing steers, grain supplementation, pasture quality