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    Methane emissions from ruminants fed white clover and perennial ryegrass forages : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2011) Hammond, Kirsty Joan
    Ruminant enteric methane (CH4) emissions account for ~35% of New Zealand’s total greenhouse gas (GHG) emissions and a commitment has been made for their reduction. Previous research suggested lower CH4 yields (g/kg dry matter intake; DMI) from sheep fed white clover (Trifolium repens) compared to perennial ryegrass (Lolium perenne; ryegrass), and the initial focus was to account for that difference. However, measurements undertaken here showed little difference between diets in CH4 yield. The objective of this thesis was amended to better understand causes of variation in CH4 emissions from ruminants fed white clover and ryegrass forages. A database analysis showed greater variation in CH4 yield from sheep fed ryegrass forages with measured intakes using the SF6 technique, compared to respiration chambers (23.4 ± 5.70 vs. 23.1 ± 2.90 g/kg DMI). The composition of ryegrass fed to sheep predicted <2% and 20% of the variation in CH4 yield when derived from SF6 and respiration chamber techniques, respectively. For cattle, the database of CH4 yields determined by SF6 found ryegrass composition accounted for 13% of the variation. Measurements in respiration chambers of CH4 yield from sheep in three experiments reported here, had similar values for white clover and ryegrass (22.6 g/kg DMI), despite higher concentrations of fibre and less crude protein in ryegrass. Feed composition predicted less than 19% of variation in CH4 yield. Measurements of CH4 emissions from sheep fed white clover or ryegrass at multiples of 0.8 to 2.5 the metabolisable energy requirements for maintenance (MEm) showed a decline in CH4 yield of 3.47 g/kg DMI for each multiple of MEm intake above maintenance. Measurements of rumen function and digesta kinetics, suggested the rate of liquid flow through the gastro-intestinal tract, and molar percentages of propionate were the main drivers of a change in CH4 yield with intake. This research has shown minor effects of forage composition on CH4 yield, and has highlighted the importance of digestive function to account for effects of intake and individual variation on methanogenesis. The benefits of high feed intakes for production will be complemented by a low CH4 yield and low emissions per unit of production.
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    Quantifying variation in estimated methane emission from ruminants using the SF6 tracer technique : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2008) Vlaming, Johannes Bernardus
    With the signing of the Kyoto Protocol, New Zealand must reduce its national greenhouse gas emissions. As New Zealand has a large proportion of its national emissions as methane (~31%), and methane (CH4) has a short atmospheric lifetime, it provides a good target for mitigation strategies. The initial aim of this research was to identify high and low CH4-emitting cattle to assess factors that contribute to low CH4 production. Initial studies using the SF6 tracer technique to estimate CH4 production could not identify consistently high and low CH4 emitters. Research was therefore undertaken to confirm whether this was due to high variation in estimated CH4 yields, and to quantify the within- and between-animal variation in CH4 production when using the SF6 technique. This research showed considerable within- (coefficient of variation, CV = 7-10%) and between-animal (CV = 7-18%) variation in CH4 yield (g CH4/kg DMI) over time when using the SF6 technique. This is larger than the within- (CV = 3%) and between-animal (CV = 10%) variation reported for calorimetry. This led to the recommendation that the SF6 technique not be used in identifying animals for high or low CH4 yield. A power analysis was developed based on the measured variances for the SF6 technique. Results from this analysis provide researchers with important information on the number of animals and measurements per animal required when undertaking CH4 experiments. One of the sources of variation with the SF6 technique is the SF6 release from permeation tubes. Estimated CH4 yield increases by approximately 8.5% when going from a release rate of 3 mg SF6/day to a rate of 5 mg SF6/day. Further, an in vitro study indicated that SF6 release from permeation tubes is approximately 8% lower in rumen fluid than in air. While further research is required to confirm these results, they emphasise the need to allow time for the release rate to stabilise in the rumen for 4-5 days prior to undertaking measurements. It also led to the recommendation that release rates used in experiments should be within a narrow range, and balanced across experimental treatments.