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

我们现在的牧草品种适合未来吗？反刍动物养殖使不能用来种植人类粮食的边际土地得以生产，从而为全球粮食安全作出贡献。牧场占世界农业用地的60%，可饲养3.6亿头牛和6亿只绵羊和山羊。作为动物饲料的饲草的持续改进支撑了英国每年价值超过60亿GB的工业部门反刍动物产量的增加。继续开发用于畜牧业生产的牧草品种，对于满足不断增长的人口的未来需求至关重要。目前正在开发的牧草品种是在目前的田间条件下种植和评估的，我们的初步研究表明，生长条件的变化可能会影响草的消化方式，并对动物生产产生影响。气候模型预测，在不久的将来(2050年)，大气中的二氧化碳会增加，平均气温会升高，平均降水量会增加，极端事件的发生频率也会增加。这些趋势与英格兰西部和威尔士特别相关，这些地区是英国反刍动物的主要生产地。由于至少需要10年的选择性育种才能从概念转化为可销售的产品，我们现在需要知道我们是否针对未来的牧草选择了正确的性状。Aberystwyth之前的研究表明，动物摄入新鲜饲料后，微生物和植物来源的酶都会降解新鲜饲料。被放牧的黑麦草进入动物的瘤胃，由存在的微生物物种的子集定植。这些微生物群落与水解酶的产生有关，水解酶是一种分解植物细胞壁的酶。饲料中植物细胞壁的有效分解是为瘤胃微生物生长提供能量的关键。如果能量有限，植物蛋白质分解迅速，氨基酸就被用作能量来源，产生动物无法同化并被排泄的氨。这会导致饲料蛋白质损失高达70%。由于对瘤胃条件的压力反应，牧草造成了这些蛋白质的损失。牧草在生长期间暴露于胁迫(如干旱)而改变饲草品质，通过胁迫记忆影响瘤胃早期消化过程；预先暴露于胁迫对后续胁迫的反应的影响。因此，当前黑麦草品种在气候变化中的生长将改变植物对瘤胃压力的反应。这将改变瘤胃中的微生物定植，进而通过增加排泄物影响动物生产和环境。我们将检验这一假设，即草叶对气候变化的反应会影响植物和微生物细胞的摄食后新陈代谢，从而改变瘤胃系统的效率。10个黑麦草品种的体外发酵将在当前(2020)和4个未来(2050)二氧化碳和温度升高的条件下进行评估。这些情况包括暴露在严重压力(干旱、洪水或高温)下的情景。将对两个品种进行详细研究，以评估饲料的化学成分、蛋白质含量和组成的变化，它们的基因对瘤胃环境的反应的变化，以及这如何影响瘤胃微生物群落的发展和功能。通过体外实验形成的预测将得到小型反刍动物试验的证实，以验证整个动物的效果，重点是减少甲烷和氮的释放。我们工作的关键成果将是告知植物育种者最优目标，以确保牧草适合未来。

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.