School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemEvaluation of fat, nitrate and 3-nitrooxypropanol for reducing enteric methane emissions from ruminants( 2019)Enteric methane produced by ruminants is a dietary inefficiency that contributes to global warming. Feeding diets containing starch to ruminants has been reported to decrease enteric methane emissions. The feeding of methane mitigating agents such as supplemental fat, nitrate and 3-nitrooxypropanol (3- NOP) to ruminants has also been reported to decrease enteric methane emissions, but the degree of methane mitigation may depend upon the basal diet offered to the animal. Furthermore, data are lacking on the net impact of 3-NOP and nitrate on whole farm greenhouse gas (GHG) emissions across different production systems. The aim of this thesis was to quantify the productivity and mitigation potential of these methane mitigating agents when they were included in different diets, and to model the effects of feeding 3-NOP and nitrate on whole farm GHG emissions and on the economics of dairy and beef farms. Initially, the methane mitigating agents were tested in vitro, they decreased methane production (MP) and their methane mitigating efficacies were not affected by basal diet. In the following in vivo experiment feeding supplemental fat to dairy cows decreased methane yield in cows fed either wheat or corn based diets. A modelling study predicted that both 3-NOP and nitrate would decrease whole farm GHG emissions; however, 3-NOP had a greater effect on enteric methane, and thus whole farm emissions, than nitrate. The research of this thesis indicates that the antimethanogenic responses to fat, nitrate and 3-NOP are not affected by substrate type, suggesting that these compounds could be effective in ruminants fed wheat grain, which is routinely fed to ruminants in Australia. Feeding 3-NOP could be economical for beef and dairy farms, depending on the cost of 3-NOP. It is concluded that 3-NOP could make an important contribution to reducing whole farm GHG emissions; however, either a production benefit would have to be demonstrated or a carbon offset method would have to be in place to incentivize its use in the livestock industries.