Ruminant nutrition and function: understanding methane mitigation routes and impacts
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Date
03/07/2018Author
Cabeza Luna, Irene
Metadata
Abstract
Methane is a potent greenhouse gas with a global warming potential 21 times
that of carbon dioxide. Globally, ruminants are the main anthropogenic contributors
to methane release to the atmosphere. Methane is produced in the gastrointestinal
tract of ruminants, mostly within the rumen by methanogenic archaea. However,
methane production represents a loss of 2 to 12% of dietary gross energy for the
animal, which could otherwise be available for growth or milk production.
Therefore, mitigation of methane production by ruminants could produce both
economic and environmental benefits, with more sustainable and energy efficient
livestock, and offering a promising way of slowing global warming. Despite
extensive research undertaken to find ways of reducing methane emissions from
ruminants, progress has been relatively limited. Furthermore, there is still a lack of
studies linking rumen microbiology and ruminant nutrition and production.
The central purpose of this research was to investigate feed additives to
reduce methane emissions and to understand associated changes that occur in the
rumen microbiota. For the first experiment (Chapter 2), biochar was evaluated as an
antimethanogenic compound for beef cattle. The in vitro gas production technique
was used to study the effects of biochar on rumen fermentation and methane
production. Overall, methane production was reduced by 5% by the addition of
biochar compounds (10 g/kg of substrate). The observed reduction in methane
produced was not associated with a change in volatile fatty acid profile suggesting
biochar primarily inhibited fermentation. Ammonia concentration was significantly
reduced with biochar inclusion. Because different biochars had different effects on
methane production, further investigation of relationships between the
physicochemical properties of biochars and antimethanogenic effects are necessary.
However, due to the small reduction in methane production recorded, research with
biochar was discontinued. Encapsulated nitrate was then explored as an
antimethanogenic additive and as an alternative non-protein nitrogen source to urea
(Chapter 3). The effect of using encapsulated nitrate as a replacement for urea or
dietary protein, plus the addition of inorganic sulphur, on enteric methane emissions,
nutrient digestibility, nitrogen utilization and microbial protein synthesis from
crossbred beef steers were studied. In addition, nitrate toxicity and eating behaviour
were investigated. The inclusion of encapsulated nitrate reduced methane production
compared to urea and a true protein source, with no adverse effects on rumen
fermentation or nitrogen metabolism and no effects with the inclusion of elemental
sulphur. The level of addition of encapsulated nitrate (14.3 g nitrate /kg DM) and the
time of adaptation chosen for this study (14 days) were adequate to avoid nitrate
toxicity. Finally, the effects of adding nitrate inclusion to different basal diets on
rumen microbial populations and relationships of these populations with methane
production were investigated (Chapter 4). The V4 hypervariable regions of the
bacterial and archaea 16S rRNA genes were amplified and sequenced. Effects on
microbial population induced by nitrate were dependant on the basal diet but nitrate
altered specific archaeal and bacterial OTUs consistently between studies. A direct
and strong correlation between some archaea taxonomic groups and OTUs with
methane production was observed.