The use of lactic acid bacteria as methane mitigation strategies in ruminants

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Doyle, Natasha
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University College Cork
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Lactic acid bacteria (LAB) have often been cited as potential strategies for the reduction of methane emissions from ruminants, however more research is needed to identify whether LAB can be an effective methane mitigation option in ruminant livestock. The aim of this thesis was to investigate the potential of LAB as methane mitigation strategies in ruminants, by determining the effect of LAB on methane production, animal health and productivity. Chapter 1, a literature review, addresses the topic of greenhouse gas (GHG) emissions in agriculture, including methane, nitrous oxide and carbon dioxide. Methane production from ruminants is influenced by a wide variety of factors, including feed additives such as lactic acid-utilizing bacteria, LAB and yeast. This chapter focuses on the use of direct fed microbials (DFMs) for the reduction of GHG emissions in agriculture. The strengths and challenges associated with each strategy are also explored. Chapter 2 focuses on the use of LAB specifically for methane mitigation in ruminants. Enteric fermentation is the largest anthropogenic source of agricultural methane and, as such, requires innovative solutions for the reduction of methane from livestock. This chapter reviews current literature and provides a comprehensive analysis on the potential use of LAB as methane mitigation strategies. To determine the methane mitigation potential of LAB, several species of methanogens (methane producing microorganisms) were cultivated. In Chapter 3, a total of 6 methanogenic species of both human and ruminant origin were cultivated. Methanobrevibacter ruminantium and Methanobrevibacter gottschalkii were chosen for cultivation as they comprise ~75% of the archaeal population within the rumen. Several human methanogens were also chosen for cultivation to allow for comparison of cultivation techniques required for these methane producing microorganisms and for the determination of methane production from several methanogenic strains. Gas chromatography methods determined that methanogens of rumen origin produced almost 4000 times more methane (90g/L) in vitro, when compared to human methanogen strains (0.025g/L). Establishment of methanogen cultivation techniques were essential to allow for further research to be carried out in Chapter 4. Methane inhibition trials assessed the potential of LAB and various bacterial families, including Staphylococcus, for the reduction of methane in vitro. Staphylococcus capitis APC 2918 resulted in the best methane inhibition of 54% and 69% in Methanobrevibacter ruminantium and Methanobrevibacter gottschalkii, respectively. Commercially available LAB strains (provided by a commercial partner), Lactobacillus plantarum LP58 and Lactococcus lactis subsp. lactis SL242, demonstrated methane reduction up to 28% against Mbb. gottschalkii (P <0.05). The screening process reported in chapter 4 resulted in a biobank of 20 strains with bacteriocin capabilities and possible anti-methanogenic potential. Both of the commercially available LAB strains, Lactobacillus plantarum LP58 and Lactococcus lactis subsp. lactis SL242, with demonstrated methane reduction effects of 9-28% in vitro, were chosen as silage co-inoculants for use in an animal intervention study. Chapter 5 determined the effects of these LAB co-inoculants on silage quality. LAB when administered as co-inoculants resulted in good quality silage in terms of pH (4.27, SD 0.653), dry matter percentages (26%, SD 1.532) and overall appearance. However, when compared to control silage with no silage inoculant, little statistical difference was seen. This LAB inoculated silage was subsequently used in a 7 week animal intervention study in Chapter 6. Animal intervention studies resulted in reduced methane emissions of 5.7% (P < 0.01) in 30 late-lactating Holstein dairy cattle. Ruminal content of cattle fed LAB inoculants resulted in a 2-log reduction of Proteobacteria (P = 0.006), a major phylum of gram-negative bacteria. Cyanobacteria were also significantly reduced by ~3 logs in treatment cattle (P = 0.007). Cattle treated with LAB inoculated silage produced milk with high lactose content (4.6%, P<0.05), reduced milk urea nitrogen between weeks 2 and 5 of the animal intervention (P< 0.05), and greater free fatty acids (9.92%, P <0.05). Taken together, the results of this thesis demonstrate that LAB provide an effective solution for the reduction of methane emissions in ruminants, while simultaneously improving animal health and maintaining productivity. Through the knowledge gathered, it can be said that LAB have the potential to provide methane mitigation solutions which will aid in the development of a competitive and sustainable Agri-food sector.
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Lactic acid bacteria , Ruminants , Methane , Mitigation , Bacteriocins
Doyle, N. J. 2023. The use of lactic acid bacteria as methane mitigation strategies in ruminants. PhD Thesis, University College Cork.