Feed for Net Zero: Understanding the structure function relationships in forages driving rumen feed degradation

Background & JustificationRuminants are a vital part of the food supply chain, delivering nutritious products from land that produces food inedible by humans. Forage grasses are the main source of nutrition for ruminant livestock in the UK. While the evolution of the rumen microbial community enables fermentation of fibrous feed, a by-product is emission of methane and ammonia. Methane release is linked to efficiency of rumen digestion of the "fibre" part in the feed. We hypothesise that there is an optimal composition making up the "fibre" part of the forage feed which drives a colonisation profile that maximises fermentation but minimises methanogenesis. Furthermore, we predict that environmental stress will perturb cell wall biochemistry to alter colonisation and hence feed use efficiency.Livestock-based methane emissions decrease with increased digestibility and nutritional value of forage grasses. This is described as Neutral Digestible Fibre (NDF) and Acid Digestible Fibre (ADF). These terms broadly measure cellulose, hemicellulose, lignin and pectin in the cell walls but do not describe how the fundamental compositional differences between grasses affects colonisation. We have demonstrated successional colonisation of ingested forage, with defined microbial communities forming in phases over 24h. The timing can be affected by substrate but more information is needed about the effect of substrate on community composition and the functional roles of the microbiota at the various stages. Also, future climate scenarios predict increasingly erratic and extreme weather patterns in the UK. Cell walls, representing ~70% of a plant dry weight, adapt their composition and structure in response to external challenges to maintain cell integrity. Cell wall components have been associated with drought tolerance and drought stress decreases the digestibility of forage grasses. Likewise, exposure to wind resulted in increased lignin content and reduced digestibility. A metagenomics approach linked to plant biochemistry will be used to explore these relationships.Aim and ObjectivesWe hypothesise that environmental stress will alter forage cell wall composition and structure (and thus quality/nutritive value) which leads to changes in GHG emissions. Understanding the interaction between environmental stresses, cell wall characteristics and GHGs is essential to help deliver Net Zero grassland-based food systems1. We will establish the effect of environmental stresses on cell wall quality of forage grasses. In consultation with the grass breeding company Germinal, three leading forage grass varieties will be grown under controlled environment and exposed to a range of environmental stresses (drought, heat, wind, flooding) to detect treatment induced changes in cell wall composition (lignin, cellulose, hemicellulose). Environmental stresses also affect the cell wall pectins. ELISA assays with antibodies that represent markers for different forms of pectins will provide information on stress induced changes to pectin.2. We will determine if stress induced changes in cell wall properties impact the in vitro digestibility of forage grasses. Biomass samples of each of the forage grasses exposed to the different environmental stresses will be exposed to a rumen fluid inoculum and total gas production, CO2 and methane measured. Samples of the rumen inoculum will be used for FTIR analysis to explore differences in metabolite production.3. Establish microbiome and colonisation profiles. Samples from in vitro incubation of grasses and rumen microbiota will be subject to metagenomics and metatranscriptomic analysis to establish the taxonomy profile during colonisation of the plant material and the related transcriptomic profiles within and between microbial communities in response to changes in the plant carbohydrate structure.