Development and evaluation of novel technologies to reduce methane emissions focusing on forage based ruminant production systems

Enteric methane, a by-product of feed fermentation in the rumen, accounts for 44.3% of global agricultural greenhouse gas emissions. The agricultural sector is facing increasing pressure due to the need to increase food production to meet the demands of the growing population while meeting the greenhouse gas reduction targets which have been written into legally binding climate agreements. Hence, mitigation of enteric methane from ruminant livestock is now a key research focus. Dietary manipulation through the incorporation of anti-methanogenic compounds in ruminant diets has been the most widely researched and effective strategy to-date. However, the majority of the research has been reliant on offering the anti-methanogenic compound mixed into the animal’s total mixed ration. Considering that grassland and mixed systems account for 97% of global enteric methane emissions, there is a necessity to develop anti-methanogenic strategies that are applicable to predominantly forage-based systems. Seaweeds containing bromoform have consistently reduced methane production in vitro and in vivo. However, there are unresolved concerns regarding animal health and the environment with bromoform supplementation. Therefore, the first objective of this thesis was to screen a range of non-bromoform containing seaweeds in vitro for their effects on methane production and digestibility, using the rumen simulation technique system. None of the seaweeds assessed reduced methane production (Chapter 3). Subsequently, following further in vitro studies which are not presented within this thesis, a range of promising anti-methanogenic compounds were applied in vivo, in sheep (Chapter 4) and beef cattle (Chapter 5 and 6), mixed with concentrate feed and supplemented once or twice daily, respectively. Methane production was measured using portable accumulation chambers and GreenFeed technology, in sheep and beef, respectively. While brown seaweed, Ascophyllum nodosum, failed to reduce methane production in vivo (Chapter 4 and 5), isolating the anti-methanogenic agent (phlorotannins) and offering an Ascophyllum nodosum extract to sheep (Chapter 4) and beef cattle (Chapter 5), reduced methane production by 9 and 8%, respectively. Oils high in polyunsaturated fatty acids, soya oil and linseed oil, were offered to sheep (Chapter 4) and beef cattle (Chapter 5), respectively, resulting in reductions in methane production of 9 and 19%. Finally, calcium peroxide was offered to beef cattle in Chapter 6, reducing methane production by 18 and 28% at a low and a high dose, respectively. Some anti-methanogenic compounds lose their potency if subjected to processing, i.e. formulated into a pelleted feed, which is useful for delivering a homogenous feed to ruminants. Therefore, calcium peroxide was incorporated into both a coarse ration and a pellet to evaluate its processability, resulting in a 28 and 27% reduction in methane production, respectively, when offered twice daily. Surplus to the environmental effects of the compounds, the effects of the diets on animal health and performance, ruminal fermentation and diet digestibility were investigated. Essential oils and soya oil offered to sheep in Chapter 4 were the only compounds assessed that had a positive effect on animal performance. Linseed oil and calcium peroxide increased propionate production in Chapter 5 and 6, respectively. Additionally, calcium peroxide reduced total tract digestibility, which did not result in a reduction in performance. In Chapter 5, microbial DNA was extracted from rumen samples from beef cattle supplemented with linseed oil and the Ascophyllum nodosum extract. The rumen microbiome was sequenced using a metataxonomic approach to investigate the effects on microbial communities (bacteria, archaea, fungi and protozoa), resulting in subtle shifts in bacterial and fungal communities for linseed supplemented animals. The work of this thesis will contribute significantly to the continued development of anti-methanogenic dietary strategies focussing on application at pasture, with the aim of extracting the most effective anti-methanogenic agents and incorporating them in a slow-release bolus to reduce reliance on concentrate supplementation.

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University of Galway

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Attribution-NonCommercial-NoDerivatives 4.0 International

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University of Galway Theses (PhD Theses)