A data base of over 3,000 ruminant methane emission records from individual animals used to compile New Zealand's greenhouse gas inventory, shows substantial variation in CH4 yields (g/kg dry matter intake (DMI)) within and between forage types. Multiple regression analyses were undertaken using datasets from sheep and cattle fed fresh ryegrass to determine the extent to which variation in CH4 yields could be explained by ryegrass chemical composition. Methane was measured using the SF6 marker dilution technique with sheep and cattle, and also directly by respiration calorimetry from sheep. Data from sheep showed a similar average CH4 yield from both techniques, but there was more variation in SF6 data (23.4 ± 5.73) than from calorimetry (23.1 ± 2.89). Cattle CH4 yields averaged 19.1 ± 3.70 g/kg DMI. Multiple regression analysis of sheep data showed pasture chemical composition accounted for <2% of the variation determined by SF6 and 20% of the variation from calorimetry. Only 13% of the variation in yield from cattle was explained by ryegrass composition, so the majority of variance (>80%) was not explained. We suggest the variation in CH4 emissions is affected by digestive characteristics of individual animals, and interactions with forage physical and chemical components.
Proceedings of the New Zealand Society of Animal Production, Volume 69, Christchurch, 174-178, 2009
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