Future forages: Implications of forage response to climate change for ruminant production

Are our current forage-grass varieties fit for the future?

Ruminant farming enables production from marginal land that cannot be used to grow human food, thus contributing to global food security. Grazing land makes up ~60 % of the world's agricultural land supporting 360 million cattle and > 600 million sheep and goats. Continual improvement of the forage grasses used as animal feed has underpinned increases in ruminant production in an industry sector worth over £6 billion a year to the UK. Continued development of forage varieties for livestock production is essential to keep up with future demands of the growing human population.

Forage grass varieties currently under development are grown and assessed under current field conditions, Our preliminary research indicates that a change in growing conditions can affect how grass is digested and impact on animal production. Climate models predict near future (2050) increases in atmospheric CO2, increases in average temperatures, increased average precipitation, and increased frequency of extreme events. These trends are particularly pertinent to western England and Wales that are the primary sites of UK ruminant production. As it takes at least 10 years of selective breeding to go from concept to marketable product we need to know now if we are targeting the correct traits for forages of the future.

Previous work at Aberystwyth has shown that following ingestion by the animal, fresh forage feeds are degraded by enzymes of both microbial and plant origin. Grazed ryegrass entering the rumen of the animal is colonised by a subset of the microbial species present. These microbial communities are associated with the production of hydrolases, enzymes that break down plant cell walls. Efficient break down of plant cell walls in the forage is the key to energy provision for microbial growth in the rumen. If energy is limiting and plant protein breakdown is rapid, amino acids are used as an energy source generating levels of ammonia that cannot be assimilated by the animal and are excreted. This results in a loss of up to 70% of feed protein. Grazed grasses contribute to these protein losses because of stress responses to the rumen conditions. Modification of forage quality by exposure of the grass to stress during growth (eg drought) affects the process of early digestion in the rumen through stress memory; the effect of pre-exposure to a stress on the response to a subsequent stress. Hence, growth of current ryegrass varieties in a changed climate will alter the plant's response to stresses in the rumen. This will change the microbial colonisation in the rumen, which in turn will affect animal production and the environment through increased waste.

We will test the hypothesis that the response of grass leaves to climate change affects post-ingestion metabolism in plant and microbial cells, thus altering rumen system efficiency. In vitro fermentation of 10 ryegrass varieties will be assessed under current (2020) and 4 future (2050) conditions of elevated CO2 and temperature. These include scenarios that involve exposure to acute stress (drought, flooding or heat). Two varieties showing maximum and minimum differential response to at least one 2050 condition will be studied in detail to assess changes in the chemistry, protein content and composition of the forage, changes in the response of their genes to the rumen environment and how this affects the development and function of the rumen microbial communities. Predictions formed by in vitro experimentation will be confirmed with small ruminant trials to verify the whole animal effect focusing on decreasing methane and nitrogen release. The key output of our work will be to inform plant breeders on optimal targets to ensure forage grasses are fit for the future.

We will test the hypothesis that growth of forage grass under conditions typical of 2050 UK climate will invoke a stress memory response, negating predicted gains in forage grass quality from targeted breeding. Our central hypothesis is that this will be caused by a combination of plant and microbial factors in the rumen. We hypothesise that the transcriptional and post-transcriptional plant stress responses will alter microbial colonisation profiles, which will result in limited fibre degradation and decreased rumen efficiency. This is based on preliminary data demonstrating effects of forage genotype on rumen efficiency and effects pre-harvest stress on the forage transcriptome and rumen metabolome.
1) We will screen current commercial and pre-commercial ryegrass (Lolium perenne) varieties/ lines in vitro. Feed quality (dry mass, nitrogen, carbohydrates etc), fermentation efficiency (CO2, methane and volatile fatty acids), metabolic profile (including volatile organic compounds, VOCs) will be compared under 5 environmental conditions: 1) current, 2) predicted climate for 2050 (CO2 of 500 ppm and a temperature increase of 5oC) and predicted climate plus, 3) 1 week drought, 4) 1 week flood and 5) 2 d heat (40oC).
2) Two contrasting variety/ lines and 2 environment combinations (including control) will be selected for metabolomics and proteomics, transcriptomics, VOC profiles and metagenomics in a system wide network analysis of the perturbations.
3) Continuous flow fermentation will be used to test whether effects of stress memory in the forage can be overcome by adaptation by the rumen microbiota.
4) An animal trial will be used to verify predictions from the in vitro work. To minimise feed requirements small/miniature sheep will be used comparing intake, nitrogen partitioning and methane production when fed ryegrass grown under current or future scenario.
We will deliver markers for breeders to optimise forage for future climate conditions.

Ruminants provide high quality protein from land that can grow grass but cannot grow grain. Farmed grasslands in the UK represent >40 % of all land-area and provide a cost-effective platform to supply protein feed for ruminants. Maintaining productivity as the climate changes is vital to ensuring food supply and choice. Core to this is understanding the causes of inefficiency of ruminant conversion of plant into animal protein and mitigation of consequent environment damage. Improvements in rumen efficiency require improvements in the forage grasses they are fed on. We will deliver information needed to develop the next generation of grasses to optimise ruminant performance for the future climate conditions.
Understanding now how grasses perform as feeds in the near future (2050) is important because of the long timescale of breeding. This work will therefore directly benefit the UK livestock industry worth £6bn pa as well as researchers in plant, microbial and ruminant science.
1) Farmers will benefit from this research by having appropriate choice of climate ready crops to maximise pasture and animal performance under an altered climate and evidence on which to make decisions. This will indirectly contribute to social inclusion and leisure tourism by increasing the profitability and sustainability of pasture based rural life. We will engage with industry practitioners and representatives by attending industry-facing shows and co-operating with the efforts of the Farming Connect Knowledge Exchange Hub (KE Hub, a Welsh Government funded conduit for information from primary research to the farming community in Wales) and Grassland Development Centre (GDC, an extension service working with focus farms to demonstrate best practice), both based at IBERS.
2) This project will benefit forage plant breeders by providing them with information on the traits needed in future climate-appropriate forage varieties, which they can incorporate immediately into current breeding programmes. The molecular data on the response of forage grass incorporating stress memory in the rumen will inform long-term breeding strategies and provide information on biochemical pathways and target genes for breeders to use as markers in their longer-term high-throughput breeding programmes. We will ensure translation of research to product via our links with Germinal Holdings, an international grass seed company.
3) The scientific community will benefit from increased knowledge of the impact of climate change on non-model, perennial crops which are often poorly studied in comparison with annual species. We plan to produce 6 open access papers from this project spanning the continuum from frontier research into transcriptomics to verification in animals.
4) Policy makers on the reduction of greenhouse gas emissions will benefit from the outputs of this project through improved understanding of effects of climate change on forage digestion and hence on the knock on effects for meeting emission targets set for livestock.
5) There will be a strong training aspect in this project. The PDRAs will benefit from experience of a multifaceted project. They will be expected to present the work at conferences and contribute to writing of publications, so developing their career skills.
6) Consumers will benefit from increased sustainability of ruminant farming delivering cost-effective animal protein. The public will also gain from the environmental benefits in addressing ruminant efficiency thus reducing waste production, which contributes to greenhouse gas emissions and run off from fields. Finally, the gains made in animal productivity by correct tailoring of the forage grass varieties in 2050 will potentially reducing land dedicated to grazing that could be used for growing food crops, and hence both directly and indirectly support food security.