Author(s) |
Villar, Maria Laura
Hegarty, Roger
Godwin, Ian
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Publication Date |
2019-07-08
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Abstract |
Please contact rune@une.edu.au if you require access to this thesis for the purpose of research or study.
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Abstract |
<p>Global methane (CH<sub>4</sub>) emissions from ruminant livestock have continued to increase in the last decade due to the global ruminant population increasing in response to growing demand for livestock products. Supplementing the diet of ruminants with nitrate (NO<sub>3</sub>) is an effective strategy to reduce enteric CH<sub>4</sub> emissions and also provides additional non-protein nitrogen for the growth of rumen microorganisms. However, there is a risk of nitrite (NO<sub>2</sub>) toxicity in ruminants after feeding NO<sub>3</sub> that is unpredictable because of the large between-animal variation in NO<sub>3</sub> metabolism. The main objective of this thesis was to provide new knowledge about the basic biology of NO<sub>3</sub> absorption and NO<sub>2</sub> formation in ruminants, in order to increase the safety of NO<sub>3</sub> supplementation. This thesis includes a review of the literature and five experimental chapters where NO<sub>3</sub> and NO<sub>2</sub> metabolism and the effects of dietary NO<sub>3</sub> on CH<sub>4</sub> emissions, together with ruminants and the physiological effects of dietary NO<sub>3</sub> on insulin sensitivity in sheep, were evaluated. The results obtained from this thesis indicate:</p> <p>Feeding dietary NO<sub>3</sub> in combination with canola oil has a more than additive effect on reducing methanogenesis in cattle.</p> <p>Dietary NO<sub>3</sub> provided to sheep fed an otherwise highly protein-deficient diet reduces CH<sub>4</sub> emissions and provides additional N for microbial growth, including through NO<sub>3</sub>-N recycling via saliva into the gastrointestinal tract. </p> <p>Large between-animal variability in NO<sub>3</sub> metabolism in vivo and in vitro was observed throughout this thesis.</p> <p>The presence of protozoa in the rumen of sheep adapted to dietary NO<sub>3</sub> increases NO<sub>3</sub> reduction to NH3 without stimulating accumulation of NO<sub>2</sub> in the rumen; reducing the risk of NO<sub>2</sub> toxicity in ruminants.</p> <p>Faecal and urinary recovery of an intravenous dose of 15NO<sub>3</sub> was 64% after 6 days. Urinary urea-N was labelled confirming the passage of plasma NO<sub>3</sub> to the digestive tract of sheep had occurred</p> <p>This thesis found evidence of NO<sub>3</sub> accumulating in tissues of sheep for at least one hour after intravenous injection of 15NO<sub>3</sub> and 15NO<sub>2</sub>.</p> <p>Evidence of NO<sub>3</sub> and NO<sub>2</sub> being rapidly absorbed from the rumen of sheep into the blood was found. Once in the bloodstream, NO<sub>2</sub> was oxidised to NO<sub>3</sub> which is recycled via enterosalivary circulation in like manner to urea</p> <p>Nitrate and NO<sub>2</sub> are highly absorbed from the small intestine into the bloodstream, with NO<sub>2</sub> absorption responsible for high levels of blood methaemoglobin. Absorption of NO<sub>3</sub> from the abomasum to the blood was evident, whereas it is hypothesised that NO<sub>2</sub> was converted to nitric oxide in the acidic conditions of the abomasum so did not lead to high blood NO<sub>2</sub>.</p> <p>Nitrate is highly concentrated in saliva relative to blood NO<sub>3</sub> concentration</p> <p>We found no evidence that feeding a low dose of dietary NO<sub>3</sub> (18 g NO<sub>3</sub>/kg DM) affects insulin sensitivity in sheep.</p>
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Link | |
Publisher |
University of New England
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Title |
Nitrate and Nitrite Metabolism in Ruminant Livestock
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Type of document |
Thesis Doctoral
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Entity Type |
Publication
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