Wu L, Harris P, Misselbrook T H, Lee M R F
Sustainable Agriculture Sciences, Rothamsted Research, North Wyke, Devon EX20 2SB, UK.
Bristol Veterinary School, University of Bristol, Langford, Somerset BS40 5DU, UK.
Agric Syst. 2022 Jan;195:103307. doi: 10.1016/j.agsy.2021.103307.
Ruminant livestock make an important contribution to global food security by converting feed that is unsuitable for human consumption into high value food protein, demand for which is currently increasing at an unprecedented rate because of increasing global population and income levels. Factors affecting production efficiency, product quality, and consumer acceptability, such as animal fertility, health and welfare, will ultimately define the sustainability of ruminant production systems. These more complex systems can be developed and analysed by using models that can predict system responses to environment and management.
We present a framework that dynamically models, using a process-based and mechanistic approach, animal and grass growth, nutrient cycling and water redistribution in a soil profile taking into account the effects of animal genotype, climate, feed quality and quantity on livestock production, greenhouse gas emissions, water use and quality, and nutrient cycling in a grazing system.
A component to estimate ruminant animal growth was developed and integrated with the existing components of the SPACSYS model. Intake of herbage and/or concentrates and partitioning of the energy and protein contained in consumed herbage and/or concentrates were simulated in the component. Simulated animal growth was validated using liveweight data from over 200 finishing beef cattle and 900 lambs collected from the North Wyke Farm Platform (NWFP) in southwest England, UK, between 2011 and 2018. Annual nitrous oxide (NO), ammonia, methane and carbon dioxide emissions from individual fields were simulated based on previous validated parameters.
A series of statistical indicators demonstrated that the model could simulate liveweight gain of beef cattle and lamb. Simulated nitrogen (N) cycling estimated N input of 190 to 260 kg ha, of which 37-61% was removed from the fields either as silage or animal intake, 15-26% was lost through surface runoff or lateral drainage and 1.14% was emitted to the atmosphere as NO. About 13% of the manure N applied to the NWFP and excreta N deposited at grazing was lost via ammonia volatilisation.
The extended model has the potential to investigate the responses of the system on and consequences of a range of agronomic management and grazing strategies. However, modelling of multi-species swards needs to be validated including the dynamics of individual species in the swards, preferential selection by grazing animals and the impact on animal growth and nutrient flows.
反刍家畜通过将不适于人类食用的饲料转化为高价值的食物蛋白，对全球粮食安全做出了重要贡献。由于全球人口和收入水平的不断提高，目前对这种食物蛋白的需求正以前所未有的速度增长。影响生产效率、产品质量和消费者接受度的因素，如动物繁殖力、健康和福利，将最终决定反刍生产系统的可持续性。可以通过使用能够预测系统对环境和管理措施反应的模型来开发和分析这些更为复杂的系统。
我们提出了一个框架，该框架采用基于过程的机理方法，动态模拟动物和牧草生长、土壤剖面中的养分循环和水分再分配，同时考虑动物基因型、气候、饲料质量和数量对畜牧生产、温室气体排放、用水和水质以及放牧系统中养分循环的影响。
开发了一个估算反刍动物生长的组件，并将其与SPACSYS模型的现有组件集成。在该组件中模拟了牧草和/或精饲料的摄入量以及所消耗的牧草和/或精饲料中所含能量和蛋白质的分配情况。利用2011年至2018年期间从英国英格兰西南部的北威克农场平台（NWFP）收集的200多头育肥牛和900只羔羊的体重数据，对模拟的动物生长情况进行了验证。根据先前验证的参数，模拟了各个田地每年的一氧化二氮（N₂O）、氨、甲烷和二氧化碳排放量。
一系列统计指标表明该模型能够模拟肉牛和羔羊的体重增加。模拟的氮（N）循环估算出氮输入量为190至260千克/公顷，其中37%至61%以青贮饲料或动物摄入量的形式从田地中去除，15%至26%通过地表径流或侧向排水流失，1.14%以N₂O的形式排放到大气中。施用于NWFP的粪肥氮和约三分之一的放牧时沉积的排泄物氮通过氨挥发而损失。
扩展后的模型有潜力研究该系统对一系列农艺管理和放牧策略的反应及其后果。然而，多物种草地的建模需要进行验证，包括草地中各个物种的动态、放牧动物的优先选择以及对动物生长和养分流动的影响。
