Methane emissions from weaned lambs measured at 13, 17, 25 and 35 weeks of age compared with mature ewes consuming a fresh forage diet

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Daily methane (CH4) emissions and dry matter intake (DMI) were measured on 14 mature ewes (3–4 years old) and 13 lambs when the lambs were 13, 17, 25 and 35 weeks of age. During the four CH4 measurement periods, all animals were kept in individual metabolism cages and fed pasture cut daily and fed at 1.5 times maintenance. Feed was offered in equal amounts at 0800 and 1500 hours daily. Methane emissions were measured using the sulfur hexafluoride tracer technique and values reported were the mean of measurement on 4–5 days for each animal. In the intervals between CH4 measurements, ewes and lambs grazed separate paddocks containing predominantly ryegrass. Daily CH4 emissions for the ewes ranged from 21.5 to 22.5 ± 1.50 g/day and were significantly higher than those of the lambs which ranged from 10.7 to 17.5 ± 1.50 g/day. Averaged across all four periods, the overall mean CH4 emission for lambs was 8% lower (P < 0.05) than for ewes (21.9 v. 23.8 ± 0.95 g CH4/kg DMI). However, within each measurement period, the emissions of CH4/kg DMI from lambs was significantly lower (P < 0.05) than those of ewes only in the fourth period when the lambs were 35 weeks of age (17.9 v. 21.9 g/kg DMI for lambs and ewes, respectively). The pasture offered to both ewes and lambs in this period was of higher quality than in the other periods (organic matter digestibility of 80% DM v. 68–71% DM at other times) and CH4 emission per kg DMI was lower in both groups of animals than in the other periods. This study supports the hypothesis that young sheep have lower CH4 emissions per unit of intake than mature animals. However, the age at which the lambs produced similar CH4/kg DMI to adult sheep could not be determined precisely because of the changes in pasture quality between different measurement periods.