Evaluation of the greenfeed system for methane estimation from grazing dairy cows : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Animal Science [at Massey University, Palmerston North, New Zealand]
Ruminant methane (CH4) production contributes ~32% of New Zealand’s total greenhouse gases (GHG) and a reduction in emissions is required under the Kyoto Protocol. Under this agreement, New Zealand has pledged to either reduce, or take responsibility for the GHG emissions above those in 1990. GHG emission factors used for inventory need to be accurate, reliable and applicable to animals grazing in New Zealand. Furthermore, identification and implementation of mitigation strategies also depends on accurate and reliable methods for measuring CH4 emissions.
Current techniques to measure CH4 have to compromise between accuracy and applicability. Respiration chambers are accurate, but do not represent a grazing environment, whilst the Sulphur Hexafluoride (SF6) technique can be used at grazing, but has more variation than the chambers. Consequently, a new technique known as the Greenfeed system, has been developed to measure CH4 from grazing animals. The evaluation of this technique applied to grazing animals, with minimal interference from humans, and its evaluation is reported here.
In the first experiment, CH4 measurements were compared from the Greenfeed system with respiration chambers and the SF6 technique using six dry dairy cows fed a silage-based diet. Intakes were measured and were approximately at maintenance levels and feeding regimens were similar throughout. The mean CH4 production (g CH4/d) ± standard deviation (Murray et al., 2001) from the Greenfeed unit (150 ± 20.2) was higher and more variable than those from the respiration chambers (134 ± 9.8) and the SF6 technique (128 ± 8.7). Similarly, the CH4 yield (g CH4/kg dry matter intake (DMI)) ± SD was higher from the Greenfeed unit (24.0 ± 3.2) than the respiration chambers (21.9 ± 1.6) or the SF6 technique (20.5 ± 1.4). Correlations between CH4 production by individual animals using the Greenfeed system and either respiration chambers or the SF6 technique were weak (r = -0.36 and 0.13, respectively).The second experiment successfully implemented two Greenfeed units on-farm with 24 lactating cows, including four with rumen fistulae, and evaluated their behavioural interactions and estimated CH4 production. Seventeen of the 24 cows (approximately 70%) visited the Greenfeed units, but this could be increased by training so most cows visit. An attractant/reward was used to encourage cows into the units and the cows preferred the Lucerne pellets to the Grain pellets. The mean CH4 production measured using the Greenfeed units were 340.3 ± 61.8 g CH4/d, suggesting about 21.3 g CH4/kg DMI (based on calculated feed intakes). It appears that 14 days are needed for cows to get used to the Greenfeed units, and extending estimates (for five further weeks) did not reduce the variance in CH4 emissions values within cows.
This research has shown that the Greenfeed system seems adequate for estimating CH4 production of a whole herd. Further estimates are required before standard operating procedures can be determined and that confidence can be placed in the accuracy of CH4 estimates.