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 evels 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